CN116111830A - A Half-Bridge-Full-Bridge Combined LLC Resonant DC Converter Based on Dual Transformers - Google Patents

Abstract

The embodiment of the invention discloses a half-bridge-full-bridge combined LLC resonant direct-current converter based on a double transformer, which comprises a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a fourth switching tube, a sixth switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a sixth switching tube, a first isolation transformer, a second isolation transformer and a filter inductor. On the basis of the full-bridge converter structure, a second transformer, a first capacitor and a second capacitor are added to form a half-bridge structure, the two structures adopt full-bridge rectifier circuits on the secondary side and share one pair of diodes, LC series connection is added to the non-homonymous end of the secondary side of the second transformer, and LLC resonance is formed with an excitation inductor. The invention has the characteristic of no current loss, can realize high-efficiency energy conversion in a wide input voltage range and realize the soft switching of the switching tube in a wide load range.

Description

A Half-Bridge-Full-Bridge Combined LLC Resonant DC Converter Based on Dual Transformers

technical field

The invention relates to the technical field of power electronics, in particular to a half-bridge-full-bridge combined LLC resonant DC converter based on double transformers.

Background technique

With the rapid development of power electronics technology, DC converters are an important part of electrical system power conversion and power transmission, and are widely used in auxiliary power fields such as communications, aerospace, transportation, and new energy charging. The LLC converter is widely used in the current DC converter. Compared with other DC converters, the LLC resonant converter has the advantages of high efficiency, high power density, and fewer switches. However, the traditional LLC resonant converter Converters usually have the following disadvantages: there is circulation loss on the primary side, and the switching frequency needs to be changed with the input voltage transformation, which is not conducive to the design of closed-loop control. The converter may run out of control under light load, and is not suitable for wide-range output.

Therefore, how to provide a solution to the above problems is a problem that those skilled in the art need to solve at present.

Contents of the invention

The technical problem to be solved by the embodiments of the present invention is to provide a half-bridge-full-bridge combined LLC resonant DC converter based on double transformers, which is used to solve the problem of realizing high-efficiency energy conversion in a wide input voltage range, and in a wide load range. The problem of realizing the soft switching of the switch tube.

In order to solve the above-mentioned technical problems, an embodiment of the present invention provides a half-bridge-full-bridge combined LLC resonant DC converter based on double transformers, including first to fourth switching tubes, first to fifth capacitors, first to The sixth rectifier diode, the first and second isolation transformers, and the resonant inductor, wherein the first and second capacitors are connected in parallel to the positive and negative output terminals of the DC power supply after being connected in series, and the positive and negative output terminals of the first and third switching tubes are connected in series connected in parallel to the positive and negative output terminals of the DC power supply, and the second and fourth switch tubes are connected in parallel to the positive and negative output terminals of the DC power supply after being connected in series; the non-identical terminal of the primary winding of the first transformer is connected to the first The three capacitors are connected in series with the connection points of the second and fourth switch tubes, and the terminals with the same name of the first transformer and the second transformer are connected with the connection points of the first switch tube and the third switch tube, The non-identical terminal of the second transformer is connected to the connection point of the first and second capacitors; the homonymous terminal of the secondary winding of the first transformer is connected to the anode of the first rectifier diode and the anode of the fourth rectifier diode. The cathode is connected, and the non-identical end is connected to the connection point of the same-named end of the secondary winding of the second transformer and is connected to the anode of the second rectifying diode and the cathode of the fifth rectifying diode, and the secondary winding of the second transformer The terminal with the same name is connected to the anode of the third rectifier diode and the cathode of the sixth rectifier diode after being connected in series with the resonant inductor and the fourth capacitor, the cathode of the first rectifier diode, the cathode of the second rectifier diode, the The cathode of the third rectifier diode is connected to one end of the filter capacitor, the other end of the fifth capacitor is connected to the anode of the fourth rectifier diode, the anode of the fifth rectifier diode, the sixth rectifier diode connected to the anode.

