A ZCT soft-switching DC / DC converter

Abstract

The present invention discloses a ZCT soft-switching DC / DC converter, comprising: a four-switch series main power bridge arm circuit, a passive auxiliary resonant circuit, a voltage and current commutation circuit, and an isolation rectification and filtering circuit. The main power bridge arm circuit is used for the transmission of input power supply energy; the passive auxiliary resonant circuit is used to cooperate with the working mode of the main power bridge arm circuit to eliminate the switching losses of two high-frequency power switching tubes that are mutually auxiliary switching tubes in the main power bridge arm circuit, and achieve zero-current soft switching; the commutation circuit is used for voltage and current phase switching; the isolation rectification and filtering circuit is used to rectify the voltage on the primary side, so as to output a smooth DC voltage. By using two high-frequency modulated power switching tubes as the main and auxiliary switching tubes of the output current in different quadrants, the present invention realizes zero-current soft switching of two high-frequency power switching tubes without increasing power switching devices, reduces switching losses, improves efficiency, helps to increase the working frequency of the system, and reduces the volume of the output filter.

Description

Technical Field

[0001] The present invention relates to a ZCT soft-switching DC / DC converter, belonging to the technical field of rectifiers in power conversion devices. Background Art

[0002] In recent years, the switching frequency of the switching tubes in DC / DC converters has been increasing. The advantage of increasing the switching frequency is that the volume of the filter elements of the converter can be greatly reduced, which is beneficial to improving the overall power density of the converter. It can also make the converter respond faster to load changes and improve the dynamic performance of the system. However, there is an inherent problem with the increase in the switching frequency of the switching tubes, that is, their switching process is hard switching, resulting in relatively large switching losses and electromagnetic interference. This will limit the working efficiency of the converter, making it inappropriate to set the switching frequency of the switching tubes in the converter too high. Therefore, soft-switching technology has become a research hotspot in recent years.

[0003] In terms of topological structure, methods for realizing soft switching include quasi-resonant technology, active clamping technology, and magnetic coupling-based technology, etc. For quasi-resonant technology, when the load changes greatly, the variation range of the switching frequency is very large, increasing the difficulty of designing passive devices. In the active clamping technology, there is a large circulating current in the auxiliary circuit, and a power switching tube specially designed for soft switching is added with relatively large switching stress. For the soft-switching scheme based on magnetic coupling technology, an auxiliary switching tube is also additionally introduced in its controllable auxiliary circuit, increasing the number of components. Therefore, it is necessary to propose a new type of converter topology to achieve zero-current (ZCT) soft switching without adding power switching devices. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a ZCT soft-switching DC / DC converter, with a passive auxiliary resonant circuit connected across the upper and lower parts of the four-switch series main power bridge arm, and a commutation circuit and an isolation rectification and filtering circuit are introduced at the same time, enabling two high-frequency modulated power switching tubes in the full-bridge topology of the main power bridge arm to be mutually auxiliary switching tubes, realizing zero-current soft switching of the two high-frequency power switching tubes, with relatively small switching stress of the switching tubes, and greatly reducing the switching losses.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] A ZCT soft-switching DC / DC converter, the DC / DC converter includes a four-switch series main power bridge arm circuit, a passive auxiliary resonant circuit, a voltage and current commutation circuit, an isolation rectification and filtering circuit, and a load resistor. Among them, the four-switch series main power bridge arm circuit includes two high-frequency power switching tubes that are mutually auxiliary switching tubes; a passive auxiliary resonant circuit is connected across the upper and lower parts of the four-switch series main power bridge arm circuit;

[0007] The four-switch series main power bridge arm circuit is connected to a passive auxiliary resonance circuit and a voltage-current commutation circuit for the transmission of input power supply energy;

[0008] The passive auxiliary resonance circuit is used to cooperate with the working mode of the four-switch series main power bridge arm circuit to eliminate the switching losses of two high-frequency power switches that are auxiliary switches to each other in the four-switch series main power bridge arm circuit and achieve zero-current soft switching;

[0009] The voltage-current commutation circuit is used for the switching of voltage and current phases and transmits them to the primary side of the coupling transformer in the isolation rectification and filtering circuit;

[0010] The isolation rectification and filtering circuit is used to rectify the voltage on the primary side of the coupling transformer to output a smooth DC voltage.

[0011] As a preferred solution of the present invention, the four-switch series main power bridge arm circuit includes a first to second high-frequency power switch, a first to second power-frequency power switch, and a first to second freewheeling diode; the first and second high-frequency power switches are auxiliary switches to each other;

[0012] The source of the first high-frequency power switch is connected to the drain of the first power-frequency power switch, the source of the first power-frequency power switch is connected to the drain of the second power-frequency power switch, and the source of the second power-frequency power switch is connected to the drain of the second high-frequency power switch;

[0013] The drain of the first high-frequency power switch and the cathode of the second freewheeling diode are respectively connected to the positive pole of the input voltage, and the source of the second power-frequency power switch and the drain of the second high-frequency power switch are respectively connected to the anode of the second freewheeling diode;

[0014] The source of the first high-frequency power switch and the drain of the first power-frequency power switch are respectively connected to the cathode of the first freewheeling diode, and the source of the second high-frequency power switch and the anode of the first freewheeling diode are respectively connected to the negative pole of the input voltage.

[0015] As a preferred solution of the present invention, the passive auxiliary resonance circuit includes an auxiliary resonance inductor and an auxiliary resonance capacitor; one end of the auxiliary resonance inductor is connected to the cathode of the first freewheeling diode, one end of the auxiliary resonance capacitor is connected to the anode of the second freewheeling diode, and the other end of the auxiliary resonance capacitor is connected to the other end of the auxiliary resonance inductor.

[0016] As a preferred solution of the present invention, the voltage-current commutation circuit includes a third to fourth power-frequency power switch; the source of the fourth power-frequency power switch is connected to the drain of the third power-frequency power switch, the drain of the fourth power-frequency power switch is connected to the positive pole of the input voltage, and the source of the third power-frequency power switch is connected to the negative pole of the input voltage.

