CN104935173B - A kind of current source type full bridge PWM converter with auxiliary converter circuit - Google Patents

Abstract

The invention relates to a current source type full-bridge PWM converter with an auxiliary commutation circuit, which includes an inverter circuit, a resonant network, a transformer, a rectification filter network, and two auxiliary branches, each of which is composed of an auxiliary Transformer, auxiliary switching tube and capacitor, the primary side of two auxiliary transformers is connected in series with the emitters of the two lagging bridge arms, and the secondary side of the two auxiliary transformers is connected in parallel with switching tube and capacitor; it controls the turn-off and conduction of the two auxiliary switching tubes , to cooperate with the commutation between the four main switching tubes. The invention effectively solves the two main problems in the traditional current source type full-bridge PWM converter by adding two auxiliary branches respectively on the lagging bridge arm of the traditional current source type PWM converter and matching with appropriate driving pulses. The big problem, namely the commutation of the lagging arm and the loss of duty cycle, improves the working efficiency of the converter.

Description

A Current Source Full Bridge PWM Converter with Auxiliary Commutation Circuit

technical field

The invention relates to the field of electricity, in particular to a technology for reducing switching loss of power devices, in particular to a current source type full-bridge PWM converter with an auxiliary commutation circuit.

Background technique

Full-bridge PWM (Pulse Width Modulation) converters have been widely used in high-power DC-DC (direct-current-direct current) power conversion. However, its lifespan and efficiency are two aspects that we need to focus on. The voltage source phase-shifted full-bridge converter operating in the ZVS (Zero Voltage Switching) state is one of the most widely used circuit topologies today. Its advantages lie in its simple structure and good working performance. However, in its circuit topology In the DC side, a large-capacity electrolytic capacitor is connected in parallel, so that the DC side voltage is basically pulsating, and the capacitor also plays a role in buffering reactive energy. However, the working life of the electrolytic capacitor is usually about 10,000 hours, which is much lower than The expected working life of the converter has thus become a bottleneck restricting the further improvement of the converter's life. However, in the circuit topology of the current source type full-bridge PWM converter, unlike the voltage source type, its DC side is connected in series with a large inductance, so that the DC side current is basically pulsating, and the large inductance also plays a role in buffering reactive energy. Because the use of electrolytic capacitors is avoided, the working life of the converter is prolonged; on the other hand, in order to maximize the power density of the converter, reducing power loss and increasing switching frequency are the two main design directions. However, increasing the switching frequency will inevitably increase the switching loss of the device, so we need to reduce the switching loss of the device through soft switching. The voltage source phase-shifted full-bridge converter operating in the ZVS state is one of the most widely used soft-switching topologies today, but ZVS is more suitable for switching devices such as MOSFETs (Metal-Oxide-Semiconductor FETs). In the case of high voltage and high power, IGBT (Insulated-Gate Bipolar Transistor) has been widely used because of its strong current-carrying capacity and low conduction loss. However, due to the tail current when it is turned off, it will cause its There are high turn-off losses during turn-off. Therefore, in the case of high voltage and high power, the current-source full-bridge PWM converter operating in the ZCS (Zero Current Switching) state is more conducive to improving the efficiency of the converter than the voltage-source full-bridge circuit operating in the ZVS state. In addition, the output terminal of the current source type full-bridge PWM converter does not need to connect a huge output filter inductor, which avoids the high-frequency oscillation of the rectifier diode and the resonant inductor, and reduces the problem of high voltage stress of the diode, which also makes the current source type Compared with the voltage source type, the converter is more suitable for high voltage and high power applications.

Due to the difficulty of commutation in the lagging bridge arm of the traditional current source full-bridge PWM converter, the selection of the resonant capacitor and resonant inductance in the circuit must meet the needs of the circuit commutation, resulting in a loss of duty cycle , the conduction loss is too large, the current and voltage stress is too large and other problems also seriously affect the efficiency of the traditional current source full-bridge PWM converter; in addition, due to the limitation of the switching tube commutation mode, the traditional current source full bridge The control of the input current by the PWM converter is very limited, which also causes many problems in practical applications.

