WO2019170781A1

WO2019170781A1 - A resonant power converter

Info

Publication number: WO2019170781A1
Application number: PCT/EP2019/055621
Authority: WO
Inventors: Riccardo PITTINI; Martin Schøler RØDGAARD; Thomas Andersen; Toke Meyer ANDERSEN; Jakob Døllner MØNSTER; Mickey P MADSEN
Original assignee: Npc Tech Aps
Current assignee: Npc Tech Aps
Priority date: 2018-03-06
Filing date: 2019-03-06
Publication date: 2019-09-12
Anticipated expiration: 2020-09-06

Abstract

The present invention relates to a resonant power converter (100) comprising an input side circuit comprising a positive and a negative input terminal for receipt of an input voltage; a controllable switch arrangement (200) configured to be driven by a switch control signal (355) to control a switching frequency of the resonant power converter (100); a resonant network or tank (300) coupled to an output of the controllable switch arrangement (200) to generate alternatingly increasing and decreasing resonant current in the resonant network or tank (300) in accordance with the switch control signal (355), the resonant network or tank (300) comprising at least one inductor (302) and at least one capacitor (301), wherein the resonant network or tank (300) comprises an adjustable reactance to change an impedance of the resonant network or tank (300), and wherein the adjustable reactance comprises at least one of an inductor with adjustable inductance and a capacitor with adjustable capacitance.

Description

A RESONANT POWER CONVERTER

The present invention relates to a resonant power converter comprising an input side circuit comprising a positive and a negative input terminal for receipt of an input voltage. A controllable switch arrangement, driven by a switch control signal, is con- figured for controlling a switching frequency of the resonant power converter. A res- onant network or resonant tank is coupled to an output of the controllable switch arrangement to generate alternatingly increasing and decreasing resonant current in the resonant network or tank in accordance with the switch control signal, where the resonant network or tank comprises at least one inductor and at least one capacitor.

BACKGROUND OF THE INVENTION

Power density and component costs are key performance metrics of both isolated and non-isolated power converters to provide the smallest possible physical size and/or lowest costs for a given output power requirement or specification. Resonant power converters are particularly useful for high switching frequencies such as fre- quencies above 1 MHz where switching losses of standard SMPS topologies (Buck, Boost etc.) tend to be unacceptable for conversion efficiency reasons. High switch- ing frequencies are generally desirable because of the resulting decrease of the electrical and physical size of circuit components of the power converter like induc- tors and capacitors. The smaller components allow increase of the power density of the power converter. In a resonant power converter, an input "chopper" semiconduc- tor switch (often MOSFET or IGBT) of the standard SMPS is replaced by a "reso- nant" semiconductor switch. The resonant semiconductor switch relies on reso- nances of a resonant network typically involving various circuit capacitances and inductances to shape the waveform of either the current or the voltage across the semiconductor switch such that, when state switching takes place, there is no cur- rent through or no voltage across the semiconductor switch. Hence power dissipa- tion is largely eliminated in at least some of the intrinsic capacitances or inductances of the input semiconductor switch such that a dramatic increase of the switching frequency into the VHF range becomes feasible for example to values above 30 MHz. This concept is known in the art under designations like zero voltage and/or zero current switching (ZVS and/or ZCS) operation. Commonly used switched mode power converters operating under ZVS and/or ZCS are often described as class E, class F, or class DE inverters or power converters.

It is desirable for many types of resonant power converters to be capable of operat- ing with variable and/wide voltage input and/or output ranges as this provides flexi bility during operation, e.g. for universal mains power adapter, and furthermore since this also allows for minimizing the size of respective passive components.

Certain known designs of resonant power converters rely on varying an operating frequency to control the power transfer and thereby facilitate variable and/wide volt- age input and/or output ranges. However, at least in some cases this is not sufficient or optimal, or even possible, e.g. for self-oscillating systems.

Additionally, certain other designs of resonant power converters rely on varying the voltage transfer ratio of a transformer to achieve impedance matching and thereby facilitate variable and/wide voltage input and/or output ranges. However, in some cases this is not sufficient or optimal, or even possible, as it would require varying the resonant elements for efficient operation.

Patent application US 2014/225439 discloses a power converter having a switch network coupled to an input voltage, a power transformer having a primary winding and a secondary winding, wherein the primary winding is coupled to the switch net- work, and the secondary winding is coupled to a rectifier. The rectifier is coupled to an output voltage and a primary resonant tank having a first resonant capacitor. A regulation circuit is configured to control the output voltage of the power converter to be substantially proportional to the input voltage and the switch network to operate at a frequency substantially close to a first resonant frequency. Patent application WO2017068521 A1 discloses a resonant power converter where capacitors of the resonant tank are connected in/out via switches. However, in some cases this is not sufficient and it is necessary to vary the both inductive and capacitive elements in the resonant tank, e.g. when wide converter operation is required for self-oscillating systems. This becomes even more challenging when the transformer integrates one or more resonant elements. Patent application WO2017068521 A1 discloses an electronic -bridge converter comprising a half-bridge, a transformer, and a first ca- pacitor on a primary side, and a diode, a second capacitor, and an inductor on a secondary. However no disclosure is given of how to vary transformer magnetizing and/or leakage inductance to allow a wide-voltage and/or power efficient operation of a resonant power converter. Patent application W02016167501 A1 discloses a resonant power converter with a resonant circuit on a secondary side where a trans- former with a tap switching arrangement is shown and used for voltage matching. However, WO2016167501 A1 does not teach how to match resonant elements as required for self-oscillating systems where the transformer is one of the main ele- ments of the resonant tank. Patent application US 20170346410 A1 discloses a power converter where transformer taps are selected based on a desired output voltage and/or based on a level of the mains voltage. However, according to patent application US 20170346410 A1 , the output power is controlled by duty cycle of the generator and the resonant tank is formed with a transformer magnetizing induct- ance from the tapped winding. In some cases, adjusting the duty cycle of the switches is not possible and/or varying of the switching frequency is not possible, e.g. for self-oscillating systems. In at least some resonant converters, voltage matching via a transformer is not as significant as matching resonant elements in order to achieve efficient system operation.

Therefore, it is, at least for certain types of resonant power converters, still a signifi cant challenge to realize reliable operation with variable and/wide voltage input and/or output ranges, especially if also aiming at having or maintaining high system efficiency.

In view of these problems and challenges associated with prior art operation of res- onant power converters, it would be advantageous to provide a resonant power converter being able to deliver a controlled power output, especially for resonant power converters that should or needs to operate with variable and/or wide input and/or output ranges.

SUMMARY OF THE INVENTION

A first aspect of the invention relates to a resonant power converter comprising:

- an input side circuit comprising a positive and a negative input terminal for receipt of an input voltage, - a controllable switch arrangement configured to driven by a switch control signal to control a switching frequency of the resonant power converter,

- a resonant network or tank coupled to an output of the controllable switch ar- rangement to generate alternatingly increasing and decreasing resonant cur- rent in the resonant network or tank in accordance with the switch control signal, the resonant network or tank comprising at least one inductor and at least one capacitor,

wherein the resonant network or tank comprises an adjustable reactance to change an impedance of the resonant network or tank, and where the adjustable reactance comprises at least one of an inductor with adjustable inductance and a capacitor with adjustable capacitance.

The adjustable reactance of the resonant network or tank enables a selectively ad- justment of inductance and/or capacitance of the resonant network or tank thereby enabling selectively adjusting the reactance of the resonant network or tank. The inductance and/or a capacitance of the resonant network or tank may e.g. be selec- tively adjusted in response to a control signal. Adjusting the reactance adjusts the impedance of the resonant network or tank. In this way, impedance control is pro- vided for a resonant power converter, and in particular a controlled power output is provided even when operating with variable and/or wide voltage input and/or output ranges.

The resonant power converter as disclosed herein may in some embodiments be a resonant DC-DC power converter (then e.g. comprising or be connected to a rectifi er element or circuit or similar) or alternatively be a resonant AC-DC power convert- er.

The controllable switch arrangement may, at least in some embodiments, comprise a feedback network and/or be self-oscillating and e.g. comprise a self-oscillating driver or self-oscillating gate driver.