[0017] As a preferred embodiment of the present invention, the isolation rectifier filter circuit includes a coupling transformer, an output capacitor, and third to fourth freewheeling diodes;

[0018] The source of the first power frequency power switch tube and the drain of the second power frequency power switch tube are respectively connected to the same-named ends of the primary side of the coupling transformer, and the drain of the third power frequency power switch tube and the source of the fourth power frequency power switch tube are respectively connected to the other end of the primary side of the coupling transformer;

[0019] The anode of the third freewheeling diode is connected to the same-named end of the secondary side of the coupling transformer, the cathode of the third freewheeling diode is connected to the cathode of the fourth freewheeling diode, and is also connected to one end of the output capacitor. The other end of the output capacitor is connected to the center tap of the secondary side of the coupling transformer, and the anode of the fourth freewheeling diode is connected to the other end of the secondary side of the coupling transformer;

[0020] The output capacitor is connected in parallel with the load resistor, and both ends of the load resistor are respectively connected to the positive and negative poles of the output voltage.

[0021] As a preferred embodiment of the present invention, when the current flowing through the primary side of the coupling transformer in the transformer is in the positive direction, the first high-frequency power switch tube is the main switch tube, the second high-frequency power switch tube is the auxiliary switch tube, the first freewheeling diode is the main power freewheeling diode, and the second freewheeling diode is the auxiliary diode; the converter has the following eleven operating modes:

[0022] Mode 1: The second high-frequency power switch tube is turned on in advance before the first high-frequency power switch tube is turned on. The third and first power frequency power switch tubes are turned on, and the fourth and second power frequency power switch tubes and the first high-frequency power switch tube are turned off. The current of the auxiliary resonant inductor resonates and rises in the positive direction, the voltage of the auxiliary resonant capacitor resonates and rises from a negative value, the current flowing through the same-named end of the primary side of the coupling transformer linearly decreases in the positive direction, the third freewheeling diode on the secondary side conducts, and the secondary side current flows through the output capacitor and the load resistor and then returns to the center tap of the coupling transformer;

[0023] Mode 2: The third and first power frequency power switch tubes are turned on, the current of the auxiliary resonant inductor continues to resonate in the reverse direction, and the parasitic diode of the second high-frequency power switch tube conducts. At this time, the voltage across the second high-frequency power switch tube is clamped to zero, completing zero-voltage turn-off. The fourth and second power frequency power switch tubes and the first high-frequency power switch tube are turned off. The voltage of the auxiliary resonant capacitor resonates and decreases from the positive maximum value, and the current flowing through the same-named end of the primary side of the coupling transformer transfers from the first freewheeling diode to the passive auxiliary resonant circuit and linearly decreases. The state of the secondary side is the same as that in Mode 1;

[0024] Mode 3: Turn on the first high-frequency power switch when the magnitude of the auxiliary resonant inductor current is equal to the current flowing through the same-name terminal of the primary side of the coupling transformer. The third and first power-frequency power switches are turned on, the parasitic diode of the second high-frequency power switch conducts, the fourth and second power-frequency power switches are turned off, the auxiliary resonant inductor current resonantly rises from a negative value, the auxiliary resonant capacitor voltage resonantly drops from zero, the current flowing through the same-name terminal of the primary side of the coupling transformer linearly rises, and the state of the secondary side is the same as that in Mode 1;

[0025] Mode 4: The third and first power-frequency power switches and the first high-frequency power switch are turned on, the fourth and second power-frequency power switches and the second high-frequency power switch are turned off, and the second freewheeling diode is turned on as an auxiliary diode at this time. The auxiliary resonant inductor current and the auxiliary resonant capacitor voltage change resonantly, the current flowing through the same-name terminal of the primary side of the coupling transformer linearly rises, and the state of the secondary side is the same as that in Mode 1;

[0026] Mode 5: The third and first power-frequency power switches and the first high-frequency power switch are turned on, the fourth and second power-frequency power switches and the second high-frequency power switch are turned off, no current passes through the passive auxiliary resonant circuit, the second freewheeling diode is turned off, the main power bridge arm circuit operates in the PWM mode, the current flowing through the same-name terminal of the primary side of the coupling transformer linearly rises, and the state of the secondary side is the same as that in Mode 1;

[0027] Mode 6: Turn on the second high-frequency power switch before turning off the first high-frequency power switch. The third and first power-frequency power switches are turned on, the fourth and second power-frequency power switches are turned off, the auxiliary resonant inductor current resonantly rises from zero, the auxiliary resonant capacitor voltage resonantly rises, the current flowing through the same-name terminal of the primary side of the coupling transformer linearly rises, and the state of the secondary side is the same as that in Mode 1;

[0028] Mode 7: After the auxiliary resonant inductor current drops to zero and continues to resonantly drop, the auxiliary resonant capacitor voltage resonantly drops from the maximum value, the parasitic diode of the second high-frequency power switch conducts, the voltage across the second high-frequency power switch is clamped at zero, the third and first power-frequency power switches and the first high-frequency power switch are turned on, the fourth and second power-frequency power switches are turned off, the current flowing through the same-name terminal of the primary side of the coupling transformer linearly rises, and the state of the secondary side is the same as that in Mode 1;

[0029] Mode 8: After the auxiliary resonant inductor current resonantly reverses to the current flowing through the same-name terminal of the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch is conducted, and the first high-frequency power switch is turned off with zero current and zero voltage. The third and first power-frequency power switches are turned on, the fourth and second power-frequency power switches are turned off, the current flowing through the same-name terminal of the primary side of the coupling transformer linearly rises, and the state of the secondary side is the same as that in Mode 1;

[0030] Mode 9: After the auxiliary resonant inductor current resonates reversely to the current flowing through the same-named terminal of the primary side of the coupled transformer, the parasitic diode of the first high-frequency power switch turns off naturally. The passive auxiliary resonant circuit supplies power to the secondary side with a constant current. The third and the first power frequency power switches are turned on, the first and the second high-frequency power switches, and the fourth and the second power frequency power switches are turned off. The state of the secondary side is the same as that in Mode 1;

