TWI848563B - Flying-capacitor converter with zero-voltage switching - Google Patents

Abstract

A flying capacitor converter with zero-zero switching includes an input inductor, a fast-switching leg, a slow-switching leg, at least one flying capacitor, a resonant tank, and an output capacitor. The fast-switching leg included an upper leg having a plurality of upper switches and a lower leg having a plurality of lower switches. The upper leg and the lower leg are coupled at a first middle node, and the first middle node is coupled to the input inductor. Any two upper switches are coupled in series at an upper node and any two lower are coupled in series at a lower node. The slow-switching leg includes a slow-switching upper switch and a slow-switching lower switch, and the slow-switching upper switch and the slow-switching lower switch are coupled at a second middle node. The at least one flying capacitor is correspondingly coupled between the upper node and the lower node. The resonant tank includes a resonant inductor and a resonant capacitor, and the resonant inductor and the resonant capacitor are coupled in series between the first middle node and the second middle node. The output capacitor is coupled in parallel to the slow-switching leg.

Description

Stacked Capacitor Converter with Zero Voltage Switching

The present invention relates to a stacked capacitor converter, and more particularly to a stacked capacitor converter with zero voltage switching.

In recent years, high power density power factor corrector (PFC) often uses flying-capacitor converter (FC) to achieve higher power density and better efficiency. However, since the existing architecture cannot achieve zero-voltage switch (ZVS) switching, it is impossible to further improve power density and efficiency. In addition, circuit heat dissipation is also a major problem.

Therefore, how to design a stacked capacitor converter with zero-voltage switching, achieve zero-voltage switching of each switch by changing the switching frequency and resonant slots; or achieve a higher boost ratio by increasing the capacitor voltage level, so as to have the scalability of boost. Furthermore, the present invention can operate in DC-DC boost and buck, or form a totem pole type power factor corrector (PFC) to achieve power factor correction, or as an inverter. In addition, the integration and power density can be improved by coupling the input inductor and the resonant inductor, which is an important topic studied by the inventor of this case.

The purpose of the present invention is to provide a stacked capacitor converter with zero voltage switching to solve the problems of the prior art.

To achieve the above-mentioned purpose, the stacked capacitor converter with zero-voltage switching proposed in the present invention is used to receive input power and convert the input power into output power. The stacked capacitor converter includes an input inductor, a fast switching bridge arm, a slow switching bridge arm, at least one stacked capacitor, a resonant tank and an output capacitor. The first end of the input inductor receives the input power. The fast switching bridge arm has an upper bridge arm including a plurality of upper switches, and a lower bridge arm including a plurality of lower switches. A first end of the upper bridge arm and a first end of the lower bridge arm are coupled to a first midpoint, and the first midpoint is coupled to the second end of the input inductor. The upper switches are coupled in series to the upper contacts in pairs, and the lower switches are coupled in series to the lower contacts in pairs. The slow switching bridge arm includes a slow upper switch and a slow lower switch, and the slow upper switch and the slow lower switch are coupled to the second midpoint. At least one stacked capacitor is correspondingly coupled between the upper contact and the lower contact. The resonant tank has a resonant inductor and a resonant capacitor, and the resonant inductor and the resonant capacitor are coupled in series between the first midpoint and the second midpoint. The output capacitor is coupled in parallel to the slow switching bridge arm to provide an output power supply.

In one embodiment, the stacked capacitor converter provides a three-level output. The upper bridge arm includes two upper switches, namely a first upper switch and a second upper switch, and the first upper switch and the second upper switch are coupled to a first upper contact. The lower bridge arm includes two lower switches, namely a first lower switch and a second lower switch, and the first lower switch and the second lower switch are coupled to a first lower contact. The first upper switch and the first lower switch are coupled to a first midpoint. The number of the stacked capacitor is one, and it is coupled between the first upper contact and the first lower contact.