The frequency of the switch control signal, controlling the switching frequency of the resonant power converter, may be set to a frequency at or above 1 MHz, preferably at or above 5 MHz, even more preferably at or above 10 MHz, even more preferably at or above 15 MHz. The frequency of the switch control signal may even more preferably be set to a frequency at or above 20 MHz, for example in the so-called VHF range at or above 30 MHz. A resonance frequency of the resonant network or tank is preferably situated in proximity of the selected switching frequency of the resonant power converter. The resonant power converter is preferably configured to provide zero voltage and/or zero current switching of the semiconductor switch of the controllable switch arrangement.

The switch control signal may e.g. be set in response to one or more external sig nals, be set by a resonant network (e.g. a self-oscillating gate driver), etc.

In some further embodiments, the inductor comprises a fixed inductor segment and a switchable inductor segment connected in series, and a controllable switch config- ured to selectively connecting and disconnecting the switchable inductor segment from the resonant network to adjust the reactance of thereof. By a switchable induc- tor (and variations thereof) and by a switchable capacitor (and variations thereof) as disclosed herein is to be understood that the respective component may controllably be switched in and out of the resonant network or tank (or any other relevant circuit). When switching out a switchable inductor it is bypassed while a connection of a switchable capacitor is broken or set to off when being switched out.

In some further embodiments, the switchable inductor segment comprises a first end connected to the fixed inductor segment and a second end connected to an electri- cal reference potential such as electrical ground, and wherein the controllable switch is connected between the electrical reference potential and the first end of the switchable inductor segment. Herein, a fixed inductor segment may also be referred to as an inductor and a switchable inductor segment may also be referred to as a switchable inductor.

In some further embodiments, the fixed inductor segment comprises a first set of inductor windings and the switchable inductor segment comprises a second of in- ductor windings; said first and second sets of inductor windings being arranged on a common magnetic core. In some embodiments, the resonant power converter further comprises an isolation transformer coupling a primary side circuit and a secondary side circuit of the power converter.

In some embodiments, the least one inductor of the resonant network or tank is ar- ranged in the secondary side circuit and the at least one capacitor is arranged in the primary side circuit.

In some further embodiments, the resonant power converter is configured to adjust the reactance of the resonant network or tank by adjusting a turns ratio of the isola- tion transformer.

In some embodiments, the resonant power converter further comprises an isolation transformer coupling a primary side circuit and a secondary side circuit of the power converter and wherein the isolation transformer is configured to provide a leakage inductance as at least a part of the inductor with adjustable inductance. In this way, a leakage inductance of the transformer is used as part of the resonant network or tank e.g. instead of the (indirectly) adjustable inductor.

In some further embodiments,

- the resonant power converter further comprises a(isolation) transformer comprising a primary side and a secondary side,

- the primary side is coupled between at least one capacitor of the resonant network or tank and a load, and

- wherein the secondary side is coupled between at least one switchable reac- tance element configured to adjust an inductance of the primary side.

In some further embodiments, the resonant power converter further comprises a plurality of switchable tuning capacitive elements arranged in parallel and each re- spectively being connected at a first end to the secondary side of the (isolation) transformer and at a second end to an electrical reference potential such as electri cal ground via a controllable switch. This e.g. enables soft switching and/or control of a power flow between the controllable switch arrangement and the load. By add- ing one or more windings to the resonant tank (auxiliary windings) it is possible to vary its equivalent impedance by connecting and disconnecting the switchable tun- ing capacitive elements via appropriate switches.

In some alternative further embodiments, the resonant power converter further corn- prises a fixed tuning inductive element and a switchable tuning inductive element connected in series, and a controllable switch configured to selectively connecting and disconnecting the switchable tuning inductive element from the resonant net- work or tank to adjust the reactance of thereof. In some further embodiments, the switchable tuning inductive element comprises a first end connected to the fixed tuning inductive element and a second end connected to an electrical reference po- tential such as electrical ground, and wherein the controllable switch is connected between the electrical reference potential and the first end of the switchable tuning inductive element.

In some embodiments,

- the resonant power converter further comprises a transformer or an isolation transformer comprising a primary side and a secondary side,

- the secondary side is at least a part of the inductor with adjustable induct- ance,

wherein

- the resonant power converter further comprises a plurality of switchable tun- ing capacitive elements arranged in parallel and each respectively being connected at a first end to the secondary side of the (isolation) transformer and at a second end to an electrical reference potential such as electrical ground via a controllable switch,

or

- the resonant power converter further comprises a fixed tuning inductive ele- ment and a switchable tuning inductive element connected in series, and a controllable switch configured to selectively connecting and disconnecting the switchable tuning inductive element from the resonant network or tank to adjust the reactance of thereof. In some embodiments, the resonant power converter comprises one or more further switchable capacitors located between the resonant network or tank and a load.

In some embodiments, the capacitor comprises a fixed capacitor segment and a switchable capacitor segment connected in parallel, and a controllable switch con- figured to selectively connecting and disconnecting the switchable capacitor seg- ment from the resonant network to adjust the reactance of thereof.

In some embodiments, the resonant power converter is a resonant DCDC converter configured to adjust the impedance of the resonant network or tank by adjusting the turns ratio of a primary side of the isolation transformer.

In some embodiments, the resonant power converter is a resonant ACDC converter configured to adjust the impedance of the resonant network or tank by adjusting the turns ratio of a primary side of the isolation transformer.

In some embodiments, the resonant power converter is a resonant DCDC converter configured to adjust the impedance of the resonant network or tank by adjusting the turns ratio of a secondary side of the isolation transformer.

In some embodiments (and/or according to a second aspect), the resonant network or tank comprises an isolation transformer coupling a primary side circuit and a sec- ondary side circuit of the power converter, where the isolation transformer compris- es a first set of inductor windings and a second set of inductor windings arranged on a common magnetic core. The isolation transformer further comprises a first leakage inductance and at least a second leakage inductance. A first end of the first leakage inductance is connected in series with a first end of the first set of inductor windings and a second end of the first set of inductor windings is connected in series with a first end of the second leakage inductance at an intermediate point. Furthermore, a second end of the second leakage inductance is connected in series with a first end of the second set of inductor windings. In some embodiments, the sets of windings and the leakage inductances are part of the primary side circuit then with the sec- ondary side circuit comprising secondary side windings. In some alternative embod- iments, the sets of windings and the leakage inductances are part of the secondary side circuit then with the primary side circuit comprising primary side windings.

Additionally, the resonant power converter or the resonant network or tank is config- ured to selectively connect and disconnect the second leakage inductance and the second set of inductor windings to and from, respectively, the resonant network or tank to adjust the reactance of thereof.

In this way, leakage inductance(s) of the transformer is used as a part of the reso- nant network or tank (used as a resonant element) to readily enabling variation or adjustment of the reactance thereby changing the impedance of the resonant net- work or tank in a controllable way. Compared with some of the above embodiments, this e.g. avoids using a specific adjustable inductor component or circuit reducing implementation size and power consumption while still maintaining controlled power output even when operating with variable and/or wide voltage input and/or output ranges. Additionally, operational range of both power and voltage levels are provid- ed, since the impedance of the resonant network or tank can be adjusted to match the specific operating point at changing input and/or output voltages.

More specifically, the transformer turns ratio (and thereby the effective leakage in- ductance and ultimately the resulting impedance of the resonant network or tank) may be controlled and varied depending on an operating mode of the system, e.g. low or high input voltage range and/or e.g. in dependence of a desired power level (high or low). The controllability of the resonant power converter is improved as it is possible to control and regulate the output power and to achieve lower system loss- es by matching the resonant elements with a desired output power, and/or input voltage, and/or output voltage extending its operational range.

It is noted, that controllably varying or adjusting an integrated leakage inductance of the transformer in such ways is different e.g. to implementations where a transform- er is used for voltage matching between a primary and a secondary side, where a transformer is not a resonant element of a resonant network or tank, etc. The resonant power converter may readily support more than two operating modes by using additional taps (and thereby additional parts of the windings), additional resonant inductances, and additional switches (one of each for each additional mode).

In some embodiments, the intermediate point and a second end of the second set of inductor windings are each connected via a respective controllable switch to an electrical reference potential such as electrical ground. In particular, such switches provide control depending on a desired power level (most significant) and potentially also voltage level input.