[0031] Mode 10: The first freewheeling diode conducts. The current flowing through the same-named terminal of the primary side of the coupled transformer commutates from the passive auxiliary resonant circuit to the first freewheeling diode. The auxiliary resonant inductor current resonates reversely and rises, and the auxiliary resonant capacitor voltage resonates and drops. The third and the first power frequency power switches are turned on, the first and the second high-frequency power switches, and the fourth and the second power frequency power switches are turned off. The current flowing through the same-named terminal of the primary side of the coupled transformer linearly drops. The state of the secondary side is the same as that in Mode 1;

[0032] Mode 11: The current of the passive auxiliary resonant circuit is zero. At this time, the first freewheeling diode conducts. The third and the first power frequency power switches are turned on, the first and the second high-frequency power switches, and the fourth and the second power frequency power switches are turned off. The circuit operates in the PWM mode. The current flowing through the same-named terminal of the primary side of the coupled transformer linearly drops. The state of the secondary side is the same as that in Mode 1.

[0033] As a preferred embodiment of the present invention, when the current flowing through the primary side of the coupled transformer in the transformer is negative, the second high-frequency power switch is the main switch, the first high-frequency power switch is the auxiliary switch, the second freewheeling diode is the main power freewheeling diode, and the first freewheeling diode is the auxiliary diode; the converter has eleven operating modes.

[0034] The present invention adopts the above technical solutions and has the following technical effects compared with the prior art:

[0035] 1. The topology proposed by the present invention uses two high-frequency modulated power switches as the main and auxiliary switches of the output current in different quadrants, so as to realize the zero-current soft switching of the two high-frequency power switches without increasing the power switching devices, thereby reducing the switching loss, improving the overall efficiency of the converter, and suppressing the influence of electromagnetic interference.

[0036] 2. The topology proposed by the present invention can achieve full-wave rectification, further increase the switching frequency of the circuit, thereby reducing the volume of the output filter and improving the power density of the system.

[0037] 3. The present invention solves the problem of reverse recovery of the freewheeling diode on the primary side of the coupled transformer, which helps to reduce the stress of the switching device and improve the reliability and safety of the system; and the transformer can provide electrical isolation, which is helpful for preventing interference and protecting the circuit from voltage spikes. Description of the Drawings

[0038] Figure 1 is a schematic structural diagram of a ZCT soft-switching DC / DC converter of the present invention;

[0039] Figures 2(a) - 2(k) is a schematic diagram of the operating modes of each switch when the current flowing through the primary side of the coupled transformer of a ZCT soft-switching DC / DC converter of the present invention is positive;

[0040] Figures 3(a) - 3(k) is a schematic diagram of the operating modes of each switch when the current flowing through the primary side of the coupled transformer of a ZCT soft-switching DC / DC converter of the present invention is negative. Detailed Embodiment

[0041] The following describes in detail the embodiments of the present invention. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals indicate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention.

[0042] As Figure 1 shown, the present invention provides a ZCT soft-switching DC / DC converter, which includes a passive auxiliary resonant circuit connected across the upper and lower main power bridge arms, a four-switch series main power bridge arm circuit (where two high-frequency power switches S1 and S2 are auxiliary switches to each other), a voltage and current commutation circuit (commutation bridge arm), and an isolated rectifier and filter circuit. The single-pole double-frequency SPWM modulation method is adopted on the primary side.

[0043] The positive pole of the input power supply V i is connected to the drains of the first high-frequency power switch S1 of the main power bridge arm and the fourth power-frequency power switch Q2 of the commutation bridge arm, and at the same time is connected to the cathode of the second freewheeling diode D2. The negative pole of the input power supply V i is connected to the sources of the second high-frequency power switch S2 of the main power bridge arm and the third power-frequency power switch Q1 of the commutation bridge arm, and at the same time is connected to the anode of the first freewheeling diode D1. The source of the first high-frequency power switch S1 of the main power bridge arm is connected to one end of the auxiliary resonant inductor L r and the cathode of the first freewheeling diode D1, and at the same time is connected to the drain of the first power-frequency power switch Q L1 of the main power bridge arm. The drain of the second high-frequency power switch S2 of the main power bridge arm is connected to one end of the auxiliary resonant capacitor C r and the anode of the second freewheeling diode D2, and at the same time is connected to the source of the second power-frequency power switch Q L2 of the main power bridge arm. The other end of the auxiliary resonant inductor L r is connected to the auxiliary resonant capacitor C rAt the other end, the source electrode of the first power frequency power switch tube Q of the main power bridge arm L1 is connected to the source electrode of the second power frequency power switch tube Q of the main power bridge arm L2 and the drain electrode, and is also connected to the same-named end of the primary side of the coupling transformer T1. The drain electrode of the third power frequency power switch tube Q1 of the commutation bridge arm is connected to the source electrode of the fourth power frequency power switch tube Q2 of the commutation bridge arm, and is also connected to the other end of the primary side of the coupling transformer T1. The anode of the third freewheeling diode D3 is connected to the same-named end of the secondary side of the coupling transformer T1. The cathode of the third freewheeling diode D3 is connected to the cathode of the fourth freewheeling diode D4, and is also connected to the output capacitor C o and the load resistor R o At one end, the output capacitor C o and the load resistor R o At the other end are connected to the center tap of the secondary side of the coupling transformer T1. The anode of the fourth freewheeling diode D4 is connected to the other end of the secondary side of the coupling transformer T1.

[0044] The switching frequencies of the first power frequency power switch tube Q L1 and the second power frequency power switch tube Q L2 of the main power bridge arm, as well as the third power frequency power switch tube Q1 and the fourth power frequency power switch tube Q2 of the commutation bridge arm are all 50 Hz. The switching frequency range of the first high-frequency power switch tube S1 and the second high-frequency power switch tube S2 of the main power bridge arm is 100 kHz - 900 kHz. In this embodiment, 600 kHz is used for illustration.

