CN100539374C - Zero-voltage switch combined full-bridge three-level direct current converter - Google Patents

Abstract

The utility model relates to a zero-voltage switching composite full-bridge three-level DC converter, which belongs to a DC converter of an electric energy conversion device. The DC converter includes a DC power supply (V _in ), a bridge circuit composed of a three-level inverter bridge arm (1) and a two-level inverter bridge arm (2), an isolation transformer (3), a resonant inductor (4) , rectification and filter circuit (6). It is characterized in that an auxiliary winding is added to the primary side of the isolation transformer, and one end of the primary winding is connected to the output end of the three-level inverter bridge arm, and the other end is connected to one end of the auxiliary winding, and two clamping diodes (D _c1 , D _c2 ) are respectively connected to the positive and negative bus bars of the DC input of the converter to form a clamp circuit (5), the other end of the auxiliary winding is connected to one end of the resonant inductor, and the other end of the resonant inductor is connected to the output end of the two-level inverter connected. This converter is suitable for wide input voltage applications, can quickly reduce the current flowing through the clamp diode, reduce losses, and improve the working environment of the clamp diode under light load conditions.

Description

Zero-Voltage Switching Composite Full-Bridge Three-Level DC Converter

1. Technical field

The zero-voltage switching composite full-bridge three-level DC converter of the invention belongs to the DC converter of an electric energy conversion device.

2. Background technology

In recent years, the application of three-level DC converters in high-voltage applications has received widespread attention, because the voltage stress of its switching tubes is only half of the input voltage. In order to improve efficiency and reduce the weight and volume of the converter, many soft-switching three-level DC converter circuit topologies have emerged in recent years. The zero-voltage switching three-level DC converter realizes the soft switching of the switching tube through the leakage inductance of the transformer and the junction capacitance of the switching tube. Zero-Voltage-Zero-Current Switching Two of the switching tubes of the three-level DC converter can realize zero-voltage switching, and the other two switching tubes can realize zero-current switching. These converters only realize the soft switching of the switching tube, but the output rectifier still has the problem of reverse recovery. The reverse recovery causes voltage oscillation, and the output rectifier has to withstand voltage spikes and is easily damaged.

Zero-voltage switching compound full-bridge three-level DC converter, the voltage stress of the switching tube of the three-level bridge arm is half of the input voltage, which can realize zero-voltage switching in a wide load range, and the high-frequency component of the output rectified waveform is small, The output filter inductance can be reduced, the input current is approximately a direct current, and the input filter can be reduced. However, there is also the problem of voltage spikes on the rectifier caused by the reverse recovery of the output rectifier.

The patent application No. 200410064935.2 "Composite full-bridge three-level DC converter and full-bridge three-level DC converter" introduces two clamping diodes into the composite full-bridge three-level DC converter, which not only maintains the original The advantages of the circuit, while effectively eliminating voltage spikes and voltage oscillations on the output rectifier.

The current in the clamping diode is the difference between the resonant inductor current and the primary current of the transformer. In order to reduce the current flowing through the clamp diode and reduce the loss, it is necessary to reduce the output filter inductance. In order to meet the requirements of the output voltage ripple, the output filter capacitor needs to be increased, thereby increasing the size and cost of the converter. At the same time, when the converter works under light load or even no-load conditions, the duty cycle is relatively small, and the clamp diode is hard turned off, which is easy to cause damage to the clamp diode.

3. Contents of the invention

The purpose of the present invention is to address the defects of the above-mentioned converters, and develop a zero-voltage switching composite full-bridge three-level DC converter with transformer auxiliary windings, which can not only eliminate voltage spikes and voltage oscillations on the output rectifier tube, but also Effectively and quickly reduce the current flowing through the clamping diode, improve the conversion efficiency, and improve the working environment of the clamping diode under light load conditions.

