ZCT soft switching DC / DC converter

Abstract

The invention discloses a ZCT soft switching DC / DC converter, which comprises a four-switch tube series main power bridge arm circuit, a passive auxiliary resonance circuit, a voltage and current commutation circuit and an isolation rectification filter circuit, and is characterized in that the main power bridge arm circuit is used for transmitting input power energy; the passive auxiliary resonance circuit is used for cooperating with the working mode of the main power bridge arm circuit, eliminating the switching loss of two high-frequency power switch tubes which are auxiliary switch tubes for each other in the main power bridge arm circuit, and achieving zero-current soft switching. The commutation circuit is used for voltage and current phase switching; the isolation rectification filter circuit is used for rectifying the voltage of the primary side so as to output smooth DC voltage. The two high-frequency modulated power switch tubes serve as main and auxiliary switch tubes of output current in different quadrants, zero-current soft switching of the two high-frequency power switch tubes is achieved on the basis that power switch devices are not increased, switching loss is reduced, efficiency is improved, the working frequency of a system is improved, and the system reliability is improved. The size of the output filter is reduced.

Description

Technical Field

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

[0002] In recent years, the operating frequency of the switch tube of the DC / DC converter has been getting higher and higher. The advantage of the increased operating frequency is that the volume of the converter filter element can be greatly reduced, which is conducive to improving the overall power density of the converter, and can also make the converter respond faster to load changes, improving the dynamic performance of the system. However, there is an inherent problem with the increase in the operating frequency of the switch tube, that is, its switching process is a hard switch, which leads to large switching losses and electromagnetic interference, which will limit the working efficiency of the converter, so that the operating frequency of the switch tube in the converter should not be too high. Therefore, soft switching technology has become a hot research topic in recent years.

[0003] In terms of topology, methods for achieving soft switching include quasi-resonant technology, active clamping technology, and technology based on magnetic coupling. For quasi-resonant technology, when the load changes significantly, the switching frequency varies greatly, which increases the difficulty of passive device design. In the auxiliary circuit of active clamping technology, there is a large circulating current, and a power switch tube designed for soft switching is added, and the switch stress is large. For the soft switching scheme based on magnetic coupling technology, auxiliary switch tubes are also introduced in the controllable auxiliary circuit, which increases the number of components. Therefore, it is necessary to propose a new 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, in which a passive auxiliary resonant circuit is connected across the upper and lower main power bridge arms of four switches in series, and a phase switching circuit and an isolation rectifier filter circuit are introduced at the same time, so that the two high-frequency modulated power switch tubes in the full-bridge topology of the main power bridge arm are auxiliary switch tubes to each other, thereby realizing zero-current soft switching of the two high-frequency power switch tubes, with less stress on the switch tubes and greatly reducing 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 comprising a four-switch tube series main power bridge arm circuit, a passive auxiliary resonant circuit, a voltage and current commutation circuit, an isolation rectifier filter circuit and a load resistor, wherein the four-switch tube series main power bridge arm circuit comprises two high-frequency power switch tubes that are auxiliary switch tubes to each other; the four-switch tube series main power bridge arm circuit is connected with a passive auxiliary resonant circuit above and below;

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

[0008] The passive auxiliary resonant circuit is used to cooperate with the working mode of the four-switch tube series main power bridge arm circuit, eliminate the switching loss of two high-frequency power switch tubes that serve as auxiliary switch tubes to each other in the four-switch tube series main power bridge arm circuit, and realize zero-current soft switching;

[0009] The voltage-current phase-changing circuit is used to switch the voltage and current phases and transmit 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, thereby outputting a smooth direct current voltage.

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

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

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

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

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

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

[0017] As a preferred solution of the present invention, the isolation rectification and filtering 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-name terminal on 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 connected to one end of the output capacitor at the same time, the other end of the output capacitor is connected to the center tap on the secondary side of the coupling transformer, and the anode of the fourth freewheeling diode is connected to the other end on 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 connected to the positive and negative poles of the output voltage respectively.