[0045] In addition to the 4 classic PWM operating modes of the present invention ((1) The first high-frequency power switch tube S1, the power frequency power switch tube Q1 of the commutation bridge arm, and the power frequency power switch tube Q L1 of the main power bridge arm are turned on, and the input side supplies power to the output side; (2) The power frequency power switch tube Q1 of the commutation bridge arm and the power frequency power switch tube Q L1 of the main power bridge arm are turned on, and the first freewheeling diode D1 conducts freewheeling, and the input power supply is disconnected from the main circuit; (3) The second high-frequency power switch tube S2, the power frequency power switch tube Q2 of the commutation bridge arm, and the power frequency power switch tube Q L2 of the main power bridge arm are turned on, and the input side supplies power to the output side; (4) The power frequency power switch tube Q2 of the commutation bridge arm and the power frequency power switch tube Q L2 of the main power bridge arm are turned on, and the second freewheeling diode D2 conducts freewheeling, and the input power supply is disconnected from the main circuit.)), there are also an additional 18 operating modes, which are all indispensable links for realizing the soft switching of the high-frequency switch tubes.

[0046] The following takes Figure 1It is the main circuit structure. Considering that this main circuit topology has a certain symmetry, according to the different directions of the current flowing through the primary side of the coupling transformer, it is divided into two intervals: the positive and negative directions of the current flowing through the primary side of the coupling transformer. The specific working principle and working modes of the present invention will be described in combination with FIGS. 2-3.

[0047] Each working mode when the current flowing through the primary side of the coupling transformer is in the positive direction (in this mode, the first high-frequency power switch tube S1 of the main power bridge arm is the main switch tube, the second high-frequency power switch tube S2 of the main power bridge arm is the auxiliary switch tube, the first freewheeling diode D1 is the main power freewheeling diode, and the second freewheeling diode D2 is the auxiliary diode):

[0048] Working mode 1: As shown in Fig. 2(a), before the first high-frequency power switch tube S1 of the main power bridge arm is turned on, the second high-frequency power switch tube S2 is turned on in advance to create a zero-current turn-on condition for the first high-frequency power switch tube S1. The industrial frequency power switch tube Q1 of the commutation bridge arm and the industrial frequency power switch tube Q L1 are turned on, the industrial frequency power switch tube Q2 of the commutation bridge arm, the industrial frequency power switch tube Q L2 of the main power bridge arm and the first high-frequency power switch tube S1 of the main power bridge arm are turned off. The current i Lr of the auxiliary resonant inductor in the passive auxiliary resonant circuit resonates and rises in the positive direction, and the voltage v Cr of the auxiliary capacitor resonates and rises from a negative value (its absolute value resonates and decreases). The current i T flowing through the same-named end of the primary side of the coupling transformer linearly decreases in the positive direction. The third freewheeling diode D3 on the secondary side conducts, and the secondary side current flows through the output capacitor C o and the load resistor R o and then returns to the center tap of the coupling transformer.

[0049] Working mode 2: As shown in Fig. 2(b), the industrial frequency power switch tube Q1 of the commutation bridge arm and the industrial frequency power switch tube Q L1 of the main power bridge arm are turned on. The current i Lr of the auxiliary resonant inductor in the passive auxiliary resonant circuit resonates in the reverse direction. The parasitic diode of the second high-frequency power switch tube S2 of the main power bridge arm conducts. At this time, the voltage across the second high-frequency power switch tube S2 is clamped at zero to complete zero-voltage turn-off. The first high-frequency power switch tube S1 of the main power bridge arm, the industrial frequency power switch tube Q2 of the commutation bridge arm and the industrial frequency power switch tube Q L2 of the main power bridge arm are turned off. The voltage v Cr of the auxiliary capacitor resonates and decreases from the positive maximum value. The current i T flowing through the same-named end of the primary side of the coupling transformer transfers from the first freewheeling diode D1 to the auxiliary resonant branch and linearly decreases. The state on the secondary side is the same as that in working mode 1.

[0050] Working mode 3: As shown in Fig. 2(c), when the magnitude of the auxiliary inductor current is equal to the current flowing through the same-named terminal of the primary side of the coupling transformer, turn on the first high-frequency power switch tube S1 of the main power bridge arm. Since the inductor current cannot change suddenly, the first high-frequency power switch tube S1 of the main power bridge arm is turned on with zero current. The industrial frequency power switch tube Q1 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L1 are turned on. The parasitic diode of the second high-frequency power switch tube S2 of the main power bridge arm conducts. The industrial frequency power switch tube Q2 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L2 are turned off. The auxiliary resonant inductor current i Lr resonantly rises from a negative value, and the auxiliary capacitor voltage v Cr resonantly drops from zero. The current i flowing through the same-named terminal of the primary side of the coupling transformer T rises linearly, and the state of the secondary side is the same as that in working mode 1.

[0051] Working mode 4: As shown in Fig. 2(d), the first high-frequency power switch tube S1 of the main power bridge arm, the industrial frequency power switch tube Q1 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L1 are turned on. The second high-frequency power switch tube S2 of the main power bridge arm, the industrial frequency power switch tube Q2 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L2 are turned off. The second freewheeling diode D2 is turned on as an auxiliary diode at this time. The auxiliary resonant inductor current i Lr and the auxiliary capacitor voltage v Cr vary resonantly. The current i flowing through the same-named terminal of the primary side of the coupling transformer T rises linearly, and the state of the secondary side is the same as that in working mode 1.

[0052] Working mode 5: As shown in Fig. 2(e), the first high-frequency power switch tube S1 of the main power bridge arm, the industrial frequency power switch tube Q1 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L1 are turned on. The second high-frequency power switch tube S2 of the main power bridge arm, the industrial frequency power switch tube Q2 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L2 are turned off. No current passes through the passive auxiliary resonant circuit. The second freewheeling diode D2 is turned off. The main power circuit operates in the classic PWM mode. The current i flowing through the same-named terminal of the primary side of the coupling transformer T rises linearly, and the state of the secondary side is the same as that in working mode 1.

