CN109951085B - A Novel Full-Bridge Soft-Switching Converter with Snubber Circuit and Coupled Inductor - Google Patents

Abstract

The invention discloses a novel full-bridge full-soft switching converter with a buffer circuit and a coupling inductor. It comprises the following steps: transformer primary side full bridge inversion of the converterThe circuit consists of switching tubes S1, S2, S3 and S4. The secondary side rectification circuit of the transformer of the converter consists of diodes D1, D2, D3 and D4. Q1, Q2, D5 and C_clampConstitute a buffer circuit. C_rIs a resonant capacitor (C)_clampFar greater than C_r) L1 and L2 are coupled inductors. L is_lkAnd L_mRespectively the leakage flux and the excitation inductance of the transformer. Hypothesis C_oSufficiently large, output voltage v_oApproximately constant. Through the action of the buffer circuit, the converter can realize soft switching of all switching tubes on the primary side and rectifying diodes on the secondary side of the transformer under the condition of light load. Through the action of the coupling inductor, soft switching of all switching devices of the buffer circuit is realized. All main switching tubes on the primary side of the transformer adopt complementary symmetrical control, and the problems of duty ratio loss and circulating current are solved.

Description

A Novel Full-Bridge Soft-Switching Converter with Snubber Circuit and Coupled Inductor

technical field

The present invention relates to power electronic converter technology, especially to some soft switching converter fields.

Background technique

High-power density and high-efficiency switching converters are one of the research hotspots of high-frequency switching converters. An effective way to improve the power density of the converter is to increase the switching frequency of the converter. As the switching frequency increases, the switching losses of conventional hard-switching PWM converters increase sharply, resulting in reduced converter efficiency and limiting further improvements in power density. The converter soft switching technology can realize zero voltage switching (ZVS) or zero current switching (ZCS) of the switch tube to reduce switching loss and improve the efficiency and power density of the converter, so it has been paid more and more attention.

Phase-shifted full-bridge (PSFB) converter is a converter that realizes zero-voltage switching of primary side switches of transformers, and is widely used by researchers. However, conventional PSFB converters suffer from a series of problems, such as rectifier diode parasitic oscillation and reverse recovery, duty cycle loss and circulating current loss. At the same time, the asymmetric control method of the gate signal may lead to the DC bias phenomenon of the transformer, resulting in the additional loss and low utilization rate of the transformer, thus leading to the problem of saturation of the transformer core.

In order to solve the problems existing in the traditional PSFB converter, researchers have conducted in-depth research on it in recent years, and proposed many improvement schemes. In order to solve the problem of loss of duty cycle, a series of saturable inductors are connected to the primary side of the transformer. The inductance of the saturated inductor changes with the change of the current. Due to this characteristic of the saturable inductance, the loss of the duty cycle can be effectively reduced. Happening. However, the saturated inductor works in a bidirectional magnetization state, and the loss is relatively large. Combining the full-bridge circuit and the LLC resonant circuit through the hysteresis bridge arm broadens the soft-switching range of the traditional PSFB converter, but other problems of the traditional PSFB converter remain unsolved. The introduction of two active switches in the secondary side rectifier solves the problem of reverse recovery and realizes zero-voltage switching of all switches on the primary side of the transformer. However, at light load, the zero-voltage range is limited and the circulating current is large. Adding a diode clamp circuit on the primary side of the transformer reduces the severity of voltage spikes on the secondary side rectifier diodes, and adds additional inductance and an asymmetric pulse-width modulation (APWM) strategy to reduce switching device losses. However, the converter adds three additional inductors, adding cost, size, and weight to the circuit. Furthermore, the control strategy becomes more complex.

SUMMARY OF THE INVENTION

In order to simplify the complex control method and reduce the cost, weight and volume, the present invention proposes a novel full-bridge full-soft switching converter with a snubber circuit and a coupled inductor.

The scheme that the present invention solves the above-mentioned technical problems is:

The full-bridge inverter circuit on the primary side of the transformer of the converter is composed of switch tubes S1, S2, S3, and S4, and the rectifier circuit on the secondary side of the transformer of the converter is composed of diodes D1, D2, D3, and D4. The circuit is composed of Q1, Q2, C _clamp , D5, and then connected in parallel behind the rectifier circuit, which is the key part to realize the soft switching of the circuit. The source of the switch Q1 is connected to the common terminal of the coupled inductors L1 and L2, its drain is connected to the cathodes of the diodes D1 and D3, the capacitor C _r is connected in parallel with both ends of the switch Q1, and the capacitor C _clamp and Q2 are connected in series and then connected in parallel. The two ends of the diodes D3 and D4, wherein the other end of the capacitor C _clamp is connected to the cathode of the diode D3, and the other end of the Q2 is connected to the anode of D4. The anode of the diode is connected to the common terminal of the capacitor C _clamp and Q2, and the cathode of the diode is connected to the other end of the inductor L2. The voltage-stabilizing capacitor C _o is connected in parallel with the load end to realize the stability of the output voltage.