In one embodiment, the stacked capacitor converter provides a five-level output. The upper bridge arm includes four upper switches, namely, a first upper switch, a second upper switch, a third upper switch, and a fourth upper switch, and the first upper switch and the second upper switch are coupled to a first upper contact, the second upper switch and the third upper switch are coupled to a second upper contact, and the third upper switch and the fourth upper switch are coupled to a third upper contact. The lower bridge arm includes four lower switches, namely, a first lower switch, a second lower switch, a third lower switch, and a fourth lower switch, and the first lower switch and the second lower switch are coupled to a first lower contact, the second lower switch and the third lower switch are coupled to a second lower contact, and the third lower switch and the fourth lower switch are coupled to a third lower contact. The first upper switch and the first lower switch are coupled to a first midpoint. There are three stacked capacitors, namely a first stacked capacitor, a second stacked capacitor and a third stacked capacitor, and the first stacked capacitor is coupled between the first upper contact and the first lower contact, the second stacked capacitor is coupled between the second upper contact and the second lower contact, and the third stacked capacitor is coupled between the third upper contact and the third lower contact.

In one embodiment, the input inductor and the resonant inductor are an integrated coupling structure.

In one embodiment, the stacked capacitor converter operates in N phases. The N-phase stacked capacitor converter includes N sets of input inductors, N sets of fast switching bridge arms, N sets of at least one stacked capacitor, N sets of resonant tanks, a set of slow switching bridge arms, and a set of output capacitors.

In one embodiment, the input inductor of each phase is coupled to the resonant inductor of the corresponding resonant tank.

In one embodiment, two resonant inductors between two phases are cross-coupled.

In one embodiment, when the input power source and the output power source of the stacked capacitor converter are both DC power sources, the number of the resonant capacitor is one. The resonant capacitor is connected in series with the resonant inductor to form a series branch, and the first end of the series branch is coupled to the first midpoint, and the second end of the series branch is coupled to the second end of the upper bridge arm.

In one embodiment, the stacked capacitor converter operates when both the input power source and the output power source are DC power sources, and the number of the resonant capacitor is one. The resonant capacitor is connected in series with the resonant inductor to form a series branch, and the first end of the series branch is coupled to the first midpoint, and the second end of the series branch is coupled to the second end of the lower bridge arm.

In one embodiment, the stacked capacitor converter operates when both the input power source and the output power source are DC power sources, and the number of resonant capacitors is two, namely, a first resonant capacitor and a second resonant capacitor. The resonant inductor is coupled to the common point of the first resonant capacitor and the second resonant capacitor to form two branches, namely, a first branch and a second branch. The first end of the first branch is coupled to the first midpoint, and the second end of the first branch is coupled to the second end of the upper bridge arm. The first end of the second branch is coupled to the first midpoint, and the second end of the second branch is coupled to the second end of the lower bridge arm.

In one embodiment, the stacked capacitor converter operates when the input power is an AC power source and the output power is a DC power source, and the stacked capacitor converter includes two input inductors, two fast switching bridge arms, two stacked capacitors, a resonant tank and an output capacitor. The resonant tank is coupled between two first midpoints of the two fast switching bridge arms.

The proposed stacked capacitor converter with zero-voltage switching can achieve the following features and advantages: 1. The addition of an LC resonant tank enables the converter to have the function of full-switch zero-voltage switching, reducing switching losses and improving power conversion efficiency. 2. The addition of an LC resonant tank can accelerate the release of the energy stored in the parasitic capacitance of the switch, suppressing the surge during switch switching to protect the switch. 3. The input inductor current ripple is very small, so a smaller electromagnetic interference (EMI) level can be selected. The more levels the smaller the input inductor can be selected. 4. The number of stacked capacitors combined with switch switching can increase the cross-voltage types of the input inductor, so that the inductor can be charged and discharged with a smaller cross-voltage (dv/dt) at both ends. In this way, the ripple current is smaller due to the decrease in the inductor dv/dt, and the loss of the inductor is reduced. 5. Because the stacked capacitor level can be expanded, it has the scalability of level and boost ratio. 6. Through the resonance of the internal resonant tank, the parasitic capacitance of the switch to be turned on can be discharged during the switch dead time (dead time), so that it can achieve zero voltage turn-on. 7. Zero voltage switching reduces the heat dissipation requirements of the switch module. 8. Zero voltage switching increases the switching frequency and reduces the volume of magnetic components. 9. If the resonant inductor and input inductor are integrated by using coupled inductors, the advantage of magnetic flux cancellation can be obtained, which can improve efficiency and integration. 10. With coupled inductors, there is no additional magnetic component occupying volume.