Qian Sun of Sichuan University proposed a current-source full-bridge PWM converter with controllable energy of the resonant capacitor determined by the magnitude of the input current. As shown in Figure 1, the converter is based on the circuit topology of the traditional current-source converter The auxiliary network 100 is connected in series on the primary side of the transformer, and the auxiliary network consists of two auxiliary switching tubes S₁, S₂and resonant capacitorC _rParallel connection, the characteristic of this circuit topology is that the energy in the resonant capacitor is different under different current input conditions, so that the resonant energy in the circuit loop is different according to the working conditions. On the one hand, it realizes the ZCS of the main switching tube, and on the other hand On the one hand, the high device conduction loss caused by excessive resonance energy is reduced, and in addition, the working range realized by the converter ZCS can be expanded. However, due to the charging and discharging process of its resonant capacitor, the circuit topology still has an obvious duty cycle loss problem, so that the efficiency of the converter cannot be further improved.

Contents of the invention

The present invention aims at the problems existing in the traditional current source type full-bridge PWM converter, and proposes a current source type full-bridge PWM converter with an auxiliary commutation circuit, which effectively solves the main problems in the traditional current source type full-bridge PWM converter. The commutation of the lagging bridge arm and the loss of the duty ratio exist, and the working efficiency of the converter is improved.

The technical solution of the present invention is: a current source full-bridge PWM converter with an auxiliary commutation circuit, including an inverter circuit, a resonant network, a transformer, and a rectification and filtering network.V _in, input inductanceL _inand four main switches Q₁, Q₂, Q₃, Q₄The current source type full-bridge inverter circuit structure is composed of the main switching tube Q₁and Q₃Constitute the advanced bridge arm, the main switch tube Q₂and Q₄It constitutes the lagging bridge arm, and also includes two auxiliary branches, the first auxiliary branch is formed by the auxiliary transformer T₁, Auxiliary switch tube S₁and capacitanceC ₁constitute, the auxiliary transformer T₁The primary side is connected in series with the lagging bridge arm Q₂emitter, the auxiliary transformer T₁Secondary side parallel switch tube S₁and capacitanceC ₁; The second auxiliary branch is provided by the auxiliary transformer T₂, Auxiliary switch tube S₂and capacitanceC ₂constitute, the auxiliary transformer T₂The primary side is connected in series with the lagging bridge arm Q₄emitter, the auxiliary transformer T₂Secondary side parallel switch tube S₂and capacitanceC ₂; Control switch tube S₁and S₂The turn-off and conduction of the four main switch tubes Q₁, Q₂, Q₃, Q₄exchange between.

The capacitor in the auxiliary branchC ₁withC ₂Both are film capacitors, the auxiliary switch tube S₁and S₂Both are insulated gate bipolar transistors IGBT, auxiliary switch tube S₁In the main switch Q₂Open before opening, the auxiliary switch tube S₂In the main switch Q₄Open before opening.

The resonant network consists of a resonant inductor, a resonant capacitor, a capacitorC ₁and capacitanceC ₂Composition; resonant inductance including external resonant inductanceL _rand the leakage inductance of the transformer T itself; the resonant capacitor except the resonant capacitorC _rAlso includes the output rectifier diode D₁、D₂、D₃、D₄Its own junction capacitance and the distributed capacitance between the windings of the transformer T itself; capacitanceC _r,C ₁withC ₂Both are film capacitors.

The rectification and filtering network is a full-bridge rectification and filtering structure composed of four diodes D ₁ , D ₂ , D ₃ , D ₄ and one output capacitor C.

The beneficial effect of the present invention is that: the current source type full-bridge PWM converter of the baseband auxiliary commutation circuit of the present invention, by respectively adding two auxiliary branches on the hysteresis bridge arm of the traditional current source type PWM converter, cooperates with appropriate In the case of driving pulses, it effectively solves the two main problems in the traditional current source full-bridge PWM converter, that is, the commutation of the lagging bridge arm and the loss of duty cycle, and improves the working efficiency of the converter.