[0053] Working mode 6: As shown in Fig. 2(f), turn on the second high-frequency power switch tube S2 before turning off the first high-frequency power switch tube S1 of the main power bridge arm. The industrial frequency power switch tube Q1 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge arm L1 are turned on. The industrial frequency power switch tube Q2 of the commutation bridge arm and the industrial frequency power switch tube Q of the main power bridge armL2 Turn off, the current i of the auxiliary resonant inductor Lr Resonate from zero, the voltage v of the auxiliary capacitor Cr Resonate upward, the current i flowing through the same-named terminal of the primary side of the coupled transformer T Rise linearly, the state of the secondary side is the same as that in operating mode 1.

[0054] Operating mode 7: As shown in Fig. 2(g), the current i of the auxiliary resonant inductor Lr Continues to resonate downward after dropping to zero, the voltage v of the auxiliary capacitor Cr Resonates downward from the maximum value, the parasitic diode of the second high-frequency power switch tube S2 in the main power bridge arm conducts, the voltage across the second high-frequency power switch tube S2 is clamped to zero, and it can be turned off at zero voltage. The first high-frequency power switch tube S1 in the main power bridge arm, the industrial-frequency power switch tube Q1 in the commutation bridge arm, and the industrial-frequency power switch tube Q in the main power bridge arm L1 Turn on, the industrial-frequency power switch tube Q2 in the commutation bridge arm and the industrial-frequency power switch tube Q in the main power bridge arm L2 Turn off, the current i flowing through the same-named terminal of the primary side of the coupled transformer T Rise linearly, the state of the secondary side is the same as that in operating mode 1.

[0055] Operating mode 8: As shown in Fig. 2(h), the current i of the auxiliary resonant inductor Lr Resonates reversely until the current i flowing through the same-named terminal of the primary side of the coupled transformer T After that, the parasitic diode of the first high-frequency power switch tube S1 in the main power bridge arm is turned on, and the first high-frequency power switch tube S1 can be turned off at zero current and zero voltage. The industrial-frequency power switch tube Q1 in the commutation bridge arm and the industrial-frequency power switch tube Q in the main power bridge arm L1 Turn on, the industrial-frequency power switch tube Q2 in the commutation bridge arm and the industrial-frequency power switch tube Q in the main power bridge arm L2 Turn off, the current i flowing through the same-named terminal of the primary side of the coupled transformer T Rise linearly, the state of the secondary side is the same as that in operating mode 1.

[0056] Operating mode 9: As shown in Fig. 2(i), the current i of the auxiliary resonant inductor Lr Resonates reversely until the current i flowing through the same-named terminal of the primary side of the coupled transformer T After that, the parasitic diode of the first high-frequency power switch tube S1 in the main power bridge arm turns off naturally, and the auxiliary resonant branch supplies power to the secondary side with a constant current i T The industrial-frequency power switch tube Q1 in the commutation bridge arm and the industrial-frequency power switch tube Q in the main power bridge arm L1 Turn on, the first high-frequency power switch tube S1 in the main power bridge arm, the industrial-frequency power switch tube Q2 in the commutation bridge arm, the industrial-frequency power switch tube Q in the main power bridge arm L2When the second high-frequency power switch tube S2 of the main power bridge arm is turned off, the state on the secondary side is the same as that in operating mode 1.

[0057] Operating mode 10: As shown in Fig. 2(j), the first freewheeling diode D1 conducts, and the current i flowing through the same-named terminal of the primary side of the coupled transformer T commutates from the auxiliary resonant branch to the first freewheeling diode D1. The current i of the auxiliary resonant inductor Lr resonantly rises in the reverse direction, and the voltage v of the auxiliary capacitor Cr resonantly drops. The industrial-frequency power switch tube Q1 of the commutation bridge arm and the industrial-frequency power switch tube Q of the main power bridge arm L1 turn on. The first high-frequency power switch tube S1 of the main power bridge arm, the industrial-frequency power switch tube Q2 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L2 and the second high-frequency power switch tube S2 of the main power bridge arm turn off. The current i flowing through the same-named terminal of the primary side of the coupled transformer T linearly drops, and the state on the secondary side is the same as that in operating mode 1.

[0058] Operating mode 11: As shown in Fig. 2(k), the current of the resonant branch is zero. At this time, the first freewheeling diode D1 conducts, and the industrial-frequency power switch tube Q1 of the commutation bridge arm and the industrial-frequency power switch tube Q of the main power bridge arm L1 turn on. The first high-frequency power switch tube S1 of the main power bridge arm, the industrial-frequency power switch tube Q2 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L2 and the second high-frequency power switch tube S2 of the main power bridge arm turn off. The circuit operates in the classical PWM mode, and the current i flowing through the same-named terminal of the primary side of the coupled transformer T linearly drops, and the state on the secondary side is the same as that in operating mode 1.

[0059] Each operating mode with a negative current flowing through the primary side of the coupled transformer (in this mode, the second high-frequency power switch tube S2 of the main power bridge arm is the main switch tube, the first high-frequency power switch tube S1 of the main power bridge arm is the auxiliary switch tube, the second freewheeling diode D2 is the main power freewheeling diode, and the first freewheeling diode D1 is the auxiliary diode):

[0060] Operating mode 1: As shown in Fig. 3(a), the first high-frequency power switch tube S1 is turned on in advance before the second high-frequency power switch tube S2 of the main power bridge arm is turned on, creating a zero-current turn-on condition for the second high-frequency power switch tube S2. The industrial-frequency power switch tube Q2 of the commutation bridge arm and the industrial-frequency power switch tube Q of the main power bridge arm L2 turn on. The second high-frequency power switch tube S2, the industrial-frequency power switch tube Q1 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L1 turn off. The current i of the auxiliary resonant inductor in the passive auxiliary resonant circuit Lr resonantly rises in the positive direction, and the voltage v of the auxiliary capacitor CrRises from a negative resonance (its absolute value resonance decreases), and the current i flowing through the same-named terminal on the primary side of the coupling transformer T Decreases linearly in the reverse direction. The fourth freewheeling diode D4 on the secondary side conducts, and the current on the secondary side flows through the output capacitor C o And the load resistor R o And then returns to the center tap of the coupling transformer.