In order to further understand the technology, means and effects adopted by the present invention to achieve the intended purpose, please refer to the following detailed description and drawings of the present invention. It is believed that the purpose, features and characteristics of the present invention can be understood in depth and in detail. However, the attached drawings are only provided for reference and explanation, and are not used to limit the present invention.

The technical content and detailed description of the present invention are described as follows with reference to the accompanying drawings.

Please refer to FIG. 1, which is a circuit diagram of the first embodiment of the stacked capacitor converter with zero voltage switching of the present invention. The stacked capacitor converter with zero voltage switching (hereinafter referred to as the stacked capacitor converter) of the present invention is used to input power Vin and convert the input power Vin into output power Vo. If the input power Vin is an AC power source, and the converted output power Vo is a DC power source, the stacked capacitor converter can be used as an AC-DC converter or a power factor corrector (PFC). However, this is not a limitation, which means that the stacked capacitor converter of the present invention can be used to convert different power types according to power requirements.

The stacked capacitor converter includes an input inductor Lboost, a fast switching bridge arm 11, a slow switching bridge arm 12, at least one stacked capacitor FC, a resonant tank 13 and an output capacitor Co.

The input inductor Lboost has a first end and a second end, and the first end of the input inductor Lboost receives the input power Vin. The fast switch bridge arm 11 has an upper bridge arm 111 and a lower bridge arm 112. The upper bridge arm includes a plurality of upper switches _Q11 , _Q12 , and the lower bridge arm 112 includes a plurality of lower switches _Q21 , _Q22 . The upper bridge arm 111 and the lower bridge arm 112 are coupled to a first midpoint N1, and the first midpoint N1 is coupled to the second end of the input inductor Lboost. The upper switches _Q11 , _Q12 are coupled in series to an upper contact N11 in pairs, and the lower switches _Q21 , _Q22 are coupled in series to a lower contact N21 in pairs. In this embodiment, the fast switching bridge arm 11 is coupled to the AC input power source Vin via an input inductor Lboost.

The slow switching bridge arm 12 includes a slow upper switch _Q1 and a slow lower switch _Q2 , and the slow upper switch _Q1 and the slow lower switch _Q2 are coupled to the second midpoint N2. In this embodiment, the slow switching bridge arm 12 is directly coupled to the AC input power Vin and is controlled by the mains frequency (ie, the frequency of the AC input power Vin).

At least one stacked capacitor FC is correspondingly coupled between the upper contact N11 and the lower contact N21. The resonant tank 13 has a resonant inductor Lr and a resonant capacitor Cr. The resonant inductor Lr and the resonant capacitor Cr are coupled in series between the first midpoint N1 and the second midpoint N2. The output capacitor Co is coupled in parallel to the slow switch bridge arm 12 to provide an output power Vo.

Please refer to FIG5, which is a circuit diagram of an inductive coupling embodiment of a stacked capacitor converter with zero voltage switching in a single-phase structure of the present invention. In this case, the input inductor Lboost and the resonant inductor Lr can be two separate inductors, two sets of coils (wound on two different cores), or the input inductor Lboost and the resonant inductor Lr can be an integrated coupling structure, that is, the input inductor Lboost and the resonant inductor Lr can share a core to achieve an integrated structure with a shared coupling magnetic path, as shown in FIG5.

Specifically, the embodiment shown in FIG. 1 is an example of a stacked capacitor converter providing a three-level output. Therefore, the upper bridge arm 111 includes two upper switches, namely, a first upper switch _Q11 and a second upper switch _Q12 , and the first upper switch _Q11 and the second upper switch _Q12 are coupled to a first upper contact N11. The lower bridge arm 112 includes two lower switches, namely, a first lower switch _Q21 and a second lower switch _Q22 , and the first lower switch _Q21 and the second lower switch _Q22 are coupled to a first lower contact N21. The first upper switch _Q11 and the first lower switch _Q21 are coupled to a first midpoint N1. The number of the stacked capacitor FC is one, and it is coupled between the first upper contact N11 and the first lower contact N21.