The zero-voltage switching composite full-bridge three-level DC converter of the present invention includes a DC power supply, a three-level inverter bridge arm, a two-level inverter bridge arm, an isolation transformer, a resonant inductor, a clamp circuit, and a rectification filter circuit , wherein the three-level inverter bridge arm includes an input voltage dividing capacitor circuit connected in parallel at the positive and negative output terminals of the DC power supply, which is formed by series connection of the first input voltage dividing capacitor and the second input voltage dividing capacitor; the first switch tube, the second switch tube, the third switching tube, and the fourth switching tube are connected in parallel to the two output terminals of the input voltage dividing capacitor circuit, and the four switching tubes are connected in parallel with a body diode and a parasitic capacitance. A flying capacitor and a freewheeling diode connected in series with the first freewheeling diode and the second freewheeling diode are connected in parallel between the series point of the first switch tube and the second switch tube and the series point of the third switch tube and the fourth switch tube. circuit, in which the series point of the two freewheeling diodes is connected to the series point of the two input voltage dividing capacitors; the two-level inverter bridge arm formed by the fifth switching tube and the sixth switching tube in series is also connected in parallel to the input voltage dividing The two output terminals of the capacitor circuit; the clamping circuit composed of two clamping diodes connected in parallel at the two ends of the three-level inverter bridge arm and the two ends of the two-level inverter bridge arm; the two same turns of the secondary side of the isolation transformer The non-identical ends of the number of secondary windings are connected in series, and the same-named end of one of the secondary windings is connected to the anode of the first rectifier diode in the rectification filter circuit, and the opposite-named end of the other secondary winding is connected to the second rectifier in the rectification filter circuit. The anode of the diode, the cathodes of the first and second rectifier diodes are connected and then connected to the positive terminal of the filter inductor, the negative terminal of the filter inductor is connected to the positive terminal of the filter capacitor, and the series point of the two secondary windings is connected to the negative terminal of the rectifier filter circuit , that is, connected to the negative terminal of the filter capacitor, characterized in that the primary winding of the isolation transformer is connected to the non-identical end of the primary auxiliary winding, the other end of the primary auxiliary winding is connected to one end of the resonant inductor, and the other end of the resonant inductor is connected to On the series connection point of the two switch tubes of the two-level inverter bridge arm, the other end of the primary winding is connected to the series connection point of the second switch tube and the third switch tube in the three-level inverter bridge arm; the clamp The series point of the two clamping diodes of the bit circuit is connected to the series point of the primary side winding of the isolation transformer and the primary side auxiliary winding.

Compared with the prior art, the main technical feature of the present invention is that the voltage oscillation and voltage spike caused by the reverse recovery of the output rectifier are eliminated due to the addition of a clamp diode circuit, and the voltage stress of the output rectifier is reduced. And the loss caused by the reverse recovery of the output rectifier is eliminated. At the same time, the auxiliary winding of the transformer is added, which can effectively and quickly reduce the current flowing through the clamp diode, and improve the working environment of the clamp diode under light load conditions.

Description of drawings

Accompanying drawing 1 is the schematic diagram of the circuit structure of the ZVS composite full-bridge three-level DC converter of the present invention.

Figure 2 is a schematic diagram of the main waveforms of the 3L working mode of the present invention.

Accompanying drawing 3 is the main waveform diagram of the 2L working mode of the present invention.

Accompanying drawing 4-19 is the equivalent circuit structural diagram of each switching mode.

Names of main symbols in the above drawings: _Vin , power supply voltage. C _d1 , C _d2 , input voltage dividing capacitor. Q ₁ -Q ₆ , switching tubes. C ₁ ~C ₆ , parasitic capacitance. D ₁ -D ₆ , body diodes. D _f1 , D _f2 , freewheeling diodes. C _ss1 , flying capacitor. L _r , resonant inductance. T _r , isolation transformer. D _c1 , D _c2 , clamping diodes. D _R1 , D _R2 , output rectifier diodes. L _f , filter inductance. C _f , filter capacitor. R _Ld , load. V _o , output voltage. v _AB , the voltage between A and B. v _rect , the rectified voltage of the secondary side of the transformer.