Description of drawings

Figure 1 is a circuit diagram of a soft switching circuit with variable resonance energy based on a current source full-bridge PWM converter;

Fig. 2 is the circuit diagram of the current source type full-bridge PWM converter with auxiliary commutation circuit of the present invention;

3 to 7 are working process diagrams of the current source full-bridge PWM converter with auxiliary commutation circuit in each period of the present invention;

Fig. 8 is a circuit working waveform diagram of the embodiment of the present invention.

detailed description

The embodiments of the present invention add auxiliary branches 200 and 201 to the lagging bridge arm respectively on the circuit topology of the traditional current source full-bridge PWM converter, thereby facilitating the completion of the commutation of the lagging bridge arm and reducing the original occupation. The empty ratio is lost, thereby improving the working efficiency of the converter; at the same time, the circuit topology and working process are simple and easy to implement.

As shown in Fig. 2, the current source type full-bridge PWM converter circuit with auxiliary commutation circuit of the present invention includes an inverter circuit, a resonant network, an auxiliary branch, a transformer and a rectification filter network.

The inverter circuit adopts the power supplyV _in, input inductanceL _inand four main switches Q₁, Q₂, Q₃, Q₄The structure of the current source type full-bridge inverter circuit, the switch tube Q₁, Q₂, Q₃, Q₄Both are insulated gate bipolar transistors IGBT, Q₁and Q₃Constitutes the leading bridge arm, Q₂and Q₄The lagging bridge arm is formed, and the four-way control signal with fixed frequency drives the switch tube to conduct, leading the leading bridge arm Q₁and Q₃The driving pulse is complementary, the lagging arm Q₂and Q₃The driving pulses of the lagging bridge arm are complementary, the driving pulse of the lagging bridge arm lags behind the driving pulse of the leading bridge arm for a certain period of time, and the duty cycle of the driving pulses is greater than 50%, thus completing the working condition of the current source full-bridge inverter circuit; The resonant network is composed of resonant inductor, resonant capacitor, capacitorC ₁and capacitanceC ₂Composition; resonant inductance includes external resonant inductanceL _rand the leakage inductance of the transformer T itself; the resonant capacitor except the resonant capacitorC _rAlso includes the output rectifier diode D₁、D₂、D₃、D₄The junction capacitance of itself and the distributed capacitance between the windings of the transformer T itself; the auxiliary branch includes the auxiliary branch 200 and the auxiliary branch 201, wherein the auxiliary branch 200 is composed of the transformer T₁, auxiliary switch tube S₁and capacitanceC ₁form, the transformer T₁The primary side is connected in series to the lagging bridge arm Q₂the emitter of the transformer T₁Secondary side parallel switch tube S₁and capacitanceC ₁; Auxiliary branch 201 by transformer T₂, auxiliary switch tube S₂and capacitanceC ₂form, the transformer T₂The primary side is connected in series to the lagging bridge arm Q₄the emitter of the transformer T₂Secondary side parallel switch tube S₂and capacitanceC ₂;Transformer T₁and T₂It is composed of magnetic core, primary winding and secondary winding. The magnetic core material is made of soft ferrite, and the primary and secondary windings are made of enameled wire; the capacitorC ₁withC ₂Both are film capacitors, the auxiliary switch tube S₁and S₂Both are insulated gate bipolar transistors IGBT; the transformer T is composed of a magnetic core, a primary winding and a secondary winding. The side winding is made of enameled wire and connected to the rectification and filtering circuit; the rectification and filtering network is composed of 4 diodes D₁、D₂、D₃、D₄and an output capacitorC A full-bridge rectification and filtering structure is formed. The input of the rectification and filtering network is connected to the secondary side of the transformer T, and the output is connected to the output load.R .

Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7 are the working process of the current source full-bridge PWM converter with auxiliary commutation circuit in half a cycle, and Figure 8 is the working process of the current source full-bridge PWM converter Working waveform diagram of auxiliary commutation circuit:

existt ₀Referring to Figure 3 before the moment, the switching tube Q in the primary side circuit of the transformer T₁and Q₄conduction, the auxiliary switch S₁is off, the auxiliary switch S₂In conduction, the rectifier diode D in the secondary circuit₂and D₃Conduction, the energy is transmitted to the secondary side;

[t ₀,t ₁] Referring to Figure 4,t ₀Time switch tube Q₃Turn on, start the commutation process of the leading bridge arm, during this period, the switching tube Q in the primary side circuit of the transformer T₁, Q₃and Q₄conduction commutation, auxiliary switching tube S₁maintained off, the auxiliary switch S₂Maintain conduction; the rectifier diode D in the secondary circuit₂and D₃conduction. Flow through the switch tube Q₁The current to the switch tube Q₃Commutation, so that the switching tube Q₁Shut down under ZCS conditions, during which energy is still transferred to the secondary side.

[t ₁,t ₂] Referring to Figure 5,t ₁Time switch tube Q₁and auxiliary switch S₂During this period, the switch tube Q in the primary side circuit of the transformer T₃and Q₄The freewheeling current is turned on, the voltage on the primary side of the transformer is zero, and it flows through the switch tube Q₃and Q₄The current through the transformer T₂To the capacitanceC ₂Charging, auxiliary switch tube S₁Open; four rectifier diodes D in the secondary circuit₁、D₂、D₃and D₄Both conduct freewheeling, the voltage on the secondary side of the transformer is zero, and the output capacitor voltage maintains the output voltage.

[t ₂,t ₃] Referring to Figure 6,t ₂Time switch tube Q₂Turn on, start the commutation process of the lagging bridge arm, during this period, the switching tube Q in the primary side circuit of the transformer T₂, Q₃and Q₄conduction commutation, auxiliary switching tube S₁To maintain conduction, the auxiliary switch S₂Keep off; the rectifier diode D in the secondary circuit₁and D₄conduction. Capacitance in auxiliary branchC ₂Under the action of the current completed by the switching tube Q₄to Q₂The commutation process makes the switching tube Q₄In turn-off under ZCS condition, the resonant inductanceL _rcurrent reverse, resonant capacitorC _rvoltage reverse;

[t ₃,t ₄] Referring to Figure 7,t ₃Time switch tube Q₄During this period, the switch tube Q in the primary side circuit of the transformer T₂and Q₃conduction, the auxiliary switch S₁To maintain conduction, the auxiliary switch S₂Keep off; the rectifier diode D in the secondary circuit₁and D₄Turned on, the energy is transmitted to the secondary side. At this point, the working process of the first half cycle of the circuit is over, and the working process of the second half cycle of the circuit is started. Since the working process of the second half cycle of the circuit is similar to that of the first half cycle, the working process of the second half cycle of the circuit will not be repeated here; And the auxiliary switch tube S₁In the switching tube Q₃When it is turned off, it can be turned off, and the auxiliary switch tube S₂In the switching tube Q₄Just turn it off before turning it on.

Figure 8 is the working waveform diagram of the current source full-bridge PWM converter with auxiliary commutation circuit, from top to bottom is the switching tube Q₁The driving waveform of the switch tube Q₂The driving waveform of the switch tube Q₃The driving waveform of the switch tube Q₄The driving waveform of the auxiliary switch tube S₁The driving waveform of the auxiliary switch tube S₂Drive waveform, resonant inductanceL _rThe current waveform of the auxiliary switch tube S₂The collector current waveform, capacitanceC ₂current waveform, resonant capacitorC _rThe voltage waveform, capacitanceC ₂Voltage waveform at both ends, switching tube Q₃Collector current waveform, switching tube Q₄Collector current waveform, switching tube Q₃The voltage waveform at both ends of the collector and the emitter and the switching tube Q₄The voltage waveforms across the collector and emitter terminals.