Please refer to FIG. 2, which is a circuit diagram of the second embodiment of the stacked capacitor converter with zero voltage switching of the present invention. The difference from FIG. 1 is that the embodiment shown in FIG. 2 uses a stacked capacitor converter to provide multi-level (N-level) output. Therefore, the number of switches of the upper bridge arm 111, the number of switches of the lower bridge arm 112, and the number of stacked capacitors FC are increased accordingly.

Taking the stacked capacitor converter providing a five-level output as an example, the upper bridge arm 111 includes four upper switches, namely a first upper switch _Q11 , a second upper switch _Q12 , a third upper switch _Q13 and a fourth upper switch _{Q14 ,} and the first upper switch _Q11 and the second upper switch _Q12 are coupled to a first upper contact N11, the second upper switch _Q12 and the third upper switch _Q13 are coupled to a second upper contact N12, and the third upper switch _Q13 and the fourth upper switch _Q14 are coupled to a third upper contact N13.

The lower bridge arm 112 includes four lower switches, namely a first lower switch Q ₂₁ , a second lower switch Q ₂₂ , a third lower switch Q ₂₃ and a fourth lower switch Q ₂₄ , and the first lower switch Q ₂₁ and the second lower switch Q ₂₂ are coupled to a first lower contact N21, the second lower switch Q ₂₂ and the third lower switch Q ₂₃ are coupled to a second lower contact N22, and the third lower switch Q ₂₃ and the fourth lower switch Q ₂₄ are coupled to a third lower contact N23.

The first upper switch _Q12 and the first lower switch _Q21 are coupled to the first midpoint N1. There are three stacked capacitors FC, namely the first stacked capacitor FC1, the second stacked capacitor FC2 and the third stacked capacitor FC3. The first stacked capacitor FC1 is coupled between the first upper connection point N11 and the first lower connection point N21, the second stacked capacitor FC2 is coupled between the second upper connection point N12 and the second lower connection point N22, and the third stacked capacitor FC3 is coupled between the third upper connection point N13 and the third lower connection point N23.

Incidentally, the implementation of stacked capacitor converters to provide more than five-level outputs is similar to the three-level and five-level architectures, so it will not be described in detail.

Please refer to FIG3, which is a circuit block diagram of a multi-phase parallel structure of a stacked capacitor converter with zero voltage switching of the present invention. Different from FIG1 and FIG2, the stacked capacitor converter with zero voltage switching of the present invention is applied to a single-phase structure, and the present invention can also realize the multi-phase parallel structure shown in FIG3. Specifically, as shown in FIG3, when the stacked capacitor converter is operated in N phases, the N-phase stacked capacitor converter includes N sets of input inductors Lboost, N sets of fast switching bridge arms 11, N sets of at least one stacked capacitor FC, N sets of resonant tanks 13, and a set of slow switching bridge arms 12 and a set of output capacitors Co.

In the multi-phase parallel structure shown in FIG3 , there are different types of inductive coupling. As shown in FIG4A , it is a circuit diagram of the first embodiment of inductive coupling in the multi-phase parallel structure of the stacked capacitor converter with zero voltage switching of the present invention. Specifically, the input inductance Lboost of each phase is coupled with the resonant inductance Lr of the corresponding resonant slot 13. Alternatively, as shown in FIG4B , it is a circuit diagram of the second embodiment of inductive coupling in the multi-phase parallel structure of the stacked capacitor converter with zero voltage switching of the present invention. Specifically, the two resonant inductances Lr between the two phases are cross-coupled.