The technical effect of the invention is that: by adding a buffer circuit and a coupled inductance on the secondary side of the transformer, soft switching of all switching tubes of the transformer, the rectifier circuit on the secondary side and the buffer circuit can be realized. The control strategy of the primary side switch tube of the transformer is the simplest complementary symmetrical control, which avoids the loss of the duty cycle of the PSFB, the parasitic oscillation of the diode and the problems of circulating current.

Description of drawings

FIG. 1 is a schematic diagram of circuit connection of a novel full-bridge full-soft switching converter with a snubber circuit and a coupled inductor provided by the present invention.

FIG. 2 is a schematic diagram of main working waveforms provided to FIG. 1 by the present invention.

FIG. 3 is an equivalent circuit diagram of the present invention in operating mode 1. FIG.

FIG. 4 is an equivalent circuit diagram of the present invention in operating mode 2. FIG.

FIG. 5 is an equivalent circuit diagram of the present invention in operating mode 3. FIG.

FIG. 6 is an equivalent circuit diagram of the present invention in operating mode 4. FIG.

FIG. 7 is an equivalent circuit diagram of the present invention in operating mode 5. FIG.

FIG. 8 is an equivalent circuit diagram of the present invention in operating mode 6. FIG.

FIG. 9 is an equivalent circuit diagram of the present invention in operating mode 7. FIG.

FIG. 10 is an equivalent circuit diagram of the present invention in operating mode 8 .

Detailed ways

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

A novel full-bridge full-soft switching converter with snubber circuit and coupled inductor is proposed, which has a snubber circuit and coupled inductor, as shown in Figure 1. The primary side switch tube of the converter transformer is composed of S1, S2, S3 and S4. The rectifier circuit of the converter consists of diodes D1, D2, D3 and D4. The buffer circuit of the converter consists of Q1, Q2, D5 and C _clamp . C _r is a resonant capacitor (C _clamp is much larger than C _r ). L1 and L2 are coupled inductors. L _lk and L _m are the leakage and magnetizing inductances of the transformer, respectively. Assuming that C _o is large enough, the output voltage v _o is approximately constant. The reference directions of the converter voltage and current are shown in Figure 1. Each mode of the converter will be analyzed in detail as follows. In the operation mode analysis, there are 8 modes, and the working principle of the converters described in Figures 3 to 10 can be explained by the key waveforms in Figure 2.

二极管D5的电压V_D5是由于耦合电感L2作用而产生的负值。直到t1时，C_r充电完成，V_D5值为正。二极管D₅的电流在其两端的电压变为正后缓慢增加，从而实现了二极管D5的ZCS开启。Mode 1 [t0 ~ t1] (as shown in Figure 3): In this mode, the resonant capacitor C _r is charged. Before t0, power is delivered to the load through switches S1, S4, D1, D4 and Q1. At t0, Q1 is turned off, the resonant capacitor _Cr begins to charge, and resonates with the leakage inductance _Llk of the transformer and the coupled inductance L1. Since L ₁ >>L _lk , the resonant frequency of the current can be approximately calculated as

The voltage V _D5 of the diode D5 is a negative value due to the action of the coupled inductor L2. Until t1, the charging of C _r is completed, and the value of V _D5 is positive. _The current of diode D5 increases slowly after the voltage across it becomes positive, thus achieving ZCS turn-on of diode D5.

计算，随着电容C_r充电，Q2上的电压V_Q2减小，可以用以下公式表示：Mode 2 [t1~t2] (as shown in Figure 4): This is the C _clamp charging stage. This mode is similar to the previous mode. The difference is that the coupled inductors L1 and L2 participate in the resonance. The resonant frequency of the current can be approximated by

It is calculated that as the capacitor C _r is charged, the voltage V Q2 on _Q2 decreases, which can be expressed by the following formula:

是耦合电感的互感。in

is the mutual inductance of the coupled inductors.

At t2, since the voltage V _{c_clamp} of the clamping capacitor C _clamp is equal to V _rect , the value of the voltage V _Q2 reaches zero, thereby realizing the ZVS of Q2 is turned on.

Mode 3 [t2 ~ t3] (as shown in Figure 5): t2 triggers Q2. After t2, the current through diodes D1 and D4 decreases slowly. At t3, the value of i _D1 is reduced to zero, and the primary current of the converter is reduced to the excitation current of the transformer, thus realizing the ZCS turn-off of D1 and D4. Due to the conduction of Q2, the C _clamp resonates with the transformer's leakage inductor only in this mode. _{ic_clamp} in this mode can be expressed as:

Mode 4 [t3 ~ t4] (as shown in Figure 6): This is the current in the freewheeling phase of the coupled inductor. After t3, current flows through Q2 and D5. The transformer has only a small magnetizing current flowing through S1 and S4, which can be ignored. The coupled inductor current reaches zero at t4, enabling ZCS turn-off for S1 and S4 and ZCS turn-off for D5.