In some embodiments, the at least one capacitor is arranged in the primary side circuit of the isolation transformer where the at least one capacitor is connected to a second end of the first leakage inductance or alternatively is connected to a primary winding of the isolation transformer.

In some embodiments, the at least one capacitor comprises two capacitors where one of the two capacitors is connected to the intermediate point and the other of the two capacitors is connected to a second end of the second set of inductor windings.

In some embodiments, the first set of inductor windings; the second set of inductor windings; the intermediate point; the first leakage inductance; and the at least a second leakage inductance are located in the primary side circuit of the isolation transformer. Alternatively they are located in the secondary side circuit of the isola- tion transformer.

In at least some embodiments of a resonant power converter as disclosed herein comprising a transformer and adjusting a turns ratio of the transformer, the turns is adjusted using one or more transformer taps of either the primary or the secondary transformer winding. In such embodiments, the transformer may comprise one or more taps at respective intermediate points on the respective winding (on either side depending on specific embodiment), for adjustment. Taps may e.g. be manually reconnected, or a manual or automatic switch may be provided for changing be- tween taps. The transformer tap(s) may e.g. also be implemented as discrete sepa- rate windings. In effect, the taps (or other corresponding measures) allow for varying the effective transformer turns ratio thus providing scaling of an output load imped- ance and scaling of the inductance of the tank inductor. A mentioned isolation trans- form can, at least in some embodiments, simply be a transformer.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described in more detail in connec- tion with the appended drawings, in which:

FIG. 1 shows a simplified schematic electrical circuit diagram of an exemplary reso- nant power converter;

FIG. 2A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with one embodiment of the invention;

FIG. 2B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 2A;

FIG. 2C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 2B;

FIG. 2D shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet an alternative embodiment of the resonant power converter of FIG. 2A;

FIG. 2E shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet an alternative embodiment of the resonant power converter of FIG. 2B,

FIG. 3A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with another embodiment of the invention;

FIG. 3B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3A;

FIG. 3C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3A; FIG. 3D shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3B;

FIG. 3E shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3B;

FIG. 4A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet another embodiment of the invention;

FIG. 4B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention;

FIG. 5A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 4A);

FIG. 5B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a more detailed implementation of the resonant power converter of FIG. 5A;

FIG. 5C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention;

FIG. 5D shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention;

FIG. 5E shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention;

FIG. 6A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet another embodiment of the invention;

FIG. 6B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 6A;

FIG. 7 shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 6A;

FIG. 8A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention; FIG. 8B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 8A; and

FIG. 8C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 8B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a simplified schematic electrical circuit diagram of an exemplary reso- nant power converter.

Illustrated is a resonant high-frequency class DE power converter 100 comprising a controllable switch arrangement 200, a resonant network (also sometimes referred to as tank, resonance tank, or similar) 300, and a converter load 1 15 (forth also equally referred to simply as load). The controllable switch arrangement 200 is driv- en by a switch control signal (355) to control a switching frequency of the resonant power converter 100. An input of the resonant network or tank 300 is coupled to an output of the controllable switch arrangement to generate alternatingly increasing and decreasing resonant current in the resonant network or tank 300 in accordance with the switch control signal and the output of the resonant network or tank 300 is coupled to an input of the load 1 15. The controllable switch arrangement 200 and the load 1 15 are both connected to electrical ground or an electrical reference po- tential (forth both equally referred to as ground). The resonant network or tank 300 comprises a tank inductor 302 (labelled L_Tank) and a tank capacitor 301 (labelled C_Tank) connected in series. The load 1 15 of the power converter 100 may for ex- ample be a set of LED diodes, a rechargeable battery, or other suitable systems and/or components. The controllable switch arrangement 200 may, at least in some embodiments, comprise a feedback network and/or be self-oscillating and e.g. corn- prise a self-oscillating driver or self-oscillating gate driver. The resonant power con- verter may be a resonant DC-DC power converter (then e.g. comprising or be con- nected to a rectifier element or circuit or similar) or alternatively be a resonant AC- DC power converter (as is shown in Fig. 1 ). The tank capacitor 301 primarily acts - in the shown power converter 100 - as a DC current blocker, as the controllable switch arrangement 200 typically will have a DC component (e.g. half of the supply voltage for a class DE power converter) and will limit the resonance current to only an AC current. The tank inductor 302 limits the level of current being received by the load 1 15 when an AC voltage signal is applied to the controllable switch arrangement 200. The inductance of the tank inductor 302 and the resistance of the load 115 are typically selected to achieve a specific output power, which amongst others generally is highly dependent on the input voltage as well as switching devices and switching frequency of the controllable switch ar- rangement 200.

However, as the resonance current roughly is proportional to the input voltage, the output power becomes proportional to the square of the input voltage for the reso- nant power converter. This entails that a doubling of input voltage, such as 200 V to 400 V) results in four times the output power. This in turn makes it very difficult to implement an optimal and efficient design without having to over-dimension basical- ly all involved components, which would otherwise lead to increased cost and size of the components as well as sacrificing performance and efficiency.

FIG. 2A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with one embodiment of the invention.

Shown is a resonant power converter 100 according to an embodiment of the inven- tion that comprises a controllable switch arrangement 200, a resonant network or tank 300, and a converter load 1 15.

The controllable switch arrangement 200 and/or the converter load 1 15 may, at least in some embodiments, correspond to the controllable switch arrangement 200 and/or the load of FIG. 1. The resonant network or tank 300 comprises an inductor 302 (labelled L_Tank in FIG. 2A) and a capacitor 301 (labelled C_Tank in FIG. 2A). However, in accordance with aspects of the present invention, (at least) the reso- nant network or tank 300 differs from the one in FIG. 1 as will be explained further in the following. Generally, the resonant network or tank 300 comprises at least one inductor 302 and/or at least one capacitor 301. The load 1 15 schematically illustrat- ed in FIG. 2A is a resistive load. However, it is to be understood that the load 115, in this and all other embodiments as disclosed herein, may by other types of loads, such as a rectifier to a DC voltage, a half-bridge rectifier, a full-bridge rectifier, etc.

According to aspects of the present invention, the resonant network or tank 300 has an adjustable reactance and is configured to selectively adjust an inductance and/or a capacitance (in the shown embodiment adjusting only the capacitance) of the res- onant network or tank 300 thereby adjusting the reactance of the resonant network or tank 300. The capacitance of the resonant network or tank 300 is selectively ad- justed, at least in some embodiments, in response to a control signal. Adjusting the reactance adjusts the impedance of the resonant network or tank 300. In this way, impedance control is provided for a resonant power converter, and in particular a controlled power output is provided even when operating with variable and/or wide voltage input and/or output ranges.

In some embodiments, and as shown in FIG. 2A, at least one of the capacitors 301 of the power converter 100 is a switchable capacitor 30T (labelled C_Tank3 in FIG. 2A) preferably, but not necessarily, connected to electrical ground. This is advanta- geous, since it is much simpler to control a ground related switch compared to a non-ground related switch in this context. According to some embodiments, the res- onant network or tank 300 is configured to selectively adjust its reactance in re- sponse to the switchable capacitor(s) 30T being switched in or out, respectively, of the resonant network or tank 300.

In some embodiments and as shown, the switchable capacitor 30T is connected in parallel with at least one other capacitor 301 , 30T of the resonant network or tank 300. The at least one other capacitor may e.g. be a‘regular’ tank capacitor 301 , another switchable capacitor 30T, and/or any combinations thereof.

As disclosed herein, the resonant network or tank 300 may alternatively or in addi- tion be configured to selectively adjust its reactance in response to at least one switchable inductor (see e.g. 302’ in FIG. 3A - 3D) being switched in or out, respec- tively, of the resonant network or tank 300. In the shown resonant power converter 100, the inductor 302 is a positive imaginary impedance (Z_L = j w L_tank) that limits the current and therefore the impedance of the capacitor 301 , which is a negative imaginary impedance (Z_C = - 1 /(j w C_tank) ), will subtract from the inductor impedance resulting in a lower overall impedance of the resonant network or tank 300, which will limit the current less.