Detailed ways

Accompanying drawing 1 is the structural representation of the ZVS composite full-bridge three-level DC converter of the present invention with transformer auxiliary winding, and it is by three-level inverter bridge arm circuit 1, two-level inverter bridge arm circuit 2, isolation Transformer 3, resonant inductor 4, clamping circuit 5, rectification and filter circuit 6. Among them, the voltage dividing capacitors C _d1 and C _d2 have large and equal capacities, and their voltages are both half of the input voltage V _in , that is, V _cd1 = V _cd2 = V _in /2, which can be regarded as a voltage source with a voltage of V _in /2 . Four switching tubes Q ₁ -Q ₄ and their body diodes D ₁ -D ₄ and parasitic capacitors C ₁ -C ₄ , freewheeling diodes D _f1 and D _f2 , flying capacitor C _ss1 form a three-level inverter bridge arm circuit ; Switching tubes _Q5 and _Q6 , their body diodes _D5 and _D6 , and parasitic capacitors _C5 and _C6 form a two-level inverter bridge arm circuit. T _r is an isolation transformer, in addition to the primary winding n ₁ and the secondary winding n ₂ , an auxiliary winding n ₃ is added, L _r is a resonant inductance, D _c1 and D _c2 are clamping diodes, D _R1 and D _R2 Is the output rectifier diode, L _f is the output filter inductance, C _f is the output filter capacitor, R _Ld is the load.

The control method is as follows: the switch tubes _Q2 and _Q3 are 180° complementary conduction, the switch tubes _Q5 and _Q6 are 180° complementary conduction, and they are lagging behind a phase with respect to the switch tubes _Q3 and _Q2 respectively, so the definition of switch Tubes _Q2 and _Q3 are leading tubes, switching tubes _Q5 and _Q6 are lagging tubes. The switching tubes _Q1 and _Q4 are located in the same phase as the switching tubes _Q2 and _Q3 PWM work respectively, so the switching tubes _Q1 and _Q4 are defined as chopper tubes.

When the input voltage is low, the switching tubes Q ₁ and Q ₄ work in PWM, and there is a small fixed phase difference between the switching tubes Q ₂ and Q ₃ and the switching tubes Q ₆ and Q ₅ , and the switching tubes Q ₂ and Q _3. Realizing ZVS is separated from switching tubes Q ₅ and Q ₆ realizing ZVS. At this time, the output rectified voltage is a three-level waveform, which is called a three-level mode (3L mode). When the input voltage is high, the pulse width of the switching tubes _Q1 and _Q4 will be reduced to zero, and the switching tubes _Q2 , _Q3 and the switching tubes _Q6 , _Q5 work in phase shift. At this time, the output rectified voltage is The two-level waveform is called two-level mode (2L mode).

Chopper tubes Q ₁ , Q ₄ and leading tubes Q ₂ , Q ₃ realize zero-voltage switching through filter inductance and resonant inductance, and lagging tubes Q ₅ and Q ₆ realize zero-voltage switching through the energy of resonant inductance, thereby reducing the switching The switching loss of the tube improves the conversion efficiency. In the three-level inverter bridge arm circuit, freewheeling diodes D _f1 and _Df2 are also added, and the flying capacitor C _ss1 is connected between the cathode of freewheeling diode _Df1 and the anode of freewheeling diode _Df2 . The function is to connect the switching process of the two pairs of switching tubes. When the converter works in a steady state, the voltage on the flying capacitor C _ss1 is constant at V _in /2.

Below with accompanying drawing 1 main circuit structure, in conjunction with accompanying drawing 4～18 narrate concrete working principle of the present invention. It can be seen from Figure 2 that the entire converter has 20 switching modes in one switching cycle in 3L mode, which are [t ₀ before], [t ₀ , t ₁ ], [t ₁ , t ₂ ], [t ₂ , t ₃ ], [t ₃ , t ₄ ], [t ₄ , t ₅ ], [t ₅ , t ₆ ], [t ₆ , t ₇ ], [t ₇ , t ₈ ], [t ₈ , t ₉ ], [t ₉ , t ₁₀ ], [t ₁₀ , t ₁₁ ], [t ₁₁ , t ₁₂ ], [t ₁₂ , t 13 ], [t ₁₃ , t ₁₄ ], [t ₁₄ , _{t 15 ]} , [t ₁₅ , t ₁₆ ], [t ₁₆ , t ₁₇ ], [t ₁₇ , t ₁₈ ], [t ₁₈ , t ₁₉ ] (see Figure 2), where [t ₀ before, t ₉ ] is the first half cycle, [t ₉ , t ₁₉ ] is the second half cycle. The working conditions of each switch mode are analyzed in detail below.

Before the analysis, make the following assumptions: ①All switches and diodes are ideal devices, except the rectifier diodes _DR1 and _DR2 , which are equivalent to an ideal diode and a capacitor connected in parallel to simulate reverse recovery; ②All Inductors, capacitors and transformers are all ideal components; ③The flying capacitor C _ss1 is large enough, and its voltage is basically unchanged in steady state, which is V _in /2.