[0021] As a preferred solution of the present invention, 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 working 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 industrial frequency power switch tubes are turned on, the fourth and second industrial frequency power switch tubes and the first high-frequency power switch tube are turned off, the auxiliary resonant inductor current rises in the positive direction, the auxiliary resonant capacitor voltage rises from the negative value resonance, the current flowing through the same-name terminal on the primary side of the coupling transformer decreases linearly in the positive direction, the third freewheeling diode on the secondary side is turned on, 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 industrial frequency power switch tubes are turned on, the auxiliary resonant inductor current continues to resonate in the opposite direction, the parasitic diode of the second high-frequency power switch tube is turned on, and the voltage across the second high-frequency power switch tube is clamped at zero, completing the zero voltage shutdown. The fourth and second industrial frequency power switch tubes and the first high-frequency power switch tube are turned off, and the auxiliary resonant capacitor voltage drops from the positive maximum value resonance. The current flowing through the same-name end of the primary side of the coupling transformer is transferred from the first freewheeling diode to the passive auxiliary resonant circuit, and decreases linearly. The state of the secondary side is consistent with Mode 1.

[0024] Mode 3: When the auxiliary resonant inductor current is equal to the current flowing through the same-name terminal on the primary side of the coupling transformer, the first high-frequency power switch tube is turned on, the third and first industrial frequency power switch tubes are turned on, the parasitic diode of the second high-frequency power switch tube is turned on, the fourth and second industrial frequency power switch tubes are turned off, the auxiliary resonant inductor current rises from negative resonance, the auxiliary resonant capacitor voltage drops from zero resonance, the current flowing through the same-name terminal on the primary side of the coupling transformer rises linearly, and the state of the secondary side is consistent with mode 1;

[0025] Mode 4: The third and first industrial frequency power switch tubes and the first high frequency power switch tube are turned on, the fourth and second industrial frequency power switch tubes and the second high frequency power switch tube 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 in resonance, and the current flowing through the same-name terminal on the primary side of the coupling transformer increases linearly. The state of the secondary side is consistent with Mode 1.

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

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

[0028] Mode 7: After the auxiliary resonant inductor current drops to zero, it continues to resonate and drop, the auxiliary resonant capacitor voltage drops from the maximum value, the parasitic diode of the second high-frequency power switch tube is turned on, 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-name terminal on the primary side of the coupling transformer increases linearly. The state of the secondary side is consistent with mode 1.

[0029] Mode 8: After the auxiliary resonant inductor current reversely resonates to the current flowing through the same-name end of the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch tube is turned on, the first high-frequency power switch tube is turned off by 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-name end of the primary side of the coupling transformer rises linearly, and the state of the secondary side is consistent with mode 1;

[0030] Mode 9: After the auxiliary resonant inductor current reversely resonates to the current flowing through the same-name terminal on the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch tube is naturally turned 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, and the state of the secondary side is consistent with Mode 1.

[0031] Mode 10: The first freewheeling diode is turned on, and the current flowing through the same-name terminal on the primary side of the coupling transformer is commutated from the passive auxiliary resonant circuit to the first freewheeling diode. The auxiliary resonant inductor current reversely resonates and rises, and the auxiliary resonant capacitor voltage resonates and decreases. 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-name terminal on the primary side of the coupling transformer decreases linearly. The state of the secondary side is consistent with Mode 1.

[0032] Mode 11: The current in the passive auxiliary resonant circuit is zero. At this time, the first freewheeling diode is turned on, the third and first industrial frequency power switch tubes are turned on, the first and second high frequency power switch tubes, and the fourth and second industrial frequency power switch tubes are turned off, and the circuit operates in PWM mode. The current flowing through the same-name terminal on the primary side of the coupling transformer decreases linearly, and the state of the secondary side is consistent with Mode 1.