As mentioned above, the resonant slot 13 (including the resonant inductor Lr and the resonant capacitor Cr) of the present invention can be used not only in AC-DC conversion circuits, but also in DC-DC conversion circuits. As shown in FIG. 6A to FIG. 6C, they are circuit diagrams of different embodiments of the resonant capacitor of the stacked capacitor converter with zero voltage switching of the present invention. As shown in FIG. 6A, when the stacked capacitor converter operates with the input power Vin as the DC power source V _DC and the output power Vo as the DC power source, the number of the resonant capacitor Cr is one. The resonant capacitor Cr is connected in series with the resonant inductor Lr to form a series branch, and a first end of the series branch is coupled to the first midpoint N1 (i.e., the common point of the first end of the upper bridge arm 111 and the first end of the lower bridge arm 112), and a second end of the series branch is coupled to the second lower switch _Q22 (i.e., the second end of the lower bridge arm 112).

As shown in FIG6B , when the stacked capacitor converter operates with the input power Vin as a DC power source V _DC and the output power Vo as a DC power source, the number of the resonant capacitor Cr is one. The resonant capacitor Cr is connected in series with the resonant inductor Lr to form a series branch, and the first end of the series branch is coupled to the first midpoint N1 (i.e., the common point of the first end of the upper bridge arm 111 and the first end of the lower bridge arm 112), and the second end of the series branch is coupled to the second upper switch _Q12 (i.e., the second end of the upper bridge arm 111).

As shown in FIG6C , when the stacked capacitor converter operates with the input power Vin being a DC power source V _DC and the output power Vo also being a DC power source, the number of resonant capacitors Cr is two, namely the first resonant capacitor Cr1 and the second resonant capacitor Cr2. The resonant inductor Lr is coupled to the common point of the first resonant capacitor Cr1 and the second resonant capacitor Cr2 to form two branches, namely the first branch and the second branch. The first end of the first branch is coupled to the first midpoint N1, and the second end of the first branch is coupled to the second upper switch Q ₁₂ (i.e., the second end of the upper bridge arm 111). The first end of the second branch is coupled to the first midpoint N1, and the second end of the second branch is coupled to the second lower switch Q ₂₂ (i.e., the second end of the lower bridge arm 112).

In addition to the aforementioned stacked capacitor converter being applicable (operated) in AC-DC conversion circuits and DC-DC conversion circuits, it can also be applied to DC-AC conversion circuits (i.e., inverter circuits). Please refer to FIG. 7 , which is a circuit diagram of the stacked capacitor converter with zero-voltage switching of the present invention applied to AC-DC conversion. The stacked capacitor converter operates when the input power Vin is an AC power source and the output power Vo is a DC power source. The stacked capacitor converter includes two input inductors Lboost-1, Lboost-2, two fast switching bridge arms 11-1, 11-2, two stacked capacitors FC-1, FC-2, a resonant tank 13 and an output capacitor Co. The first input inductor Lboost-1 is coupled to the first midpoint N1 of the first fast switching bridge arm 11-1, and the second input inductor Lboost-2 is coupled to the second midpoint N2 of the second fast switching bridge arm 11-2. The first stack capacitor FC-1 is coupled between the common point of the first upper switch _Q11 and the second upper switch _Q12 of the first fast switching bridge arm 11-1 and the common point of the first lower switch _Q21 and the second lower switch _Q22 ; the second stack capacitor FC-2 is coupled between the common point of the first upper switch _Q11 and the second upper switch _Q12 of the second fast switching bridge arm 11-2 and the common point of the first lower switch _Q21 and the second lower switch _Q22 . The resonant slot 13 is coupled between a first midpoint N1 of the first fast switching bridge arm 11 - 1 and a second midpoint N2 of the second fast switching bridge arm 11 - 2 .

In summary, the present invention can achieve a higher boost ratio by increasing the capacitor voltage level, and therefore has the scalability of boost. The zero-voltage switching of each switch is achieved by changing the switching frequency and the resonant slot. Furthermore, the present invention can operate in DC-DC boost and buck, or form a totem pole type power factor corrector (PFC) to achieve power factor correction, or as an inverter. In addition, the integration and power density can be improved by coupling the input inductor and the resonant inductor.

In summary, the present invention has the following features and advantages:

1. Adding LC resonance tank enables the full switch zero voltage switching function, reduces switching loss, and improves power conversion efficiency.

2. Adding an LC resonant tank can accelerate the release of the energy stored in the parasitic capacitance of the switch and suppress the surge during switch switching to protect the switch.