[0061] Operating mode 2: As shown in Fig. 3(b), the resonance inductance current i Lr Resonates through zero, causing the parasitic diode of the first high-frequency power switch tube S1 to conduct. The industrial-frequency power switch tube Q2 of the commutation bridge arm and the industrial-frequency power switch tube Q of the main power bridge arm L2 Turn on. The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the industrial-frequency power switch tube Q1 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L1 Turn off. The current i flowing through the same-named terminal on the primary side of the coupling transformer T Transfers from the second freewheeling diode D2 to the auxiliary resonance branch and decreases linearly in the reverse direction. The state on the secondary side is the same as that in operating mode 1.

[0062] Operating mode 3: As shown in Fig. 3(c), the current i flowing through the same-named terminal on the primary side of the coupling transformer T Completes the commutation process from the second freewheeling diode D2 to the auxiliary resonance branch. At this time, turning on the second high-frequency power switch tube S2 is zero-current turn-on. The current i flowing through the same-named terminal on the primary side of the coupling transformer T Starts to commutate from the auxiliary resonance branch to the second high-frequency power switch tube S2. The industrial-frequency power switch tube Q2 of the commutation bridge arm and the industrial-frequency power switch tube Q of the main power bridge arm L2 Turn on. The first high-frequency power switch tube S1, the industrial-frequency power switch tube Q1 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L1 Turn off. The current i flowing through the same-named terminal on the primary side of the coupling transformer T Rises linearly in the reverse direction. The state on the secondary side is the same as that in operating mode 1.

[0063] Operating mode 4: As shown in Fig. 3(d), the auxiliary resonance inductance current i Lr Passes through zero again, causing the first freewheeling diode D1 to conduct. The second high-frequency power switch tube S2, the industrial-frequency power switch tube Q2 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L2 Turn on. The first high-frequency power switch tube S1, the industrial-frequency power switch tube Q1 of the commutation bridge arm, and the industrial-frequency power switch tube Q of the main power bridge arm L1 Turn off. The current i flowing through the same-named terminal on the primary side of the coupling transformer T Rises linearly in the reverse direction. The state on the secondary side is the same as that in operating mode 1.

[0064] Working mode 5: As shown in Fig. 3(e), the second high-frequency power switch tube S2, the commutation leg industrial frequency power switch tube Q2, and the main power leg industrial frequency power switch tube Q L2 turn on, the first high-frequency power switch tube S1, the commutation leg industrial frequency power switch tube Q1, and the main power leg industrial frequency power switch tube Q L1 turn off, the circuit works in the classical PWM mode, and the current i flowing through the same-named terminal of the primary side of the coupling transformer T rises linearly in the reverse direction, and the state of the secondary side is the same as that in working mode 1.

[0065] Working mode 6: As shown in Fig. 3(f), before turning off the second high-frequency power switch tube S2, turn on the first high-frequency power switch tube S1 as an auxiliary switch tube, and the current i flowing through the same-named terminal of the primary side of the coupling transformer T starts to commutate from the second high-frequency power switch tube S2 to the auxiliary resonant branch. The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation leg industrial frequency power switch tube Q2, and the main power leg industrial frequency power switch tube Q L2 turn on, the commutation leg industrial frequency power switch tube Q1 and the main power leg industrial frequency power switch tube Q L1 turn off, and the current i flowing through the same-named terminal of the primary side of the coupling transformer T rises linearly in the reverse direction, and the state of the secondary side is the same as that in working mode 1.

[0066] Working mode 7: As shown in Fig. 3(g), the current of the auxiliary resonant inductor resonates through zero, which causes the parasitic diode of the first high-frequency power switch tube S1 to conduct, and it continues to resonate through the parasitic diode. The second high-frequency power switch tube S2, the commutation leg industrial frequency power switch tube Q2, and the main power leg industrial frequency power switch tube Q L2 turn on, the first high-frequency power switch tube S1, the commutation leg industrial frequency power switch tube Q1, and the main power leg industrial frequency power switch tube Q L1 turn off, and the current i flowing through the same-named terminal of the primary side of the coupling transformer T rises linearly in the reverse direction, and the state of the secondary side is the same as that in working mode 1.

[0067] Working mode 8: As shown in Fig. 3(h), the current i flowing through the same-named terminal of the primary side of the coupling transformer T completes the commutation from the second high-frequency power switch tube S2 to the auxiliary resonant branch, and the parasitic diode of the second high-frequency power switch tube S2 conducts, completing the zero-voltage and zero-current turn-off of the second high-frequency power switch tube S2. The commutation leg industrial frequency power switch tube Q2 and the main power leg industrial frequency power switch tube Q L2 turn on, the first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation leg industrial frequency power switch tube Q1, and the main power leg industrial frequency power switch tube Q L1Turn off, the current \(i\) flowing through the same - name terminal of the primary side of the coupling transformer T Increases linearly in the reverse direction, and the state of the secondary side is the same as that in operating mode 1.

[0068] Operating mode 9: As shown in Fig. 3(i), the constant - current of the auxiliary resonant branch discharges the output circuit, and the magnitude of the current is the same as the current \(i\) flowing through the same - name terminal of the primary side of the coupling transformer T Equal. The industrial - frequency power - switch tube Q2 of the commutation bridge arm and the industrial - frequency power - switch tube Q L2 Turn on. The first high - frequency power - switch tube S1, the second high - frequency power - switch tube S2, the industrial - frequency power - switch tube Q1 of the commutation bridge arm and the industrial - frequency power - switch tube Q L1 Turn off, and the state of the secondary side is the same as that in operating mode 1.