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

[0034] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

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

[0036] 2. The topology proposed in the present invention can realize rectification within the full-wave range, further improving 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 reverse recovery problem of the freewheeling diode on the primary side of the coupling 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 very helpful for preventing interference and protecting the circuit from voltage spikes. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0039] Figure 2(a)-Figure 2(k) It is a schematic diagram of the working modes of each switch of a ZCT soft-switching DC / DC converter of the present invention when the current flows through the primary side of the coupling transformer in the forward direction;

[0040] Figure 3(a)-Figure 3(k) It is a schematic diagram of the working modes of each switch of a ZCT soft-switching DC / DC converter of the present invention, in which the current flows through the primary side of the coupling transformer in the negative direction. DETAILED DESCRIPTION

[0041] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0042] like Figure 1 As shown, the present invention proposes a ZCT soft-switching DC / DC converter, including a passive auxiliary resonant circuit connected between the upper and lower main power bridge arms, a main power bridge arm circuit with four switch tubes in series (two high-frequency power switch tubes S1 and S2 are auxiliary switch tubes to each other), a voltage and current commutation circuit (commutation bridge arm) and an isolation rectifier filter circuit. The primary side adopts a unipolar double frequency SPWM modulation method.

[0043] Input power V i The positive electrode is connected to the drain of the first high-frequency power switch tube S1 of the main power bridge arm and the fourth power frequency power switch tube Q2 of the commutation bridge arm, and is also connected to the cathode of the second freewheeling diode D2. The input power supply V i The negative electrode is connected to the source of the second high-frequency power switch tube S2 of the main power bridge arm and the third power frequency power switch tube Q1 of the commutation bridge arm, and is also connected to the anode of the first freewheeling diode D1. The source of the first high-frequency power switch tube S1 of the main power bridge arm is connected to the auxiliary resonant inductor L r One end of the main power bridge arm is connected to the cathode of the first freewheeling diode D1, and the first power frequency power switch tube Q L1 The drain of the second high-frequency power switch tube S2 of the main power bridge arm is connected to the auxiliary resonant capacitor C r One end of the main power bridge arm is connected to the anode of the second freewheeling diode D2, and the second power frequency power switch tube Q L2 The source of the auxiliary resonant inductor L r The other end is connected to the auxiliary resonant capacitor C rThe other end of the main power bridge arm, the first power frequency power switch tube Q L1 The source of the main power bridge arm is connected to the second power frequency power switch tube Q L2 The drain of the third power frequency power switch tube Q1 of the commutation bridge arm is connected to the source of the fourth power frequency power switch tube Q2 of the commutation bridge arm, and is 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 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 connected to the output capacitor C o and load resistance R o One end of the output capacitor C o and load resistance R o The other end of the coupling transformer T1 is connected to the center tap of the secondary side, and 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 first power frequency power switch tube Q of the main power bridge arm L1 And the second power frequency power switch tube Q L2 The switching frequencies of the third power switch tube Q1 and the fourth power switch tube Q2 of the commutation bridge arm are both 50Hz. The switching frequencies of the first high-frequency power switch tube S1 and the second high-frequency power switch tube S2 of the main power bridge arm are in the range of 100kHz-900kHz, and this embodiment is described at 600kHz.

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

[0046] Below Figure 1As for the main circuit structure, considering that the 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 of positive and negative current flowing through the primary side of the coupling transformer. The specific working principle and working mode of the present invention are described in conjunction with Figures 2-3.