3. It has very small input inductor current ripple, so a smaller EMI level can be selected. The more levels it has, the smaller the input inductor can be selected.

4. The number of stacked capacitors combined with switch switching can increase the cross-voltage type of the input inductor, so that the inductor can be charged and discharged with a smaller cross-voltage (dv/dt) at both ends. In this way, since the inductor dv/dt decreases, the ripple current is smaller and the inductor loss is reduced.

5. Because the stacked capacitor level can be expanded, the voltage level and boost ratio are scalable.

6. Through the resonance of the internal resonant tank, the parasitic capacitance of the switch to be turned on can be discharged during the switching dead time, allowing it to achieve zero voltage conduction.

7. Zero voltage switching reduces the heat dissipation requirements of the switch module.

8. Zero voltage switching increases the switching frequency and reduces the size of magnetic components.

9. If the resonant inductor and input inductor are integrated using coupled inductors, the advantage of magnetic flux cancellation can be obtained, which can improve efficiency and integration.

10. With coupled inductors, no additional magnetic parts take up space.

The above description is only a detailed description and drawings of the preferred specific embodiments of the present invention, but the features of the present invention are not limited thereto, and are not used to limit the present invention. The entire scope of the present invention shall be subject to the following patent application scope. All embodiments that conform to the spirit of the patent application scope of the present invention and its similar variations shall be included in the scope of the present invention. Any changes or modifications that can be easily thought of by anyone familiar with the art within the field of the present invention can be covered by the following patent scope of this case.

Lboost: input inductor 11: fast switching bridge arm Lboost-1: first input inductor Lboost-2: second input inductor 11-1: first fast switching bridge arm 11-2: second fast switching bridge arm 12: slow switching bridge arm 13: resonant tank FC, FC1, FC2, FC3: stacked capacitor FC-1: first stacked capacitor FC-2: second stacked capacitor Co: output capacitor 111: upper bridge arm 112: lower bridge arm Q ₁₁ , Q ₁₂ , Q ₁₃ , Q ₁₄ : upper switch Q ₂₁ , Q ₂₂ , Q ₂₃ , Q ₂₄ : lower switch N1: first midpoint N2: second midpoint N11, N12, N13: upper contact N21, N22, N23: lower contact Q ₁ : Slow up switch Q ₂ : Slow down switch Lr: Resonance inductance Cr: Resonance capacitance Vin: Input power Vo: Output power

FIG. 1 is a circuit diagram of a first embodiment of a stacked capacitor converter with zero-voltage switching according to the present invention.

FIG. 2 is a circuit diagram of a second embodiment of the stacked capacitor converter with zero-voltage switching of the present invention.

FIG. 3 is a circuit block diagram of a multi-phase parallel structure of stacked capacitor converters with zero-voltage switching according to the present invention.

FIG. 4A is a circuit diagram of a first embodiment of the inductive coupling of a multi-phase parallel structure of stacked capacitor converters with zero voltage switching according to the present invention.

FIG. 4B is a circuit diagram of a second embodiment of the inductive coupling of a multi-phase parallel structure of stacked capacitor converters with zero voltage switching according to the present invention.

FIG. 5 is a circuit diagram of an inductive coupling embodiment of a stacked capacitor converter with zero voltage switching in a single-phase architecture according to the present invention.

FIG. 6A to FIG. 6C are circuit diagrams of different embodiments of the resonant capacitor of the stacked capacitor converter with zero-voltage switching of the present invention.

FIG. 7 is a circuit diagram of the stacked capacitor converter with zero voltage switching of the present invention applied to AC-DC conversion.