Due to this, it is therefore advantageous to have a capacitance that is as large as (feasibly) possible so that its impedance becomes insignificant (practically speaking) compared to the impedance of the inductor. Alternatively, the inductance of the tank inductor 301 should be increased in order to compensate for the negative capacitor impedance and obtain the desired effective inductance of the overall tank imped- ance. By selecting a relatively small capacitor, the inductor should have a relatively large compensation (e.g. having twice as much inductance than with a relatively larger capacitor). The effective inductance of the resonance tank (and thereby the resonance current magnitude and hence output power) can by controlled by switch- ing in (using a switch 125) in the switchable capacitor 30T (C_Tank3) in parallel with the initial small capacitor 301 (C_Tank), where the capacitance of 301 (C_Tank) is much smaller than the capacitance of 301’ (C_Tank3). Compared to FIG.1 the tank capacitor 301 (C_Tank) of the resonant network or tank 300 is shifted down to a ground connection and one or more switchable capacitors 30T (C_Tank3) is cou- pled in parallel with the tank capacitor 301 (C_Tank).

As an example, if the inductor is twice as large than required with a large tank ca- pacitor then the effective tank inductance can be changed to be twice as much by switching in a large (switchable) capacitor 30T (C_Tank3) in parallel to the tank ca- pacitor 301 (C_Tank). Doubling the current limiting inductance reduces the reso- nance current and the output power is roughly halve (about 50% of the full power output). Switching the switchable capacitor(s) 30T in a controllable manner provides an impedance control method with the advantages described above.

It is fairly simple to implement the solution according to FIG. 2A even when a trans- former is to be used in a resonant power converter 100 (see e.g. subsequent FIGs). The impedance control method mentioned above can also be used as a power modulation method. Instead of just having two discreet power levels, as in the above example, a pulse width modulation (PWM) control signal can be applied to the switch 125 (and also respectively to switch SW3 in FIGs 2B) - 2C) or switch M3 in FIGs 2D - 2E). The result of a 50% PWM control signal will be about 75% output power, as it is modulated between 50% and 100% output power. Several parallel capacitors and switches can be used (as indicated by the dashed lines in FIG. 2A) to achieve more and finer discrete impedance steps. The power modulation method is easily reflected to a secondary side of a transformer (see e.g. FIG. 2C) while maintaining the same functionality.

In some embodiments, the controllable switch arrangement 200 is a so-called pull- up and pull-down network or circuit. In some further embodiments, the controllable switch arrangement 200 is or comprises a resonant high frequency class DE inverter (as shown in FIG. 2A), which is one (more specific) example of a pull-up and pull- down network or circuit. However, according to aspects of the present invention, the resonator of the controllable switch arrangement 200 could be any kind of current outputting converter, with and without a transformer circuit (see e.g. some of the subsequent Figures and related description).

The skilled person will understand that the resonant power converter 100 may have any resonant power converter topology, for example a converter topology selected from a group of {class E, class F, class DE} or any converter topology derived there- from such as resonant SEPIC topology, resonant boost topology, class f₂ topology, LLC topology, or LCC topology.

FIG. 2B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 2A.

Shown in Fig. 2B is a resonant power converter 100 corresponding to the one in Fig. 2A (and embodiments thereof) except that the resonant power converter 100 of Fig. 2B comprises an isolation transformer 400 (for also simply denoted transformer).

The isolation transformer couples a primary side circuit and a secondary side circuit of the resonant power converter. In this particular exemplary embodiment, a primary or first side of the transformer 400 is coupled between an output of the tank inductor 302 (L_Tank) and the parallel capacitors 301 , 301’ while a secondary or second side of the transformer 400 is coupled between the load 1 15 and electrical ground.

Switching the at least one switchable capacitor 301’ in and out, respectively, chang- es the output voltage of the transformer 400 by changing the input (in the embodi- ment of Fig. 2B) voltage.

The transformer 400 provides, in this and other shown corresponding embodiments, galvanic isolation and/or impedance matching.

The transformer 400 in this and corresponding embodiments comprises a pair of magnetically coupled inductors comprising a first inductor electrically connected to the primary side circuit and a second inductor electrically connected to the output side circuit. The first and second inductors could be discrete windings both wound around a common magnetic permeable structure to form an isolation transformer. In alternative embodiments, the first and second inductors are integrated in a printed circuit board, or other suitable carrier material, without intervening magnetic materi- al.

FIG. 2C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 2B.

Shown in Fig. 2C is a resonant power converter 100 corresponding to the one in Fig. 2B (and embodiments thereof) except that the transformer 400 is now coupled with a primary or first side between an output of the tank inductor 302 (L_Tank) and elec- trical ground while a secondary or second side of the transformer 400 is coupled between the load 115 and the parallel capacitors 301 , 30T. Additionally, an addi- tional tank capacitor 301 (labelled C_Tank0) is coupled between the output of the controllable switch arrangement 200 and the input of the tank inductor 302

(L_Tank). The additional tank capacitor 301 (C_Tank0) is a DC-blocking capacitor (also forming part of the resonant network or tank 300). FIG. 2D) shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet an alternative embodiment of the resonant power converter of FIG. 2A.

Shown in Fig. 2D is a resonant power converter 100 corresponding to the one in Fig. 2B (and embodiments thereof) except that a different type of switch 125’ is used.

The switch 125’ of this Figure is a semiconductor switch (labelled M3).

In some embodiments, the semiconductor switch 125’ may comprise a transistor such as a MOSFET or IGBT, for example a Gallium Nitride (GaN) or Silicon Carbide (SiC) MOSFET.

FIG. 2E) shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet an alternative embodiment of the resonant power converter of FIG. 2B,

Shown in Fig. 2E is a resonant power converter 100 corresponding to the one in Fig. 2B (and embodiments thereof) except that a different type of switch 125’, namely a semiconductor switch 125’ (labelled M3), is used. The semiconductor switch 125’ may e.g. be of any of the types mentioned in connection with Fig. 2D.

FIG. 3A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with another embodiment of the invention.

Shown is a resonant high frequency power converter 100 according to an embodi- ment of the invention that comprises a controllable switch arrangement 200, a reso- nant network or tank 300, and a converter load 1 15. The power converter 100 could comprise any kind of current outputting power converter with or without a transform- er.

According to aspects of the present invention, the resonant network or tank 300 of Fig. 3A has an adjustable reactance and is configured to selectively adjust an in- ductance and/or a capacitance (in the shown embodiment adjusting only the induct- ance) of the resonant network or tank 300 thereby adjusting the reactance of the resonant network or tank 300. The inductance of the resonant network or tank 300 is selectively adjusted, at least in some embodiments, in response to a control signal. Adjusting the reactance adjusts the impedance of the resonant network or tank 300. In this way, impedance control is provided for a resonant power converter, and in particular a controlled power output is provided even when operating with variable and/or wide voltage input and/or output ranges.

In some embodiments, and as shown in FIG. 3A, at least one of the inductors 302 of the power converter 100 is a switchable inductor 302’ (labelled L_Tank4 in FIG. 3A) preferably, but not necessarily, connected to electrical ground. According to some embodiments, the resonant network or tank 300 is configured to selectively adjust its reactance in response to the switchable inductors(s) 302’ being switched in or out, respectively, of the resonant network or tank 300. Herein, an inductor 302 may also be referred to as a fixed inductor segment and a switchable inductor 302’ may also be referred to as a switchable inductor segment (302’).

In some embodiments and as shown, the switchable inductor 302’ is connected in series with at least one other inductor 302, 302’ of the resonant network or tank 300. The at least one other capacitor may e.g. be a‘regular’ tank capacitor 301 , another switchable capacitor 30T, and/or any combinations thereof.

As disclosed herein, the resonant network or tank 300 may alternatively or in addi- tion be configured to selectively adjust its reactance in response to at least one switchable capacitor (see e.g. 30T in Figs. 2A - 2E) being switched in or out, re- spectively, of the resonant network or tank 300.