[0047] Each working mode of the forward current flowing through the primary side of the coupling transformer (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 Figure 2(a), the second high-frequency power switch tube S2 is turned on in advance before the first high-frequency power switch tube S1 of the main power bridge arm is turned on, creating a zero current turn-on condition for the first high-frequency power switch tube S1, and the power frequency power switch tube Q1 of the commutation bridge arm and the power frequency power switch tube Q L1 Open, the commutation bridge arm power frequency power switch tube Q2, the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1 of the main power bridge arm is turned off, and the auxiliary resonant inductor current i in the passive auxiliary resonant circuit is Lr The positive direction resonates and the auxiliary capacitor voltage v Cr From the negative value resonance rise (its absolute value resonance falls), the current i flowing through the same-name terminal on the primary side of the coupling transformer T The forward linear decreases, the third freewheeling diode D3 on the secondary side is turned on, and the secondary side current flows through the output capacitor C o and load resistance R o Then return to the center tap of the coupling transformer.

[0049] Working mode 2: As shown in Figure 2(b), the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 Turn on, the auxiliary resonant inductor current i in the passive auxiliary resonant circuit Lr The resonance continues in the reverse direction, and the parasitic diode of the second high-frequency power switch tube S2 of the main power bridge arm is turned on. At this time, the voltage across the second high-frequency power switch tube S2 is clamped at zero to complete the zero voltage shutdown. The first high-frequency power switch tube S1 of the main power bridge arm, the power frequency power switch tube Q2 of the commutation bridge arm and the power frequency power switch tube Q L2 Shutdown, auxiliary capacitor voltage v Cr Dropping from the positive maximum resonance, the current i flowing through the same-name terminal on the primary side of the coupling transformer T The current transfers from the first freewheeling diode D1 to the auxiliary resonant branch, decreases linearly, and the state of the secondary side is consistent with working mode 1.

[0050] Working mode 3: As shown in Figure 2(c), when the auxiliary inductor current is equal to the current flowing through the same-name terminal of the primary side of the coupling transformer, the first high-frequency power switch tube S1 of the main power bridge arm is turned on. 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 power frequency power switch tube Q1 of the commutation bridge arm and the power frequency power switch tube Q L1 The parasitic diode of the second high-frequency power switch tube S2 of the main power bridge arm is turned on, and the power frequency power switch tube Q2 of the commutation bridge arm and the power frequency power switch tube Q L2 Turn off, the auxiliary resonant inductor current i Lr From the negative value resonance rises, the auxiliary capacitor voltage v Cr From zero resonance down, the current i flowing through the same-name terminal on the primary side of the coupling transformer T It rises linearly, and the state of the secondary side is consistent with working mode 1.

[0051] Working mode 4: As shown in Figure 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 L1 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 L2 The second freewheeling diode D2 is turned on as an auxiliary diode to assist the resonant inductor current i Lr and the auxiliary capacitor voltage v Cr The current i flowing through the same-name terminal on the primary side of the coupling transformer changes in resonance. T It rises linearly, and the state of the secondary side is consistent with working mode 1.

[0052] Working mode 5: As shown in Figure 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 L1 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 L2 The passive auxiliary resonant circuit has no current flowing through it, the second freewheeling diode D2 is turned off, and the main power circuit works in the classic PWM mode. The current i flowing through the same-name terminal on the primary side of the coupling transformer is T It rises linearly, and the state of the secondary side is consistent with working mode 1.

[0053] Working mode 6: As shown in Figure 2(f), the second high-frequency power switch tube S2 is turned on before the first high-frequency power switch tube S1 of the main power bridge arm is turned off, and the power frequency power switch tube Q1 of the commutation bridge arm and the power frequency power switch tube Q L1 Open, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube QL2 Turn off, the auxiliary resonant inductor current i Lr Rising from zero resonance, the auxiliary capacitor voltage v Cr Resonance rises, and the current i flowing through the same-name terminal on the primary side of the coupling transformer T It rises linearly, and the state of the secondary side is consistent with working mode 1.

[0054] Working mode 7: As shown in Figure 2(g), the auxiliary resonant inductor current i Lr After dropping to zero, it continues to drop in resonance, and the auxiliary capacitor voltage v Cr The parasitic diode of the second high-frequency power switch tube S2 of the main power bridge arm is turned on, and the voltage across the second high-frequency power switch tube S2 is clamped at zero, and can be turned off with zero voltage. The first high-frequency power switch tube S1 of the main power bridge arm, the power frequency power switch tube Q1 of the commutation bridge arm and the power frequency power switch tube Q L1 Open, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly, and the state of the secondary side is consistent with working mode 1.