Transformer T in the auxiliary branch circuit designed by the present invention₁and T₂The turn ratio of the primary and secondary sides can be adjusted to a certain extent according to the needs and actual conditions so that the auxiliary branch can work better in different situations, that is, by adjusting the transformer T₁and T₂On the one hand, the turns ratio meets the capacitance in the auxiliary branchC ₁orC ₂Charging requirements, in order to achieve the effect of lagging bridge arm auxiliary commutation, on the one hand, improve the auxiliary switch tube S in the auxiliary branch as much as possible₁and S₂The current and voltage value when turning on and off, so as to reduce the auxiliary switch tube S under the premise of satisfying the commutation₁and S₂loss.

In the design of the present invention, due to the addition of auxiliary branches in the lagging bridge arm, the rear bridge arm Q₂and Q₃When the commutation is turned on, due to the capacitor in the auxiliary branchC ₁withC ₂The existence of the lagging bridge arm makes it easy to commutate and effectively reduces the resonant capacitanceC _rThe size of the value solves the original serious duty cycle loss problem and improves the working efficiency of the converter. At the same time, due to the simple topology of the circuit, the parameters in the circuit have certain flexibility, which is easy to control and realize.

Claims (4)

1. A current source type full-bridge PWM converter with an auxiliary commutation circuit, comprising an inverter circuit, a resonant network, a transformer, a rectification filter network, and the inverter circuit adopts a power supply V _in , an input inductance L _in and four main Current source full-bridge inverter circuit structure composed of switching tubes Q ₁ , Q ₂ , Q ₃ , and Q ₄ , in which the main switching tubes Q ₁ and Q ₃ form the leading bridge arm, and the main switching tubes Q ₂ and Q ₄ form the lagging bridge The arm is characterized in that it also includes two auxiliary branches. The _first auxiliary branch is composed of an auxiliary transformer T1, _an auxiliary switch tube S1 and a capacitor _C1 . _The primary side of the auxiliary transformer T1 is connected in series with the lagging bridge arm _Q2 . _The emitter, the secondary side of the auxiliary transformer T1 is connected in parallel with the switching tube S1 and the capacitor _{C1 ;} the _second auxiliary branch is composed _of the auxiliary transformer _T2 , the auxiliary switching tube S2 and the capacitor _C2 , and the primary side of the auxiliary transformer T2 is connected in series with the lagging The emitter of the bridge arm Q ₄ , the secondary side of the auxiliary transformer T ₂ is connected in parallel with the switching tube S ₂ and the capacitor C ₂ ; it controls the switching off and on of the switching tubes S ₁ and S ₂ , and cooperates with the four main switching tubes Q ₁ , Q ₂ , The commutation between Q ₃ and Q ₄ . 2. a kind of current source type full-bridge PWM converter with auxiliary commutation circuit according to claim 1, it is characterized in that, in described auxiliary branch, electric capacity C ₁ and C ₂ are thin-film capacitors, auxiliary switching tube Both S ₁ and S ₂ are insulated gate bipolar transistors IGBT, the auxiliary switch S ₁ is turned on before the main switch Q ₂ is turned on, and the auxiliary switch S ₂ is turned on before the main switch Q ₄ is turned on. 3. a kind of current source type full-bridge PWM converter with auxiliary commutation circuit according to claim 2, is characterized in that, described resonant network is made of resonant inductance, resonant capacitor, electric capacity C ₁ and electric capacity C ₂ ; The resonant inductance includes the external resonant inductance L _r and the leakage inductance of the transformer itself; the resonant capacitor includes the output rectifier diodes D ₁ , D ₂ , D ₃ , and D ₄ in addition to the external resonant capacitor C _r , and the junction capacitance between the transformer's own windings. The distributed capacitance; capacitance C _r , C ₁ and C ₂ are film capacitance. 4. A kind of current source type full-bridge PWM converter with auxiliary commutation circuit according to claim 3, it is characterized in that, described rectification filtering network is made up of 4 diodes D ₁ , D ₂ , D ₃ , D A full-bridge rectifier filter structure composed of ₄ and 1 output capacitor C.