The basic principle of the embodiment in this Figure is the same as in the embodi- ments shown and explained in connection with Figures 2A - 2E, i.e. controlling the effective inductance of the resonant network or tank 300. However, instead of changing the effective or overall capacitance of the the resonant network or tank 300 to affect the impedance, in this and corresponding embodiments, it is instead the effective or overall inductance of the resonant network or tank 300 that is changed by bypassing one or more (switchable) inductors 302’ of the resonant net- work or tank 300. It is fairly simple to implement the solution according to FIG. 3A even when a trans- former is to be used in a resonant power converter 100 (see e.g. subsequent FIGs). Compared to FIG.1 the tank inductor 302 (L_Tank3) of the resonant network or tank 300 is shifted down to a ground connection and one or more switchable inductors 302’ (L_Tank4) is coupled in series with the tank inductor 302 (L_Tank3). Each switchable inductor 302’ (L_Tank4) is controlled to be bypassed by closing its re- spective switch 125 (SW3).

As an example, if the inductors 302 (L_Tank3) and 302’ (L_Tank4) is of the same induct- ance, the output power is roughly halved (about 50% of the full power output) by halving both inductors in the resonance path (switch 125 (SW3) being turned off), and is at full power when 302’ (L_Tank4) is bypassed (switch 125 (SW3) being turned on).

Switching the switchable inductor(s) 302’ in a controllable manner provides an im- pedance control method with the advantages described above. Just like what was mentioned in connection with Fig. 2A, the impedance control method (for the reso- nant power converter shown in Fig.3A) can be used as a power modulation method. Again, several steps of switches can be used in order to achieve more and finer discrete impedance steps. The power modulation method is easily reflected to a secondary side of a transformer (e.g. like what was done in FIG. 2C) while maintain- ing the same functionality.

The controllable switch arrangement 200 and/or the load 1 15 may e.g. by of any one of the types respectively mentioned in connection with Fig. 2A.

As an example, the inductance of the inductor 302 (L_Tank3) may e.g. be 10 pH (micro Henry) and the inductance of the switchable inductor 302’ (L_Tank4) may e.g. be 20 pH. When the switch 125 (SW3) is open, the combined inductance of the inductors 302, 302’ (L_Tank3, L_Tank4) will be 30 pH. When the switch 125 (SW3) is closed - thereby bypassing the switchable inductor 302’ (L_Tank4) - the induct- ance will only be 10 pH. Thus, closing the switch 125 (SW3) will - in this example - cause a reduction of the combined inductance of the resonant network or tank 300 to about a third compared to when the switch 125 (SW3) is open.

FIG. 3B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3A.

Shown in Fig. 3B is a resonant power converter 100 corresponding to the one in Fig. 3A (and embodiments thereof) except that the resonant power converter 100 of Fig. 3B comprises a transformer 400. In this particular exemplary embodiment, a primary or first side of the transformer 400 is coupled between an output of the tank capaci- tor 301 (C_Tank) and the serially coupled inductors 302, 302’ while a secondary or second side of the transformer 400 is coupled between the load 1 15 and electrical ground.

Switching the at least one switchable inductor 302’ in and out, respectively, changes the output voltage of the transformer 400 by changing the input (in the embodiment of Fig. 3B) voltage.

The transformer 400 may be of any suitable type, e.g. as disclosed herein.

If the two or more tank inductors 302, 302’ is to be implemented on a same magnet- ic core of the transformer 400, it is preferred placing a further switch in series with the ground connection of the (or a) switchable inductor 302’ (L_Tank4), which should be switched off when the switch 125 (SW3) is on; otherwise the inductor 302 (L_Tank3) will act as short since the inductors are magnetically coupled. FIG. 3C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3A.

Shown in Fig. 3C is a resonant power converter 100 corresponding to the one in Fig. 2B (and embodiments thereof) except that a different type of switch 125’ is used and that a DC blocking capacitor 301 (C_Tank3) is coupled between the switch 125’ and a connection point between the inductors 302 (L_Tank3) and 302’ (L_Tank4). The switch 125’ of this Figure is a semiconductor switch (labelled M3), e.g. of the type mentioned in connection with Fig. 2D.

FIG. 3D shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3B.

Shown in Fig. 3D is a resonant power converter 100 corresponding to the one in Fig. 3B (and embodiments thereof) except that a different type of switch 125’ is used and that a DC blocking capacitor 301 (C_Tank3) is coupled between the switch 125’ and a connection point between the inductors 302 (L_Tank3) and 302’ (L_Tank4). The switch 125’ of this Figure is a semiconductor switch (labelled M3), e.g. of the type mentioned in connection with Fig. 2D.

FIG. 3E shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 3B.

Shown in Fig. 3E is a resonant power converter 100 corresponding to the one in Fig. 3B (and embodiments thereof) except that the the switch 125 (SW3), the tank induc- tor 302 (L_Tank), and the switchable inductor 302’ (L_Tank4) is coupled on a sec- ondary side of the transformer 400 (instead of the primary side as in Fig. 3B).

FIG. 4A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet another embodiment of the invention. Shown is a resonant high frequency power converter 100 according to an embodi- ment of the invention that comprises a controllable switch arrangement 200, a reso- nant network or tank 300, a transformer 400, and a converter load 115.

Illustrated is a resonant high-frequency class DE power converter 100 comprising a controllable switch arrangement 200, a resonant network (also sometimes referred to as tank, resonance tank, or similar) 300, and a converter load 115 (forth also equally referred to simply as load). The shown resonant power converter 100 is a class DE topology power converter as an example. However, the power converter 100 could comprise any kind of resonant converter comprising a transformer.

According to aspects of the present invention, the resonant network or tank 300 of Fig. 4A has an adjustable reactance and is configured to selectively adjust an in- ductance and/or a capacitance (in the shown embodiment adjusting (indirectly) only the inductance) of the resonant network or tank 300 thereby adjusting the reactance of the resonant network or tank 300. The inductance of the resonant network or tank 300 is selectively adjusted, at least in some embodiments, in response to a control signal. Adjusting the reactance adjusts the impedance of the resonant network or tank 300. In this way, impedance control is provided for a resonant power converter, and in particular a controlled power output is provided even when operating with variable and/or wide voltage input and/or output ranges.

In some embodiments (and as shown in FIG. 4A), the (indirectly adjustable) inductor 302’ (L_Tank) is a positive imaginary impedance (Z_L = j w L_tank) limiting the cur- rent and therefore the impedance of the capacitor 301 (C_Tank), which is a negative imaginary impedance (Z_C = - 1 /(j co C_tank) ), will subtract from the inductor im- pedance resulting in a lower overall impedance of the resonant network or tank 300, which will limit the current less.

The current across the inductor 302’ (L_Tank) is determined by the voltage across the inductor 302’ (L_Tank). As the input voltage 350 (V_S1 ) of the resonant power converter 100 varies then the voltage across the inductor 302’ (L_Tank) varies re- suiting in the current limit across it. By varying the effective transformer turns ratio, it is possible to control the voltage across the inductor 302’ (L_Tank) and consequent- ly the current to the load 115 at various input voltages 350 (V_S1 ). According to some embodiments, the resonant network or tank 300 is configured to selectively adjust its reactance in response to adjusting a turns ratio of the isolation transformer 400. In at least some embodiments, the transformer turns ratio is varied depending on an operating mode of the system, e.g. low or high input voltage range and/or in dependence of a desired power level (high or low). By changing the turns ratio of the transformer 400, the inductance of the inductor 302’ (L_Tank) (which is re- flected to the secondary side of the transformer 400) and load impedance is scaled, as the impedance seen by the resonant power converter 100 is the secondary side reactance reflected to the primary side, which is scaled by the square of the turns ratio. Consequently, the reactance of the resonant network or tank 300 is adjusted by adjusting a turns ratio of the isolation transformer 400.

That the resonant tank 302’ (L_Tank) is implemented on the rectifier side of the power converter 100 (secondary side of the transformer) entails that it is not necessary to change also the tank inductance value.