[0055] Working mode 8: As shown in Figure 2(h), the auxiliary resonant inductor current i Lr The current i flowing through the same-name terminal on the primary side of the coupling transformer due to reverse resonance T After that, the parasitic diode of the first high-frequency power switch tube S1 of the main power bridge arm is turned on, and the first high-frequency power switch tube S1 can be turned off with zero current and zero voltage, and the power frequency power switch tube Q1 of the commutation bridge arm and the power frequency power switch tube Q L1 Open, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly, and the state of the secondary side is consistent with working mode 1.

[0056] Working mode 9: As shown in Figure 2(i), the auxiliary resonant inductor current i Lr The current i flowing through the same-name terminal on the primary side of the coupling transformer due to reverse resonance T After that, the parasitic diode of the first high-frequency power switch tube S1 of the main power bridge arm is naturally turned off, and the auxiliary resonant branch is connected with a constant current i T Power is supplied to the secondary side, and the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 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 L2The second high-frequency power switch tube S2 of the main power bridge arm is turned off, and the state of the secondary side is consistent with working mode 1.

[0057] Working mode 10: As shown in Figure 2(j), the first freewheeling diode D1 is turned on, and the current i flowing through the same-name terminal on the primary side of the coupling transformer is T The auxiliary resonant branch switches to the first freewheeling diode D1, and the auxiliary resonant inductor current i Lr Reverse resonance rises, the auxiliary capacitor voltage v Cr The resonance decreases, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 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 The second high-frequency power switch tube S2 of the main power bridge arm is turned off, and the current i flowing through the same-name terminal on the primary side of the coupling transformer T It decreases linearly, and the state of the secondary side is consistent with working mode 1.

[0058] Working mode 11: As shown in Figure 2(k), the resonant branch current is zero. At this time, the first freewheeling diode D1 is turned on, and the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 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 The second high-frequency power switch tube S2 of the main power bridge arm is turned off, and the circuit works in the classic PWM mode. The current i flowing through the same-name terminal on the primary side of the coupling transformer T It decreases linearly, and the state of the secondary side is consistent with working mode 1.

[0059] Each working mode of the negative current flowing through the primary side of the coupling 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] Working mode 1: As shown in Figure 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, and the power frequency power switch tube Q2 of the commutation bridge arm and the power frequency power switch tube Q L2 The second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The auxiliary resonant inductor current i in the passive auxiliary resonant circuit is turned off. Lr Forward resonance rises, the auxiliary capacitor voltage v CrFrom the negative value resonance rise (its absolute value resonance falls), the current i flowing through the same-name terminal on the primary side of the coupling transformer T The reverse linear decreases, the fourth freewheeling diode D4 on the secondary side is turned on, and the secondary side current flows through the output capacitor C o and load resistance R o Then return to the center tap of the coupling transformer.

[0061] Working mode 2: As shown in Figure 3(b), the resonant inductor current i Lr The resonance zero crossing causes the parasitic diode of the first high-frequency power switch tube S1 to be turned on, and the power frequency power switch tube Q2 of the commutation bridge arm and the power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T The current is transferred from the second freewheeling diode D2 to the auxiliary resonant branch, and decreases linearly in the reverse direction. The state of the secondary side is consistent with the working mode 1.

[0062] Working mode 3: As shown in Figure 3(c), the current i flowing through the same-name terminal on the primary side of the coupling transformer is T The process of switching from the second freewheeling diode D2 to the auxiliary resonant branch is completed. At this time, the second high-frequency power switch tube S2 is turned on with zero current, and the current i flowing through the same-name terminal on the primary side of the coupling transformer is T Start to commutate from the auxiliary resonant branch to the second high-frequency power switch tube S2, and commutate the power frequency power switch tube Q2 of the phase-changing bridge arm and the power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly in the reverse direction, and the state of the secondary side is consistent with working mode 1.