Mode 5 [t4 ~ t5] (as shown in Figure 7): This is the resonance stage of the resonant capacitor _Cr and the coupled inductor L1. After t4, the resonant capacitor Cr _resonates with the coupled inductor L1 and charges the coupled inductor L1 in reverse. Because C _clamp is much larger than C _r , the main series resonance is generated by the coupled inductor L1 and C _r . At t5, the V _cr of the voltage value across the capacitor C _r reaches zero, thus realizing the ZVS turn-on of Q1. At t4, the current of the coupled inductor L1 is zero, and the voltage of the resonant capacitor _Cr is:

Mode 6 [t5 to t6] (as shown in Figure 8): At t5, switches S1 and S4 are closed. After t5, the switches S1, S4 and S2, S3 resonate with the magnetizing inductor L _m , the magnetizing current i _Lm starts to charge the output capacitors of the switches S1 and S4, and discharge the output capacitors of the switches S2 and S3, the switches S2 and S3 The voltage between drops to zero. Since i _Lm flows through the body diodes of S2 and S3, the condition that the ZVS of switches S2 and S3 is turned on can be achieved. At the same time, i _Lo flows through the body diode of Q1. Until t6, the charging and discharging of the parasitic capacitance of the switch on the primary side of the transformer is completed, and the switches S2, S3, and Q1 are powered on at the same time.

Neglecting the body diode voltage of switch Q1, the voltage across coupled inductors L1 and L2 can be expressed as:

The slope of the coupled inductance decreases in the reverse direction as: k=(v _rect - v _o )/L ₁ .

Mode 7 [t6~t7] (as shown in Figure 9): This mode is the stage in which the C _clamp charges the load. Since the voltage value of the capacitor C _clamp is greater than the rectifier output voltage V _rect , the power cannot be transferred to the load immediately. Until t7, when the voltage value of C _clamp is equal to V _rect , the power can be transferred to the load.

Mode 8 [t7 to t8] (as shown in Figure 10): At t7, power is delivered to the load through diodes D2 and D3. Due to the discharge stage of C _clamp , ZCS of D2 and D3 can be turned on and ZVS of Q2 can be turned off. At t8, the discharge of the C _clamp is completed, the primary current i _pri increases to be the same as the output inductor current i _L1 , and Q2 is turned off at this time.

After Mode 8, the other half of the switching cycle begins, and the circuit operates in the same way as the first half of the switching cycle.

Claims (1)

1. The utility model provides a novel take full-bridge full soft switching converter of snubber circuit and coupling inductance which characterized in that: the transformer comprises a buffer circuit and a coupling inductance circuit, a transformer primary side full-bridge inverter circuit of the transformer consists of switching tubes S1, S2, S3 and S4, and a power supply V_inIs connected to the drain of S1, V_inThe cathode of the S-shaped diode is connected with the source electrode of the S1, the source electrode of the S1 is connected with the drain electrode of the S2, the source electrode of the S3 is connected with the drain electrode of the S4, the drain electrode of the S1 is connected with the drain electrode of the S3, and the source electrode of the S2 is connected with the source electrode of the S4; leakage inductance L_lkOne end of the source electrode is connected to S1, and the other end is connected to the same name end of the primary side of the transformer, L_mThe synonym end of the primary side of the transformer is connected to the drain of S4, the synonym end of the secondary side of the transformer is connected to the anode of D1, and the synonym end of the transformer is connected to the anode of D3; the secondary side rectification circuit of the transformer of the converter consists of diodes D1, D2, D3 and D4, wherein the anode of D1 is connected with the cathode of D2, the anode of D3 is connected with the cathode of D4, the cathode of D1 is connected with the cathode of D3, and the anode of D2 is connected with the anode of D4; the buffer circuit of the converter consists of Q1, Q2 and C_clampD5, then parallel connected behind the rectification circuit, able to realize the soft switch of transformer primary side switch tube and rectifier diode of the converter, the coupling inductor is composed of L1 and L2, able to realize the soft switch of the buffer circuit, where the source of the switch tube Q1 is connected to the synonym terminal of the coupling inductor L1, its drain is connected to the cathode common terminal of the diodes D1 and D3, the capacitor C_rA capacitor C connected in parallel with two ends of the switching tube Q1_clampOne end of the capacitor is connected with the drain electrode of Q1, C_clampThe other end is connected with the drain of a switching tube Q2, the source of Q2 is connected with the anode of D4, the anode of a diode D5 is connected with the drain of a switching tube Q2, the cathode of D5 is connected with the synonym end of an inductor L2, the synonym end of L2 is connected with the source of Q1, and a voltage stabilizing capacitor C_oConnected in parallel at the load end, and simultaneously C_oOne end is connected to the homonym end of L1, C_oThe other end is connected with the source of Q2 to keep the output voltage stable; the control strategy of the transformer primary side switch tube of the converter is simplestComplementary symmetric control is adopted, so that the problems of loss of the duty ratio of the PSFB, parasitic oscillation of a diode and circulating current are avoided;