In at least some embodiments, the transformer turns ratio is changed or adjusted using one or more transformer taps of either the primary (as shown in Fig. 4A) or the secondary transformer winding. In such embodiments, the transformer 400 compris- es one or more taps at respective intermediate points 356 (where only one is shown in the Figure) on the winding (on either side depending on specific embodiment) for adjustment. Taps may e.g. be manually reconnected, or a manual or automatic switch (e.g. switch SW3 as in this exemplary embodiment) may be provided for changing between taps. The transformer taps may e.g. also be implemented as dis- crete separate windings. In effect, the taps (or other corresponding measures) allow for varying the effective transformer turns ratio thus providing scaling of the output load impedance and scaling of the inductance of the tank inductor 302’. The transformer comprises one or more taps for having two or more operating rang- es. The shown and corresponding embodiments enable having several operating ranges, each operating range requiring an additional transformer tap. Operation of the taps can be static (with the converter in off-state) or dynamic (with the converter running). Implementation of a number of operating ranges typically requires one additional switch plus N-switches, where N is the number of operating ranges. The embodiment of Fig. 4A has proven to be very efficient over entire system operating ranges.

As an example, the secondary side of the transformer (shown to the right in Fig. 4A) has 12 turns (with no tap(s)) and the primary side of the transformer has 36 turns with a tap located (at intermediate point 356) at 20 turns. Continuing the example, in a high input voltage range mode, switch SW3 should be open or off and switch SW4 should be closed or on. This would give - with the exemplary number of respective turns - a turns ratio of 36:12 or 3:1. In a low input voltage range mode, switch SW3 should be closed or on and switch SW4 should be open or off giving a turns ratio of 20:12 or approximately 2:1.

Accordingly, the reactance of the resonant network or tank is adjusted (depending on mode) by adjusting or changing the effective turns ratio of the transformer 400.

The power modulation is easily reflected to a secondary side of a transformer while maintaining the same functionality.

As the transformer turns are implemented on the same magnetic core, a switch (SW3, SW4) should be placed in both connections (i.e. between respective parts of the primary winding side and ground). Otherwise the shorted turns would result in the winding acting as a short since the turns are magnetically coupled.

FIG. 4B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention.

The embodiment of Fig. 4B correspond to the embodiment of Fig. 4A except that semiconductor switches 125’ (M3, M4) and DC blocking capacitors (C_Tank3, C_Tank4) are used instead of switches 125 (SW3, SW4) and instead of a capacitor 301 (C_Tank) coupled between the output of controllable switch arrangement 200 and the transformer 400, respectively, as described e.g. in connection with Fig. 3D and elsewhere. FIG. 5A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 4A.

Shown in Fig. 5A is a resonant power converter 100 corresponding to the one in Fig. 4A (and embodiments thereof) except that a leakage inductance of the transformer is used as part of a resonant tank, i.e. instead of using the (indirectly) adjustable inductor 302’ (L_Tank) of Fig. 4A, which thereby saves one component compared to the embodiment of Fig. 4A reducing implementation size and power consumption.

In at least some embodiments, the transformer turns ratio is varied depending on an operating mode of the system, e.g. low or high input voltage range and/or e.g. in dependence of a desired power level (high or low).

Like for the embodiments of Fig. 4A, the transformer turns ratio is, at least in some embodiments, changed or adjusted using (one or more) transformer taps at respec- tive turns of either the primary (e.g. as shown in Figs. 5A, B and C) or alternatively the secondary transformer winding (e.g. as shown in Figs. 5D and E). In such em- bodiments, the transformer 400 comprises (one or more) taps at intermediate points 356 on the winding (on either side of the transformer depending on specific embod- iment) for adjustment. According to the embodiment of Fig. 5A, the equivalent reso- nant tank (as implemented by the transformer leakage) as seen by the power con- verter is dependent on the selected transformer tap. As for the embodiment of Fig. 4A and corresponding ones, switches 125 SW3, SW4 are provided for changing between taps. Since the taps allow varying the resonant tank inductance and the effective transformer turns ratio as seen by the topology, scaling of the output power and of the output load impedance is readily provided.

The switches 125 (SW3, SW4) may alternatively e.g. be semiconductor switches as disclosed herein.

FIG. 5B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a more detailed implementation of the resonant power converter of FIG. 5A. Shown in Fig. 5B is a resonant power converter 100 corresponding to the one in Fig. 5A (and embodiments thereof) where at least two leakage inductances or leakage reactances 302, 302’ (designated L_Tank1 and L_Tank2) of the transformer 400 are used as a resonant tank.

In the shown embodiment, a non-switchable leakage inductance 302 L_Tank1 is connected in series with a tank capacitor 301 C_tank (connected to a controllable switch arrangement 200 as disclosed herein) and a first part or set of the windings 501 of the primary side of the transformer 400, where the (the other end of the) first part or set of the windings 501 of the primary side is connected with a tap or similar located at an intermediate point 356 of the primary windings of the transformer 400. The tap or similar is connected with a switch 125 (SW3) to an electrical reference potential such as electrical ground and to a switchable leakage inductance 302’ L_Tank2. The switchable leakage inductance 302’ L_Tank2 is connected (at the other end) with a second part or set of the windings 502 of the primary side of the transformer 400 where the second part or set 502 is connected at its other end via switch 125 (SW4) to the electrical reference potential, such as electrical ground. Switches 125 SW3, SW4 are used to control the resonant tank 300 by respectively selecting one of the resonant inductances 302, 302’ (L_Tank1 or L_Tank2), being integrated as transformer leakage, to be active (together with its respective first 501 or second 502 part or set of the primary side windings). In at least some embodiments, the effective transformer leakage inductance is var- ied (by switching in and out the respective resonant inductances L_Tank1 or L_Tank2) depending on the operating mode, e.g. via the switches 125 SW3, SW4 or other suitable arrangement, to control the resonant tank 300 depending on the op- erating mode of the system, e.g. low or high input voltage range and/or high or low output power. A first mode may e.g. be low input voltage with a second mode being high input voltage. Alternatively, a first mode may e.g. be low output power with a second mode being high output power. As a further example, in one operation mode (e.g. low input voltage range and/or high output power), the switch SW3 is closed and the switch SW4 is open whereby the resonant tank inductance is influenced by‘only’ the non-switchable leakage in- ductance 302 L_Tank1 and the first part or set of the windings 501 (in relation to the inductance of the secondary side), while in another operation mode (e.g. high input voltage range and/or low output power), the switch SW3 is open and the switch SW4 is closed whereby the resonant tank inductance is influenced by the non- switchable leakage inductance 302 L_Tank1 , the first part or set of the windings 501 , the switchable leakage inductance 302’ L_Tank2, and the second part or set of the windings 502 (in relation to the inductance of the secondary side).

As mentioned, the resonant power converter may readily support more than two operating modes by using additional taps (and thereby additional parts of the wind- ings), additional resonant inductances, and additional switches (one of each for each additional mode).

Accordingly, the controllability of the resonant power converter is improved as it is possible to control and regulate the output power and to achieve lower system loss- es. Another significant advantage is that the implementation size of the resonant power converter is reduced and a cost reduction thereof is achieved as one or more of the resonant elements fully is/are integrated in the transformer.

As indicated (by the three dashed lines under the symbol for the electrical reference potential), the resonant network or tank 300 may comprise more than one switcha- ble leakage inductances or reactances (i.e. then comprising two or more leakage inductances or reactances) by providing additional taps and switches (one of each for each additional switchable leakage inductance or reactance).

As an example, for a resonant power converter operating at 1 MHz, the first part or set of the windings 501 of the primary side of the transformer 400 may e.g. have 20 turns with an L_Tank1 302 value of about 10.6uH. The second part or set of the windings 502 of the primary side of the transformer 400 may e.g. have 16 turns with an L_Tank2 302’ value of about 6.6uH. L_Tank1 and L_Tank2 are magnetically coupled as they are part of the same magnetic circuit, so they cannot be directly summed. The secondary side windings 503 of the transformer 400 may e.g. have 12 turns (right side of Fig. 5B). Accordingly, the transformer will have an equivalent turns ratio of 20:12 (approximately 1.6:1 ) or 36:12 (approximately 3:1 ) depending on which switch is closed (SW3, SW4). Typical ratios between transformer magnetizing inductance 501 , 502 and respectively leakage inductance 302, 302’ can e.g. be se- lected from about 100:1 to about 2:1 depending on the magnetic circuit implementa- tion with about 10:1 being typical, at least for some certain implementations. Tank capacitor 301 C_Tank (as well as C_Tank3 and C_Tank4 of Fig. 5C) may e.g. be about 10nF.