[0063] Working mode 4: As shown in Figure 3(d), the auxiliary resonant inductor current i Lr The zero crossing again makes the first freewheeling diode D1 conduct, and the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly in the reverse direction, and the state of the secondary side is consistent with working mode 1.

[0064] Working mode 5: As shown in Figure 3(e), the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The circuit works in the classic PWM mode, and the current i flowing through the same-name terminal on the primary side of the coupling transformer is T It rises linearly in the reverse direction, and the state of the secondary side is consistent with working mode 1.

[0065] Working mode 6: As shown in FIG3(f), the first high-frequency power switch tube S1 is turned on as an auxiliary switch tube before the second high-frequency power switch tube S2 is turned off, and the current i flowing through the same-name terminal on the primary side of the coupling transformer is T The second high-frequency power switch tube S2 starts to commutate to the auxiliary resonant branch, and the first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 Open, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly in the reverse direction, and the state of the secondary side is consistent with working mode 1.

[0066] Working mode 7: As shown in Figure 3(g), the auxiliary resonant inductor current resonates through zero, causing the parasitic diode of the first high-frequency power switch tube S1 to turn on, and it continues to resonate through the parasitic diode, and the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly in the reverse direction, and the state of the secondary side is consistent with working mode 1.

[0067] Working mode 8: As shown in Figure 3(h), the current i flowing through the same-name terminal on the primary side of the coupling transformer is T The commutation from the second high-frequency power switch tube S2 to the auxiliary resonant branch is completed, the parasitic diode of the second high-frequency power switch tube S2 is turned on, the zero voltage and zero current shutdown of the second high-frequency power switch tube S2 is completed, and the power frequency power switch tube Q2 of the commutation bridge arm and the power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T It rises linearly in the reverse direction, and the state of the secondary side is consistent with working mode 1.

[0068] Working mode 9: As shown in Figure 3(i), the auxiliary resonant branch discharges the output circuit with a constant current, and the current magnitude is equal to the current i flowing through the same terminal on the primary side of the coupling transformer. T Equal, the commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 Shutdown, the state of the secondary side is consistent with working mode 1.

[0069] Working mode 10: As shown in Figure 3(j), the current i flowing through the same-name terminal on the primary side of the coupling transformer is T The auxiliary resonant inductor current i Lr From the negative value resonance rises, the auxiliary capacitor voltage v Cr From zero resonance down, the phase change bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T The reverse linear decreases, and the state of the secondary side is consistent with working mode 1.

[0070] Working mode 11: As shown in Figure 3(k), the current i flowing through the same-name terminal on the primary side of the coupling transformer is T The commutation from the resonant branch to the second freewheeling diode D2 is completed, and the circuit works in the classic PWM mode. The commutation bridge arm power frequency power switch tube Q2 and the main power bridge arm power frequency power switch tube Q L2 The first high-frequency power switch tube S1, the second high-frequency power switch tube S2, the commutation bridge arm power frequency power switch tube Q1 and the main power bridge arm power frequency power switch tube Q L1 The current i flowing through the same-name terminal on the primary side of the coupling transformer is turned off. T The reverse linear decreases, and the state of the secondary side is consistent with working mode 1.

[0071] From the above, it can be seen that the present invention proposes a novel ZCT soft-switching DC / DC converter in which two high-frequency modulated power switch tubes in the main power bridge arm full-bridge topology serve as auxiliary switch tubes for each other. By connecting a passive auxiliary resonant circuit across the upper and lower main power bridge arms, zero-current switching of the power switch tube is achieved, thereby reducing the switching loss of the system and suppressing the influence of electromagnetic interference.