Implementing the embodiment of the present invention has the following beneficial effects: the present invention adopts the same control method as that of the phase-shifted full-bridge converter on the primary side of the transformer, and introduces a second transformer and a voltage divider circuit at the lagging bridge arm of the transformer to construct Out of the half-bridge topology, the LLC resonance is formed by series resonant capacitor and resonant inductor on the secondary side of the second transformer, which can eliminate the circulation loss of the primary side. Under the structure of only using the filter capacitor, the output ripple is reduced and the The power density of the converter, phase-shift control can make the LLC resonant circuit continue to work at the resonant operating point, improve the conversion efficiency, and realize zero-voltage switching in a wide load range, and work in a wide range of input voltage changes.

Description of drawings

Fig. 1 is a kind of overall circuit structure schematic diagram of the half-bridge-full bridge combined LLC resonant DC converter based on double transformer provided by the present invention;

Among them: V _in is the DC power supply, Q ₁ , Q ₂ , Q ₃ , and Q ₄ are the first to fourth switching tubes respectively, and C ₁ , C ₂ , C _r1 , C _r2 , and C _o are the first to fifth switching tubes respectively. Capacitors, T _r1 and T _r2 are the first and second transformers respectively, m _p and n _p are the primary windings of the first and second transformers respectively, m _s and n _s are the secondary windings of the first and second transformers respectively , D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ are the first to sixth rectifier diodes respectively, L _r is the resonant inductance, R is the load resistance;

Fig. 2 is a simplified equivalent circuit diagram of a half-bridge-full bridge combined LLC resonant DC converter based on double transformers provided by the present invention;

Fig. 3 is the schematic diagram of the main working waveform of Fig. 2 provided by the present invention;

4 to 9 are equivalent circuit diagrams of FIG. 2 in different modes provided by the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

Embodiments of the patent of the present invention are described in detail below, examples of which are shown in the drawings, and the following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments.

The circuit connection schematic diagram of the patent of the present invention is shown in Figure 1, a half-bridge-full bridge combined LLC resonant DC converter based on multiplexing of components, including first to fourth switching tubes, first to fifth capacitors, The first to sixth rectifier diodes, the first and second isolation transformers, and a resonant inductor.

Wherein, the first and second capacitors are connected in parallel to the positive and negative output terminals of the DC power supply after being connected in series, the first and third switch tubes are connected in parallel to the positive and negative output terminals of the DC power supply after being connected in series, and the second, The fourth switching tube is connected in parallel to the positive and negative output terminals of the DC power supply after being connected in series, and the non-identical end of the primary winding of the first transformer is connected in series with the third capacitor and connected to the connection point of the second and fourth switching tubes , the same-named end of the first transformer, the same-named end of the second transformer are connected to the series connection point of the first switch tube and the third switch tube, and the connection between the non-identical end of the second transformer and the first and second capacitors Click to connect.

The terminal with the same name of the secondary winding of the first transformer is connected to the anode of the first rectifier diode and the cathode of the fourth rectifier diode, and the terminal with the same name is connected to the terminal with the same name of the secondary winding of the second transformer. , the anode of the second rectifier diode and the cathode of the fifth rectifier diode are connected, and the non-identical terminal of the secondary winding of the second transformer is connected in series with the anode of the third rectifier diode after the resonant inductor and the fourth capacitor are connected in series , the cathode connection of the sixth rectifier diode. The cathode of the first rectifier diode, the cathode of the second rectifier diode, and the cathode of the third rectifier diode are connected to one end of the filter capacitor, and the other end of the fifth capacitor is connected to the fourth rectifier diode The anode of the diode, the anode of the fifth rectifier diode, and the anode of the sixth rectifier diode are connected, and the resistor is connected in parallel with the fifth capacitor.