Depending on the operating frequency of the system, the power levels, voltage lev- els, and/or values of the capacitances and inductances can vary. Generally, the higher the switching frequency, the lower the capacitances and inductances in the system.

FIG. 5C shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention.

The embodiment of Fig. 5C corresponds to the embodiment of Fig. 5B except that semiconductor switches 125’ (M3, M4) and DC blocking capacitors (C_Tank3, C_Tank4) are respectively used instead of switches 125 (SW3, SW4) and the ca- pacitor 301 (C_Tank) being coupled between the output of controllable switch ar- rangement 200 and the transformer 400. The switch semiconductor switches 125’ (M3, M4) may e.g. of the type mentioned in connection with Fig. 2D.

FIG. 5D shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 5B.

The embodiment of Fig. 5D corresponds to the embodiment of Fig. 5B except that the switches 125 (SW3, SW4) and the tank leakage inductances 302, 302’ (Ltankl , Ltank2) are coupled to the secondary side of the transformer 400 rather than the primary side as in Fig. 5B. Advantages of having these elements on the secondary side of the transformer 400 instead of on the primary side is e.g. that voltage and/or current ratings of the switches SW3, SW4 may be independent to the voltage and/or current ratings of the switches M1 , M2 of the controllable switch arrangement 200. Additionally, and depending on actual transformer design, it may be difficult to pro- vide one or more transformer taps on the primary side, whereby it may be beneficial to have the transformer tapping on the second side.

As an example, for a resonant power converter operating at 1 MHz, the primary side 503 of the transformer 400 has 36 turns (left side of Fig. 5D). The first part or set of the windings 501 of the secondary side of the transformer 400 may e.g. have 7 turns with an L_Tank1 302 value of about 1 uH. The second part or set of the windings 502 of the secondary side 502 of the transformer 400 may e.g. have 5 turns with an L_Tank2 302’ value of about 0.5uH. L_Tank1 and L_Tank2 are magnetically cou- pled as they are part or set of the same magnetic circuit, so they cannot be directly summed. Accordingly, the transformer will have an equivalent turns ratio of 36:7 and 36:12 depending on which switch (SW3, SW4) is closed. As mentioned, typical rati os between transformer magnetizing inductance 501 , 502 and respectively leakage inductance 302, 302’ can vary from about 100:1 to about 2:1 depending on the magnetic circuit implementation with about 10:1 being typical. Tank capacitor C_Tank 301 may e.g. be about 10nF (while C_Tank3 and C_Tank4 of Fig. 5E e.g. may be about 100nF). Depending on the operating frequency of the system, the power levels, the voltage levels, and/or values of the capacitances and inductances can vary. Again, generally, the higher the switching frequency the lower the capaci- tances and inductances in the system.

FIG. 5E shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention.

The embodiment of Fig. 5E correspond to the embodiment of Fig. 5C except that the switches 125’ (M3, M4), the tank leakage inductances 302, 302’ (L_Tank1 ,

L_Tank2), and the capacitors (C_Tank3, C_Tank4) are coupled to the secondary side of the transformer 400 rather than the primary side as in Fig. 5C with the addi- tion that the embodiment of Fig. 5E comprises a DC blocking capacitor C_Tank 301 coupled on the primary side of the transformer 400. This and corresponding embodiments, may have the same advantages as those given above for the embodiment of Fig. 5D in relation to the embodiment of Fig. 5B.

FIG. 6A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with yet another embodiment of the invention.

Shown is a resonant power converter 100 according to an embodiment of the inven- tion that comprises a controllable switch arrangement 200, a resonant network or tank 300, and a converter load 1 15. The power converter 100 could be any kind of resonant converter, with or without a transformer, where it is required to vary the impedance of resonant elements (which is similar to the embodiments shown and explained in connection with Figs. 2A - 2E and Figs. 3A - 3D).

The resonant network or tank 300 of Fig. 6A comprises a tank inductance 302’

(L ank) coupled to the load. The tank inductance 302’ (L_Tank) enables soft switching and controls the power flow between the half bridge and the load. By adding one or more windings to the resonant tank (auxiliary windings) it is possible to vary its equivalent impedance by connecting and disconnecting tuning capacitive elements 360 (C_Tune3, C_Tune4) via switches 125 (SW3, SW4) as illustrated. The switches can (as shown), but does not need to, have ground reference allowing simple driving circuitry. The tuning capacitors 360 (C_Tune3, C_Tune4) may have different values in or- der to achieve a large number of operating ranges while using few switches. Accord- ingly, an advantage is that this and corresponding embodiments, requires a mini- mum amount of switches even for large number of operating ranges. The number of operating ranges is equivalent to 2^N, where N is the number of switches. The equivalent resonant tank (transformer leakage) as seen from the half bridge is de- pendent on the switch configuration/state (on/off) of the switches 125 (SW3, SW4) switching the tuning capacitors 360 (C_Tune3, C_Tune4) in and out.

The switches 125 (SW3, SW4) and the auxiliary winding can be main ground refer- ence (as shown) thereby avoiding the need for high side gate drivers.

It is possible to actively control and modulate the switches 125 (SW3, SW4), e.g. using PWM as mentioned earlier. This and corresponding embodiments, enables control of the power flow by adjust- ing the tank inductance 302’ (L_Tank)· This and corresponding embodiments, uses one or more auxiliary windings on the tank inductance 302’ (L_Tank)·

A further advantage over the embodiments shown and explained in connection with Figs. 2A - 2E and Figs. 3A - 3D is that the load is not floating when not utilizing a transformer. Furthermore, this and corresponding embodiments, may be used for both isolated and non-isolated topologies.

When using a transformer with taps, operation of the tank taps can be static (with the converter in off-state) or dynamic (with the converter running).

FIG. 6B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 6A. Shown in Fig. 6B is a resonant power converter 100 corresponding to the one in Fig. 6A (and embodiments thereof) except that a different type of switches 125’, namely semiconductor switches 125’ (M3, M4), are used. The semiconductor switch 125’ may e.g. be of any of the types mentioned in connection with Fig. 2D. FIG. 7 shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 6A.

Shown is a resonant power converter 100 according to an embodiment of the inven- tion that comprises a controllable switch arrangement 200, a resonant network or tank 300, and a converter load 1 15. The power converter 100 could be any kind of resonant converter with a transformer. The shown power converter 100 (and em- bodiments thereof) corresponds to the power converter (and embodiments thereof) of Figs 6A - 6B but where the tuning capacitors is replaced with tuning inductors or any impedance component in generals.

The resonant network or tank 300 of Fig. 7 comprises a tank inductance 302’ (L_Tank) coupled to the load. The tank inductance 302’ L_Tank enables soft switching and con- trols the power flow between the half bridge and the load. By adding one or more windings to the resonant tank (auxiliary windings) it is possible to vary its equivalent impedance by connecting and disconnecting tuning inductive elements 370, 370’ (l__Tune3, L_Tune4) via switches 125 (SW3, SW4) as illustrated. The switches can (as shown), but does not need to, have ground reference allowing simple driving circuit- ry-

Generally, this power converter 100 has the same advantages as the power con- verter (and embodiments thereof) of Figs 6A - 6B. The tuning inductors (L_Tune3, l-_Tune4) may have different values in order to achieve a large number of operating ranges while using few switches.

FIG. 8A shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with a further embodiment of the invention.

Shown is a resonant high frequency class DE power converter 100 according to an embodiment of the invention that comprises a controllable switch arrangement 200, a resonant network or tank 300, and a converter load 115. The power converter 100 could be any kind of resonant power converter with or without a transformer.

Generally, a resonant is performing optimally in a design reference point, i.e. at the input/output voltage, chosen during design. Changing the output voltage will reflect directly on the performance, such as power and efficiency.

It is possible to compensate for the increased power loss when the input/output volt- age changes by adding one or more capacitor(s) 380 after the resonant network or tank 300. Preferably, the capacitance is chosen so it does not act as a short for the resonating current.

The capacitance can be implemented with one or more switches 125 in parallel (see e.g. 125/SW3, SW4 in Fig. 8A and 8B) to choose from different capacitance settings during operation or start-up thereby further improving the input/output range. The capacitance will counteract the change in impedance, induced by the changing out- put voltage. In a simplest implementation, the capacitor may just be added without the use of any switch. The switches 125 and capacitors may be relatively low volt- age switches as they only need to block the output voltage.