[0072] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A ZCT soft-switching DC / DC converter, characterized in that: The DC / DC converter comprises a four-switch tube series main power bridge arm circuit, a passive auxiliary resonant circuit, a voltage and current commutation circuit, an isolation rectifier filter circuit and a load resistor, wherein the four-switch tube series main power bridge arm circuit comprises two high-frequency power switch tubes that are auxiliary switch tubes to each other; the four-switch tube series main power bridge arm circuit is connected with a passive auxiliary resonant circuit above and below; The four-switch tube series main power bridge arm circuit is connected to a passive auxiliary resonant circuit and a voltage-current commutation circuit for transmission of input power supply energy; The passive auxiliary resonant circuit is used to cooperate with the working mode of the four-switch tube series main power bridge arm circuit, eliminate the switching loss of two high-frequency power switch tubes that serve as auxiliary switch tubes to each other in the four-switch tube series main power bridge arm circuit, and realize zero-current soft switching; The voltage-current phase-changing circuit is used to switch the voltage and current phases and transmit 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, thereby outputting a smooth direct current voltage.

2. The ZCT soft-switching DC / DC converter according to claim 1, characterized in that: The four-switch tube series main power bridge arm circuit comprises first to second high-frequency power switch tubes, first to second industrial frequency power switch tubes and first to second freewheeling diodes; the first and second high-frequency power switch tubes are auxiliary switch tubes to each other; The source of the first high-frequency power switch tube is connected to the drain of the first industrial frequency power switch tube, the source of the first industrial frequency power switch tube is connected to the drain of the second industrial frequency power switch tube, and the source of the second industrial frequency power switch tube is connected to the drain of the second high-frequency power switch tube; The drain of the first high-frequency power switch tube and the cathode of the second freewheeling diode are respectively connected to the positive electrode of the input voltage, and the source of the second industrial frequency power switch tube and the drain of the second high-frequency power switch tube are respectively connected to the anode of the second freewheeling diode; The source of the first high-frequency power switch tube and the drain of the first industrial frequency power switch tube are respectively connected to the cathode of the first freewheeling diode, and the source of the second high-frequency power switch tube and the anode of the first freewheeling diode are respectively connected to the negative electrode of the input voltage.

3. The ZCT soft-switching DC / DC converter according to claim 2, characterized in that: The passive auxiliary resonant circuit includes an auxiliary resonant inductor and an auxiliary resonant capacitor; one end of the auxiliary resonant inductor is connected to the cathode of the first freewheeling diode, one end of the auxiliary resonant capacitor is connected to the anode of the second freewheeling diode, and the other end of the auxiliary resonant capacitor is connected to the other end of the auxiliary resonant inductor.

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

5. The ZCT soft-switching DC / DC converter according to claim 4, 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 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; The anode of the third freewheeling diode is connected to the same-name terminal on 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 connected to one end of the output capacitor at the same time, the other end of the output capacitor is connected to the center tap on the secondary side of the coupling transformer, and the anode of the fourth freewheeling diode is connected to the other end on the secondary side of the coupling transformer; The output capacitor is connected in parallel with the load resistor, and both ends of the load resistor are connected to the positive and negative poles of the output voltage respectively.