In a specific embodiment of the patent of the present invention, Q ₁ and Q ₃ form a lagging bridge arm, Q ₂ and Q ₄ form a leading bridge arm, and Q ₂ and Q ₄ form a full bridge topology with transformer T _r1 and capacitors C ₁ and C ₂ , Q ₁ , Q ₃ , transformer T _r2 , capacitors C ₁ , C ₂ constitute a full-bridge topology, the secondary side adopts a full-bridge rectification structure, and LC is connected in series at the non-identical end of T _r2 transformer to form an LLC resonant circuit. By controlling the turn-on and turn-off timing of the four switching tubes on the primary side, an AC square wave voltage is obtained on the primary side of the transformer, and the energy is transferred to the output through the high-frequency transformer, thereby realizing the electrical isolation of the input and output. When the dead time is ignored, the conduction mode of the upper and lower switching tubes of the same bridge arm is 180° complementary conduction, but there is a phase difference between the driving signals of the switching tubes corresponding to the two bridge arms, which is called phase shifting horn. The converter adjusts the duty cycle of the rectified voltage on the secondary side by changing the phase shift angle between the leading bridge arm and the lagging bridge arm, thereby controlling the output voltage. In the DC converter control system, the magnitude of the phase shift angle is calculated by the difference between the output voltage and the reference voltage through a closed-loop controller (such as a proportional-integral-differential controller). In addition, the parasitic parameters of the device can be fully utilized through phase-shift control without additional additional components, creating conditions for the soft switching of the switching tube. The switching frequency of the switching tube is set equal to the LC series resonant frequency, and the circuit with the LC series resonant frequency as the switching frequency, the secondary diode can realize soft switching, which greatly reduces the switching loss generated when the circuit is switched. In addition, under this working condition, the gain of the circuit is 1, the on-resistance is the smallest, the commutation loss of the circuit is the smallest, and the energy conversion efficiency can reach the best. In the secondary side, the anodes of the six rectifier diodes are respectively connected to the two secondary windings of the T _r1 transformer and the T _r2 transformer, where the non-identical end of the T _r1 transformer and the same-name end of the T _r2 transformer share a pair of rectifier diodes, and the diodes The cathode is directly connected in parallel and connected to one end of the filter capacitor.

Below with the simplified equivalent circuit of accompanying drawing 2, in conjunction with accompanying drawing 3～8 narrate the concrete operating principle of the present invention. It can be seen from Figure 3 that the entire converter has 12 switching modes in one switching cycle, which are [t ₀ ~t ₁ ], [t ₁ ~t ₂ ], [t ₂ ~t ₃ ], [t ₃ ~t ₄ ], [t ₄ ~t ₅ ], [t ₅ ~t ₆ ], [t ₆ ~t ₇ ], [t ₇ ~t ₈ ], [t ₈ ~t ₉ ], [t ₉ ~t ₁₀ ] _{. _ _ _ _ _ _ _} A detailed analysis of the work situation.

To simplify the analysis, the following assumptions are made: 1) All devices are ideal devices; 2) The parasitic devices of the switch tube only consider the body diode and junction capacitance; 3) The transformer leakage inductance T _r2 is ignored; 4) Capacitor C ₁ and capacitor C ₂ Equivalent to a constant voltage source.

Switching mode 1 [t ₀ ~t ₁ ] (corresponding to Figure 4): Q ₁ , Q ₄ , D ₁ , and D ₆ are turned on, and after t ₀ , they enter the energy transmission stage, until t ₁ , they are turned off _Q4 . This period is a duty cycle period, the secondary side voltage is at a maximum value, and the secondary side resonant capacitor and resonant inductor resonate.

Switching mode 2 [t ₁ ~t ₂ ] (corresponding to Figure 5): At time t ₁ , Q ₄ is turned off, the secondary voltage of T _r1 transformer drops to 0, and the junction capacitance of Q ₄ and Q ₂ is in the inductive reactance Under the effect of linear charging and discharging, the primary and secondary currents begin to drop.