An advantage of this and corresponding embodiments is that losses over the output voltage range are decreased.

FIG. 8B shows a simplified schematic electrical circuit diagram of a resonant power converter in accordance with an alternative embodiment of the resonant power con- verter of FIG. 8A.

Shown in Fig. 8B is a resonant power converter 100 corresponding to the one in Fig. 8A (and embodiments thereof) except that the resonant power converter 100 of Fig. 8B comprises an isolation transformer 400 and that the one or more capacitor(s) added after the resonant network or tank 300 is coupled to a secondary side of the isolation transformer 400.

In the embodiment of Fig. 8C, a single capacitor 390 (C_out) is added across a full bridge rectifier 390. This may reduce the performance by a small amount in the op- timum point but reduces losses over a chosen output range.

Claims

1. A resonant power converter (100) comprising:

- an input side circuit comprising a positive and a negative input terminal for receipt of an input voltage,

- a controllable switch arrangement (200) configured to be driven by a switch control signal (355) to control a switching frequency of the resonant power converter (100),

- a resonant network or tank (300) coupled to an output of the controllable switch arrangement (200) to generate alternatingly increasing and decreas- ing resonant current in the resonant network or tank (300) in accordance with the switch control signal (355), the resonant network or tank (300) compris- ing at least one inductor (302, 302’) and at least one capacitor (301 , 301’), characterized in that

the resonant network or tank (300) comprises an adjustable reactance to change an impedance of the resonant network or tank (300), and wherein the adjustable reactance comprises at least one of an inductor with adjusta- ble inductance (302’) and a capacitor with adjustable capacitance (301’).

2. The resonant power converter (100) according to claim 1 , wherein the inductor comprises

- a fixed inductor segment (302) and a switchable inductor segment (302’) connected in series, and

a controllable switch configured to selectively connecting and disconnecting the switchable inductor segment (302’) from the resonant network to adjust the reactance of thereof.

3. The resonant power converter (100) according to claim 2, wherein the switchable inductor segment (302’) comprises a first end connected to the fixed inductor seg- ment and a second end connected to an electrical reference potential such as elec- trical ground, and

wherein the controllable switch is connected between the electrical reference poten- tial and the first end of the switchable inductor segment (302’).

4. The resonant power converter (100) according to claim 3, wherein the fixed induc- tor segment (302) comprises a first set of inductor windings and the switchable in- ductor segment (302’) comprises a second of inductor windings; said first and sec- ond sets of inductor windings being arranged on a common magnetic core.

5. The resonant power converter (100) according to any one of the preceding claims, further comprising an isolation transformer (400) coupling a primary side circuit and a secondary side circuit of the power converter.

6. The resonant power converter (100) according to claim 5, wherein the least one inductor (302) of the resonant network or tank (300) is arranged in the secondary side circuit and the at least one capacitor (301 ) is arranged in the primary side cir cuit.

7. The resonant power converter (100) according to claim 5 or 6, wherein the reso- nant power converter (100) is configured to adjust the reactance of the resonant network or tank (300) by adjusting a turns ratio of the isolation transformer (400).

8. The resonant power converter (100) according to any one of claim 1 - 7, wherein the resonant power converter (100) further comprising an isolation transformer (400) coupling a primary side circuit and a secondary side circuit of the power converter and wherein the isolation transformer (400) is configured to provide a leakage in- ductance as at least a part of the inductor with adjustable inductance.

9. The resonant power converter (100) according to any one of claims 1 - 4, where- in the resonant network or tank (300) comprises:

- an isolation transformer (400) coupling a primary side circuit and a second- ary side circuit of the power converter, the isolation transformer (400) corn- prising a first set of inductor windings (501 ) and a second set of inductor windings (502) arranged on a common magnetic core, a first leakage induct- ance (L_Tanki ) (302), and at least a second leakage inductance (L_Tank2) (302’), wherein - a first end of the first leakage inductance (L_Tanki) (302) is connected in series with a first end of the first set of inductor windings (501 ),

- a second end of the first set of inductor windings (501 ) is connected in series with a first end of the second leakage inductance (L_Tank2) (302’) at an inter- mediate point (356), and

- a second end of the second leakage inductance (302’) (L_Tank2) is connected in series with a first end of the second set of inductor windings (502), wherein the resonant power converter (100) or the resonant network or tank (300) is configured to selectively connect and disconnect the second leakage inductance (302’) (L_Tank2) and the second set of inductor windings (502) to and from, respective- ly, the resonant network or tank (300) to adjust the reactance of thereof.

10. The resonant power converter (100) according to claim 9, wherein the interme- diate point (356) and a second end of the second set of inductor windings (502) each is connected via a respective controllable switch (125, 125’) to an electrical reference potential such as electrical ground.

11. The resonant power converter (100) according to claim 9 or 10, wherein the at least one capacitor (301 ) is arranged in the primary side circuit of the isolation trans- former (400) and the at least one capacitor (301 ) is connected to

- a second end of the first leakage inductance (L_Tank1) (302), or

- to a primary winding (503) of the isolation transformer (400).

12. The resonant power converter (100) according to claim 9 or 10, wherein the at least one capacitor (301 ) comprises two capacitors (301 ) (C_Tank3; C_Tank4) where one of the two capacitors (301 ) (C_Tank3) is connected to the intermediate point (356) and the other of the two capacitors (301 ) (C_Tank4) is connected to a second end of the second set of inductor windings (502).

13. The resonant power converter (100) according to any one of claims 9 - 12, wherein the first set of inductor windings (501 ), the second set of inductor windings (502), the intermediate point (356), the first leakage inductance (L_Tanki) (302), and the at least a second leakage inductance (L_Tank2) (302’) are located in the primary side circuit of the isolation transformer (400), or alternatively are located in the sec- ondary side circuit of the isolation transformer (400).

14. The resonant power converter (100) according to any one of claim 1 - 4,

- wherein the resonant power converter (100) further comprising an isolation transformer (400) comprising a primary side and a secondary side,

- wherein the primary side is coupled between at least one capacitor (301 ) of the resonant network or tank (300) and a load (1 15), and

- wherein the secondary side is coupled between at least one switchable reac- tance element configured to adjust an inductance of the primary side, and wherein

- the resonant power converter (100) further comprises a plurality of switcha- ble tuning capacitive elements (360) arranged in parallel and each respec- tively being connected at a first end to the secondary side of the isolation transformer (400) and at a second end to an electrical reference potential such as electrical ground via a controllable switch (125, 125’),

or

- the resonant power converter (100) further comprises a fixed tuning inductive element (370) and a switchable tuning inductive element (370’) connected in series, and

a controllable switch (125, 125’) configured to selectively connecting and disconnecting the switchable tuning inductive element (370’) from the reso- nant network or tank (300) to adjust the reactance of thereof.

15. The resonant power converter (100) according to claim 1 - 14, wherein the res- onant power converter (100) comprises one or more further switchable capacitors (380) located between the resonant network or tank (300) and a load (115).

16. The resonant power converter (100) according to any one of claims 1 - 15, wherein the capacitor comprises a fixed capacitor segment (301 ) and a switchable capacitor segment (30T) connected in parallel;

a controllable switch configured to selectively connecting and disconnecting the switchable capacitor segment (301’) from the resonant network to adjust the reac- tance of thereof.

17. The resonant power converter (100) according to claim 7 or any one of claims 9

- 16, wherein the resonant power converter (100) is a resonant DCDC converter configured to adjust the impedance of the resonant network or tank (300) by adjust- ing the turns ratio of a primary side of the isolation transformer (400).

18. The resonant power converter (100) according to claim 7 or any one of claims 9

- 16, wherein the resonant power converter (100) is a resonant ACDC converter configured to adjust the impedance of the resonant network or tank (300) by adjust- ing the turns ratio of a primary side of the isolation transformer (400).

19. The resonant power converter (100) according to claim 7 or any one of claims 9

- 16, wherein the resonant power converter (100) is a resonant DCDC converter configured to adjust the impedance of the resonant network or tank (300) by adjust- ing the turns ratio of a secondary side of the isolation transformer (400).