6. The ZCT soft-switching DC / DC converter according to claim 5, characterized in that: 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 working 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 industrial frequency power switch tubes are turned on, the fourth and second industrial frequency power switch tubes and the first high-frequency power switch tube are turned off, the auxiliary resonant inductor current rises in the positive direction, the auxiliary resonant capacitor voltage rises from the negative value resonance, the current flowing through the same-name terminal on the primary side of the coupling transformer decreases linearly in the positive direction, the third freewheeling diode on the secondary side is turned on, 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; Mode 2: The third and first industrial frequency power switch tubes are turned on, the auxiliary resonant inductor current continues to resonate in the opposite direction, the parasitic diode of the second high-frequency power switch tube is turned on, and the voltage across the second high-frequency power switch tube is clamped at zero, completing the zero voltage shutdown. The fourth and second industrial frequency power switch tubes and the first high-frequency power switch tube are turned off, and the auxiliary resonant capacitor voltage drops from the positive maximum value resonance. The current flowing through the same-name end of the primary side of the coupling transformer is transferred from the first freewheeling diode to the passive auxiliary resonant circuit, and decreases linearly. The state of the secondary side is consistent with Mode 1. Mode 3: When the auxiliary resonant inductor current is equal to the current flowing through the same-name terminal on the primary side of the coupling transformer, the first high-frequency power switch tube is turned on, the third and first industrial frequency power switch tubes are turned on, the parasitic diode of the second high-frequency power switch tube is turned on, the fourth and second industrial frequency power switch tubes are turned off, the auxiliary resonant inductor current rises from negative resonance, the auxiliary resonant capacitor voltage drops from zero resonance, the current flowing through the same-name terminal on the primary side of the coupling transformer rises linearly, and the state of the secondary side is consistent with mode 1; Mode 4: The third and first industrial frequency power switch tubes and the first high frequency power switch tube are turned on, the fourth and second industrial frequency power switch tubes and the second high frequency power switch tube 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 in resonance, and the current flowing through the same-name terminal on the primary side of the coupling transformer increases linearly. The state of the secondary side is consistent with Mode 1. Mode 5: The third and first industrial frequency power switch tubes and the first high frequency power switch tube are turned on, the fourth and second industrial frequency power switch tubes and the second high frequency power switch tube are turned off, no current flows through the passive auxiliary resonant circuit, the second freewheeling diode is turned off, the main power bridge arm circuit operates in PWM mode, and the current flowing through the same-name terminal on the primary side of the coupling transformer increases linearly. The state of the secondary side is consistent with Mode 1; Mode 6: The second high-frequency power switch is turned on before the first high-frequency power switch is turned off. The third and first power-frequency power switches are turned on, and the fourth and second power-frequency power switches are turned off. The auxiliary resonant inductor current rises from zero resonance, the auxiliary resonant capacitor voltage rises from resonance, and the current flowing through the same-name terminal on the primary side of the coupling transformer rises linearly. The state of the secondary side is consistent with Mode 1. Mode 7: After the auxiliary resonant inductor current drops to zero, it continues to resonate and drop, the auxiliary resonant capacitor voltage drops from the maximum value, the parasitic diode of the second high-frequency power switch tube is turned on, 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-name terminal on the primary side of the coupling transformer increases linearly. The state of the secondary side is consistent with mode 1. Mode 8: After the auxiliary resonant inductor current reversely resonates to the current flowing through the same-name end of the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch tube is turned on, the first high-frequency power switch tube is turned off by 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-name end of the primary side of the coupling transformer rises linearly, and the state of the secondary side is consistent with mode 1; Mode 9: After the auxiliary resonant inductor current reversely resonates to the current flowing through the same-name terminal on the primary side of the coupling transformer, the parasitic diode of the first high-frequency power switch tube is naturally turned 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, and the state of the secondary side is consistent with Mode 1. Mode 10: The first freewheeling diode is turned on, and the current flowing through the same-name terminal on the primary side of the coupling transformer is commutated from the passive auxiliary resonant circuit to the first freewheeling diode. The auxiliary resonant inductor current reversely resonates and rises, and the auxiliary resonant capacitor voltage resonates and decreases. 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-name terminal on the primary side of the coupling transformer decreases linearly. The state of the secondary side is consistent with Mode 1. Mode 11: The current in the passive auxiliary resonant circuit is zero. At this time, the first freewheeling diode is turned on, the third and first industrial frequency power switch tubes are turned on, the first and second high frequency power switch tubes, and the fourth and second industrial frequency power switch tubes are turned off, and the circuit operates in PWM mode. The current flowing through the same-name terminal on the primary side of the coupling transformer decreases linearly, and the state of the secondary side is consistent with Mode 1.

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

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