mode 1[ t 0-t 1]: in this mode, the resonant capacitor C_rCharging, before t0, power is delivered to the load through switches S1, S4, D1, D4 and Q1, and at t0, Q1 is turned off, and the resonant capacitor C is connected with the load_rStarting charging and leakage inductance L of transformer_lkAnd the coupling inductance L1, due to L₁>>L_lkThe resonant frequency of the current can be approximately calculated as

Voltage V of diode D5_D5Is a negative value generated by the action of the coupling inductor L2, until t1, C_rCompletion of charging, V_D5The value is positive, the current of the diode D5 increases slowly after the voltage across it becomes positive, thus achieving ZCS turn-on of the diode D5;

mode 2[ t 1-t 2]: this is C_clampA charging phase, which is similar to the previous mode except that the coupling inductors L1 and L2 are involved in resonance and the resonant frequency of the current can be approximately passed

Calculation with capacitance C_rCharging, voltage V over Q2_Q2The reduction can be expressed by the following equation:

wherein

Is the mutual inductance of the coupled inductors,

at t2, because of the clamping capacitor C_clampVoltage V of_{c_clamp}Is equal to V_rectVoltage V of_Q2The value reaches zero, thereby achieving ZVS turn-on of Q2;

mode 3[ t 2-t 3]: t2 triggers Q2, after t2 the current through diodes D1 and D4 slowly drops, at t3, i_D1The value is reduced to zero, the primary current of the converter is reduced to the exciting current of the transformer, thereby realizing the ZCS turn-off of D1 and D4, and C is turned on due to the conduction of Q2_clampResonant with the leakage inductor of the transformer only in this mode, ic in this mode_clampCan be expressed as:

mode 4[ t3 to t4 ]: after t3, the current flows through Q2 and D5, the transformer only has very small exciting current flowing through S1 and S4, and the current of the coupling inductor reaches zero at t4, so that ZCS turn-off of S1 and S4 and ZCS turn-off of D5 are realized;

mode 5[ t 4-t 5]: this is the resonant capacitance C_rAnd a resonant stage of the coupling inductor L1, after t4, a resonant capacitor C_rResonates with the coupling inductor L1 and charges the coupling inductor L1 in the reverse direction because of C_clampFar greater than C_rThe main series resonance is formed by coupling inductors L1 and C_rResulting in a capacitance C at t5_rV of voltage value at two ends_crZero is reached, ZVS (zero voltage switch) of Q1 is realized, and at t4, the current of the coupling inductor L1 is zero, and the resonant capacitor C_rThe voltage of (a) is:

mode 6[ t 5-t 6]: at t5, switches S1 and S4 are closed, and after t5, switches S1, S4 and S2, S3 and excitation inductance L_mResonance occurs, exciting current i_LmStarting to charge the output capacitance of switches S1 and S4 and discharging the output capacitance of switches S2 and S3, the voltage between switches S2 and S3 drops to zero due to i_LmFlows through the body diodes of S2 and S3, and thus can reachZVS open conditions to switches S2 and S3 while i_LoThe current flows through a body diode of Q1 until t6, the charging and discharging of a parasitic capacitor of a primary side switch of the transformer are completed, and the switches S2, S3 and Q1 are electrified simultaneously;

ignoring the body diode voltage of switch Q1, the voltage of the coupled inductors L1 and L2 can be expressed as:

the slope of the coupled inductance decreases in the reverse direction as: k ═ v_rect-v_o)/L₁，

Mode 7[ t 6-t 7]: the mode is C_clampStage of charging the load, due to the capacitor C_clampIs greater than the rectifier output voltage V_rectAnd therefore power cannot be immediately delivered to the load until t7 when C_clampVoltage value of equal to V_rectThen, the electrical energy can be transferred to the load;

mode 8[ t 7-t 8]: at t7, power is transferred to the load through diodes D2 and D3 due to C_clampThe discharge phase of (1) can realize ZCS turn-on of D2 and D3 and ZVS turn-off of Q2, at t8, C_clampAfter the discharge, the primary current i_priIncrease to and output inductor current i_L1Likewise, Q2 is off at this time;

after mode 8, the other half of the switching cycle begins and the circuit operates in the same manner as the first half of the switching cycle.

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