[0069] Operating mode 10: As shown in Fig. 3(j), the current \(i\) flowing through the same - name terminal of the primary side of the coupling transformer T Commutates from the auxiliary resonant branch to the second free - wheeling diode D2. The current \(i\) of the auxiliary resonant inductor Lr Resonantly rises from a negative value, and the voltage \(v\) of the auxiliary capacitor Cr Resonantly drops from zero. The industrial - frequency power - switch tube Q2 of the commutation bridge arm and the industrial - frequency power - switch tube Q L2 Turn on. The first high - frequency power - switch tube S1, the second high - frequency power - switch tube S2, the industrial - frequency power - switch tube Q1 of the commutation bridge arm and the industrial - frequency power - switch tube Q L1 Turn off. The current \(i\) flowing through the same - name terminal of the primary side of the coupling transformer T Decreases linearly in the reverse direction, and the state of the secondary side is the same as that in operating mode 1.

[0070] Operating mode 11: As shown in Fig. 3(k), the current \(i\) flowing through the same - name terminal of the primary side of the coupling transformer T Completes the commutation from the resonant branch to the second free - wheeling diode D2. The circuit operates in the classical PWM mode. The industrial - frequency power - switch tube Q2 of the commutation bridge arm and the industrial - frequency power - switch tube Q L2 Turn on. The first high - frequency power - switch tube S1, the second high - frequency power - switch tube S2, the industrial - frequency power - switch tube Q1 of the commutation bridge arm and the industrial - frequency power - switch tube Q L1 Turn off. The current \(i\) flowing through the same - name terminal of the primary side of the coupling transformer T Decreases linearly in the reverse direction, and the state of the secondary side is the same as that in operating mode 1.

[0071] As can be seen from the above, the present invention proposes a novel ZCT soft-switching DC / DC converter in which two high-frequency modulated power switching tubes in the full-bridge topology of the main power bridge arm are mutually auxiliary switching tubes. The zero-current switching of the power switching tubes is realized by connecting a passive auxiliary resonant circuit across the upper and lower parts of the main power bridge arm, reducing the switching loss of the system and suppressing the influence of electromagnetic interference.

[0072] The above embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. A ZCT soft-switching DC / DC converter, characterized in that, The DC / DC converter includes a four-switch series main power bridge arm circuit, a passive auxiliary resonance circuit, a voltage-current commutation circuit, an isolation rectification and filtering circuit, and a load resistor. The passive auxiliary resonance circuit is connected across the four-switch series main power bridge arm circuit. The four-switch series main power bridge arm circuit includes first to second high-frequency power switches, first to second power-frequency power switches, and first to second freewheeling diodes. The first and second high-frequency power switches are auxiliary switches to each other. The source of the first high-frequency power switch is connected to the drain of the first power-frequency power switch. The source of the first power-frequency power switch is connected to the drain of the second power-frequency power switch. The source of the second power-frequency power switch is connected to the drain of the second high-frequency power switch. The drain of the first high-frequency power switch and the cathode of the second freewheeling diode are respectively connected to the positive pole of the input voltage. The source of the second power-frequency power switch and the drain of the second high-frequency power switch are respectively connected to the anode of the second freewheeling diode. The source of the first high-frequency power switch and the drain of the first power-frequency power switch are respectively connected to the cathode of the first freewheeling diode. The source of the second high-frequency power switch and the anode of the first freewheeling diode are respectively connected to the negative pole of the input voltage. The passive auxiliary resonance circuit includes an auxiliary resonance inductor and an auxiliary resonance capacitor. One end of the auxiliary resonance inductor is connected to the cathode of the first freewheeling diode. One end of the auxiliary resonance capacitor is connected to the anode of the second freewheeling diode. The other end of the auxiliary resonance capacitor is connected to the other end of the auxiliary resonance inductor. The four-switch series main power bridge arm circuit is connected to the passive auxiliary resonance circuit and the voltage-current commutation circuit for the transmission of input power energy. The passive auxiliary resonance circuit is used to cooperate with the working mode of the four-switch series main power bridge arm circuit to eliminate the switching losses of the two high-frequency power switches that are auxiliary switches to each other in the four-switch series main power bridge arm circuit and achieve zero-current soft switching. The voltage-current commutation circuit is used for the switching of voltage and current phases and transmits them to the primary side of the coupling transformer in the isolation rectification and filtering circuit. The isolation rectification and filtering circuit is used to rectify the voltage on the primary side of the coupling transformer to output a smooth DC voltage.

2. The ZCT soft-switching DC / DC converter according to claim 1, characterized in that, The voltage-current commutation circuit includes third to fourth power-frequency power switches. The source of the fourth power-frequency power switch is connected to the drain of the third power-frequency power switch. The drain of the fourth power-frequency power switch is connected to the positive pole of the input voltage. The source of the third power-frequency power switch is connected to the negative pole of the input voltage.

3. The ZCT soft-switching DC / DC converter according to claim 2, characterized in that, The isolation rectification and filtering circuit includes a coupling transformer, an output capacitor, and third to fourth freewheeling diodes. The source of the first power-frequency power switch and the drain of the second power-frequency power switch are respectively connected to the same-named ends of the primary side of the coupling transformer. The drain of the third power-frequency power switch and the source of the fourth power-frequency power switch are respectively connected to the other end of the primary side of the coupling transformer. The anode of the third freewheeling diode is connected to the same-named terminal of the secondary side of the coupling transformer. The cathode of the third freewheeling diode is connected to the cathode of the fourth freewheeling diode and also connected to one end of the output capacitor. The other end of the output capacitor is connected to the center tap of the secondary side of the coupling transformer. The anode of the fourth freewheeling diode is connected to the other end of the secondary side of the coupling transformer; The output capacitor is connected in parallel with the load resistor. The two ends of the load resistor are respectively connected to the positive and negative poles of the output voltage.