Switching mode 3 [t ₂ ~t ₃ ] (corresponding to Figure 6): At time t ₂ , the voltage across Q ₂ reaches 0, D ₂ turns on with zero voltage, D ₁ , D ₂ , and D ₃ are turned on, and T The voltage at both ends _{of r1} is clamped to zero potential by D ₁ and D ₂ , and the current i _fbpri of the bridge arm of the full bridge is reduced under the action of Cr1 to eliminate the circulation loss.

Switching mode 4 [t ₃ ~t ₄ ] (corresponding to Figure 7): at time t ₃ , when i _fbpri decreases to i _fbpri (t ₄ ), when T _r1 stops transmitting energy to the secondary side, D ₁ closes At this time, the secondary side transmits energy through the half-bridge arm.

Switching mode 5 [t ₄ ~t ₅ ] (corresponding to Figure 8): This period is called the non-duty cycle period. When the half-bridge arm current i _hbpri drops to i _hbpri (t ₅ ), Tr2 stops at this time Energy is transmitted to the secondary side, and D ₂ and D ₆ are turned off. The load is freewheeled by C _o .

Switching mode 6 [t ₅ ~t ₆ ] (corresponding to Figure 9): at time t ₅ , Q ₁ is turned off, at this time i _hbpri and if _bpri begin to increase in the opposite direction, and the junction of Q ₁ and Q ₃ The capacitor is linearly charged and discharged under the action of inductive reactance, the secondary side diodes D ₄ and D ₃ are turned on, and at time t ₆ , the voltage of Q ₃ is turned on.

The working principle of the second half cycle [t ₆ ~t ₁₂ ] is basically the same as that of the first half cycle [t ₀ ~t ₆ ], except that the current and voltage change in the opposite direction, so it will not be described further.

From the above description, it can be known that the half-bridge-full bridge combined LLC resonant DC converter proposed by the present invention based on component multiplexing has the following advantages: the converter can work in a wide range of input voltages, and all switching tubes can operate in a wide Soft switching is realized in a wide load range; the half-bridge and phase-shifted full-bridge hybrid structure greatly reduces the loss in circuit conversion and eliminates the phenomenon of primary side circulation loss; in addition, the simple phase-shift PWM control is used to adjust the output voltage, which is Helps simplify the design of magnetic components.

The above disclosure is only a preferred embodiment of the present invention, which certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (1)

1. The half-bridge-full-bridge combined LLC resonant direct-current converter based on the double transformers is characterized by comprising first to fourth switching tubes, first to fifth capacitors, first to sixth rectifier diodes, a first isolation transformer, a second isolation transformer and a resonant inductor, wherein the first and second capacitors are connected in series and then connected in parallel to positive and negative output ends of a direct-current power supply, the first and third switching tubes are connected in series and then connected in parallel to the positive and negative output ends of the direct-current power supply in a forward direction, the second and fourth switching tubes are connected in series and then connected in parallel to the positive and negative output ends of the direct-current power supply in the same direction, a non-homonymous end of a primary winding of the first transformer is connected with a connecting point of the second and fourth switching tubes after being connected in series with the third capacitor, the homonymous end of the first transformer and the homonymous end of the second transformer are connected with the connecting point of the first switching tube and the connecting point of the third switching tube, and the non-homonymous end of the second transformer is connected with the connecting point of the first and the second capacitor; the same-name end of the secondary winding of the first transformer is connected with the anode of the first rectifying diode and the cathode of the fourth rectifying diode, the non-same-name end of the secondary winding of the second transformer is connected with the connection point of the same-name end of the secondary winding of the second transformer and the anode of the second rectifying diode and the cathode of the fifth rectifying diode, the non-same-name end of the secondary winding of the second transformer is connected with the resonant inductor and the fourth capacitor in series and then is connected with the anode of the third rectifying diode and the cathode of the sixth rectifying diode, the cathode of the first rectifying diode, the cathode of the second rectifying diode and the cathode of the third rectifying diode are connected with one end of the filter capacitor, and the other end of the fifth capacitor is connected with the anode of the fourth rectifying diode, the anode of the fifth rectifying diode and the anode of the sixth rectifying diode.

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