Lboost: input inductor

11: Quick switch bridge arm

12: Slow switching bridge arm

13: Resonance groove

FC: stacked capacitor

Co: output capacitance

111: Upper bridge arm

112: Lower bridge arm

Q ₁₁ , Q ₁₂ : upper switch

Q ₂₁ , Q ₂₂ : Lower switch

N1: First midpoint

N2: Second midpoint

N11: Upper contact

N21: Lower contact

Q ₁ : Slow on/off

Q ₂ : Slow down switch

Lr: resonant inductance

Cr: resonant capacitor

Vin: Input power

Vo: output power

Claims (8)

A stacked capacitor converter with zero voltage switching is used to receive an input power source, wherein the input power source is an AC power source, and convert the input power source into an output power source. The stacked capacitor converter includes: an input inductor, a first end of the input inductor receives the input power source; a fast switching bridge arm, having an upper bridge arm including a plurality of upper switches, and a lower bridge arm including a plurality of lower switches, a first end of the upper bridge arm and a first end of the lower bridge arm are coupled to a first midpoint, and the first midpoint is coupled to a second end of the input inductor; wherein the upper and lower bridge arms are connected to a first midpoint. The switches are coupled in series to an upper contact in pairs, and the lower switches are coupled in series to a lower contact in pairs; a slow switch bridge arm includes a slow upper switch and a slow lower switch, and the slow upper switch and the slow lower switch are coupled to a second midpoint; at least one stacked capacitor is coupled between the upper contact and the lower contact in correspondence; a resonant tank has a resonant inductor and a resonant capacitor, and the resonant inductor and the resonant capacitor are coupled in series between the first midpoint and the second midpoint; and an output capacitor is coupled in parallel to the slow switch bridge arm to provide the output power. A stacked capacitor converter with zero voltage switching as described in claim 1, wherein the stacked capacitor converter provides a three-level output; the upper bridge arm includes two upper switches, a first upper switch and a second upper switch, and the first upper switch and the second upper switch are coupled to a first upper contact; the lower bridge arm includes two lower switches, a first lower switch and a second lower switch, and the first lower switch and the second lower switch are coupled to a first lower contact; wherein the first upper switch and the first lower switch are coupled to the first midpoint; wherein the number of the stacked capacitor is one, and is coupled between the first upper contact and the first lower contact. A stacked capacitor converter with zero-voltage switching as described in claim 1, wherein the stacked capacitor converter provides a five-level output; the upper bridge arm includes four upper switches, namely a first upper switch, a second upper switch, a third upper switch and a fourth upper switch, and the first upper switch and the second upper switch are coupled to a first upper contact, the second upper switch and the third upper switch are coupled to a second upper contact, and the third upper switch and the fourth upper switch are coupled to a third upper contact; the lower bridge arm includes four lower switches, namely a first lower switch, a second lower switch, a third lower switch and a fourth lower switch, and the first lower switch is coupled to a first upper contact. The first lower switch is coupled to the second lower switch with a first lower contact, the second lower switch is coupled to the third lower switch with a second lower contact, and the third lower switch is coupled to the fourth lower switch with a third lower contact; wherein the first upper switch is coupled to the first lower switch with the first midpoint; wherein the number of the stacked capacitors is three, namely a first stacked capacitor, a second stacked capacitor and a third stacked capacitor, and the first stacked capacitor is coupled between the first upper contact and the first lower contact, the second stacked capacitor is coupled between the second upper contact and the second lower contact, and the third stacked capacitor is coupled between the third upper contact and the third lower contact. A stacked capacitor converter with zero-voltage switching as described in claim 1, wherein the input inductor and the resonant inductor are an integrated coupling structure. A stacked capacitor converter with zero voltage switching as described in claim 1, wherein the stacked capacitor converter operates in N phases; the N-phase stacked capacitor converter includes: N sets of the input inductors, N sets of the fast switching bridge arms, N sets of at least one stacked capacitor, N sets of the resonant tanks, and one set of the slow switching bridge arms and one set of the output capacitor. A stacked capacitor converter with zero-voltage switching as described in claim 5, wherein the input inductor of each phase is coupled to the resonant inductor of the corresponding resonant tank. A stacked capacitor converter with zero-voltage switching as described in claim 5, wherein two resonant inductors between two phases are cross-coupled. A stacked capacitor converter with zero voltage switching as described in claim 1, wherein the stacked capacitor converter operates when the input power source is an AC power source and the output power source is a DC power source, and the stacked capacitor converter includes: two input inductors, two fast switching bridge arms, two stacked capacitors, and a resonant tank and an output capacitor; wherein the resonant tank is coupled between the two first midpoints of the two fast switching bridge arms.

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