4. The ZCT soft-switching DC / DC converter according to claim 3, wherein When the current flowing through the primary side of the coupling transformer in the transformer is in the forward direction, the first high-frequency power switch tube is the main switch tube, the second high-frequency power switch tube is the auxiliary switch tube, the first freewheeling diode is the main power freewheeling diode, and the second freewheeling diode is the auxiliary diode; The converter has the following eleven operating modes: Mode 1: The second high-frequency power switch tube is turned on in advance before the first high-frequency power switch tube is turned on. The third and first power frequency power switch tubes are turned on. The fourth and second power frequency power switch tubes and the first high-frequency power switch tube are turned off. The current of the auxiliary resonant inductor resonantly rises in the positive direction. The voltage of the auxiliary resonant capacitor resonantly rises from a negative value. The current flowing through the same-named terminal of the primary side of the coupling transformer linearly decreases in the positive direction. The third freewheeling diode on the secondary side conducts. The current on the secondary side flows through the output capacitor and the load resistor and then returns to the center tap of the coupling transformer; Mode 2: The third and first power frequency power switch tubes are turned on. The current of the auxiliary resonant inductor continues to resonate in the reverse direction. The parasitic diode of the second high-frequency power switch tube conducts. At this time, the voltage across the second high-frequency power switch tube is clamped to zero, completing zero-voltage turn-off. The fourth and second power frequency power switch tubes and the first high-frequency power switch tube are turned off. The voltage of the auxiliary resonant capacitor resonantly decreases from the positive maximum value. The current flowing through the same-named terminal of the primary side of the coupling transformer transfers from the first freewheeling diode to the passive auxiliary resonant circuit and linearly decreases. The state on the secondary side is the same as that in Mode 1; Mode 3: The first high-frequency power switch tube is turned on at the moment when the current of the auxiliary resonant inductor is equal to the current flowing through the same-named terminal of the primary side of the coupling transformer. The third and first power frequency power switch tubes are turned on. The parasitic diode of the second high-frequency power switch tube conducts. The fourth and second power frequency power switch tubes are turned off. The current of the auxiliary resonant inductor resonantly rises from a negative value. The voltage of the auxiliary resonant capacitor resonantly decreases from zero. The current flowing through the same-named terminal of the primary side of the coupling transformer linearly increases. The state on the secondary side is the same as that in Mode 1; Mode 4: The third and first power frequency power switch tubes and the first high-frequency power switch tube are turned on. The fourth and second power frequency power switch tubes and the second high-frequency power switch tube are turned off. The second freewheeling diode is turned on as an auxiliary diode at this time. The current of the auxiliary resonant inductor and the voltage of the auxiliary resonant capacitor change resonantly. The current flowing through the same-named terminal of the primary side of the coupling transformer linearly increases. The state on the secondary side is the same as that in Mode 1; Mode 5: The third and first power frequency power switch tubes and the first high-frequency power switch tube are turned on, the fourth and second power frequency power switch tubes and the second high-frequency power switch tube are turned off, no current passes through the passive auxiliary resonant circuit, the second freewheeling diode is turned off, the main power bridge arm circuit operates in the PWM mode, and the current flowing through the same-named terminal of the primary side of the coupling transformer rises linearly. The state of the secondary side is the same as that in Mode 1; Mode 6: Before turning off the first high-frequency power switch tube, turn on the second high-frequency power switch tube first. The third and first power frequency power switch tubes are turned on, the fourth and second power frequency power switch tubes are turned off. The current of the auxiliary resonant inductor resonantly rises from zero, the voltage of the auxiliary resonant capacitor resonantly rises, and the current flowing through the same-named terminal of the primary side of the coupling transformer rises linearly. The state of the secondary side is the same as that in Mode 1; Mode 7: After the current of the auxiliary resonant inductor drops to zero and continues to resonate and drop, the voltage of the auxiliary resonant capacitor resonantly drops from the maximum value. The parasitic diode of the second high-frequency power switch tube conducts, and the voltage across the second high-frequency power switch tube is clamped at zero. The third and first power frequency power switch tubes and the first high-frequency power switch tube are turned on, the fourth and second power frequency power switch tubes are turned off, and the current flowing through the same-named terminal of the primary side of the coupling transformer rises linearly. The state of the secondary side is the same as that in Mode 1; Mode 8: After the current of the auxiliary resonant inductor resonantly reverses to the current flowing through the same-named terminal of the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch tube is conducted, and the first high-frequency power switch tube is turned off with zero current and zero voltage. The third and first power frequency power switch tubes are turned on, the fourth and second power frequency power switch tubes are turned off, and the current flowing through the same-named terminal of the primary side of the coupling transformer rises linearly. The state of the secondary side is the same as that in Mode 1; Mode 9: After the current of the auxiliary resonant inductor resonantly reverses to the current flowing through the same-named terminal of the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch tube naturally turns off, and the passive auxiliary resonant circuit supplies power to the secondary side with a constant current. The third and first power frequency power switch tubes are turned on, the first and second high-frequency power switch tubes, and the fourth and second power frequency power switch tubes are turned off. The state of the secondary side is the same as that in Mode 1; Mode 10: The first freewheeling diode conducts, and the current flowing through the same-named terminal of the primary side of the coupling transformer commutates from the passive auxiliary resonant circuit to the first freewheeling diode. The current of the auxiliary resonant inductor resonantly reverses and rises, the voltage of the auxiliary resonant capacitor resonantly drops, the third and first power frequency power switch tubes are turned on, the first and second high-frequency power switch tubes, and the fourth and second power frequency power switch tubes are turned off, and the current flowing through the same-named terminal of the primary side of the coupling transformer drops linearly. The state of the secondary side is the same as that in Mode 1; Mode 11: The current of the passive auxiliary resonant circuit is zero. At this time, the first freewheeling diode conducts, the third and first power frequency power switch tubes are turned on, the first and second high-frequency power switch tubes, and the fourth and second power frequency power switch tubes are turned off. The four-switch tube series main power bridge arm circuit operates in the PWM mode, and the current flowing through the same-named terminal of the primary side of the coupling transformer drops linearly. The state of the secondary side is the same as that in Mode 1.

5. The ZCT soft-switching DC / DC converter according to claim 3, wherein, When the current flowing through the primary side of the coupling transformer in the transformer is negative, the second high-frequency power switch is the main switch, the first high-frequency power switch is the auxiliary switch, the second freewheeling diode is the main power freewheeling diode, and the first freewheeling diode is the auxiliary diode; the converter has eleven operating modes.

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