1. Switch mode 1 [before t ₀ ] [corresponding to Figure 4]

Before time t ₀ , the switching tubes Q ₁ , Q ₂ and Q ₆ are turned on, and the voltage between the two points AB is v _AB =V _in . The rectifier tube _DR1 on the secondary side is turned on, and the rectifier tube _DR2 is turned off. The primary side transfers energy to the secondary side.

2. Switch mode 2 [t ₀ , t ₁ ] [corresponding to accompanying drawing 5]

Turn off the switch tube Q ₁ at time t ₀ , the primary current _ip charges the capacitor C ₁ and discharges the capacitor C ₄ through the flying capacitor C _ss1 at the same time. Capacitor C ₁ and capacitor C ₄ make switch tube Q ₁ turn off approximately at zero voltage. As the voltage v _AB drops, the diode D _c2 conducts immediately, clamps the voltage v _CB to zero, the voltage v _AC drops, and the secondary side voltage drops accordingly, the voltage of the junction capacitance C _DR2 of the rectifier tube D _R2 also drops, and the junction capacitance C _DR2 is discharge. In this way, part of the output filter inductor current is discharged to the junction capacitor _CDR2 , and the rest is converted to the primary side to charge the capacitor _C1 and discharge the capacitor _C4 . Therefore, the primary side current i _p [steps down at time t ₀ , and since the potential of point C is zero, the resonant inductance bears the reverse voltage brought by the auxiliary winding, that is, the voltage on the resonant inductance is negative on the left and positive on the right, so the resonant inductance The current i _Lr has decreased, but because this period of time is very short and the voltage on the auxiliary winding is small, it can be approximately considered that its current remains unchanged. Its part above the current i _p flows through the diode D _c2 . At time _t1 , the voltage v _C1 rises to V _in /2, diode D _f1 is naturally turned on, the potential of point A drops to V _in /2, and switching mode 2 ends.

3. Switch mode 3 [t ₁ , t ₂ ] [corresponding to accompanying drawing 6]

At time t ₁ , diode D _f1 conducts, voltage v _AB is clamped at V _in /2, junction capacitance C _DR2 discharges, so current i _p steps up to I ₁ at time t ₁ , diode D _c2 turns off . At this time, if the voltage V _o >V _in ·n ₂ /2(n ₁ +n ₃ ), the current i _p will drop under the action of the voltage V _o ; at this time, if the voltage V _o <V _in ·n ₂ /2( n ₁ +n ₃ ), the current i _p rises under the action of the voltage V _in /2, and the resonant inductor current i _Lr remains equal to the current i _p . The primary side continues to transfer energy to the secondary side. Figure 6 shows the situation of voltage V _o >V _in ·n ₂ /2(n ₁ +n ₃ ).

4. Switch mode 4 [t ₂ , t ₃ ] [corresponding to accompanying drawing 7]

Turn off the switch tube Q ₂ at time t ₂ , the current _ip charges the capacitor C ₂ , and at the same time discharges the capacitor C ₃ through the flying capacitor C _ss1 . Capacitor C ₂ and capacitor C ₃ make switch Q ₂ turn off approximately at zero voltage. The voltage v _AB drops, the same as the previous switching mode 1, the diode D _c2 will be turned on, the voltage v _CB will be clamped at zero, the voltage v _AC will drop, the secondary side voltage will drop accordingly, and the voltage of the junction capacitor C _DR2 of the rectifier tube D _R2 also falls, and the junction capacitance C _DR2 is discharged. In this way, part of the output filter inductor current is discharged to the junction capacitor _CDR2 , and the rest is converted to the primary side to charge the capacitor _C2 and discharge the capacitor _C3 . Therefore, the current i _p drops step by step at t ₂ , and because the auxiliary winding voltage is small, the resonant inductor current i _Lr approximately remains unchanged, and the part higher than the current i _p flows through the diode D _c2 . At time _t3 , voltage v _C2 =V _in /2, v _C3 =0, v _AB =0.

5. Switch mode 5 [t ₃ , t ₄ ] [corresponding to accompanying drawing 8]

When the voltage v _AB =0, the diodes D ₃ and D ₄ are turned on, and at this time, the switch tubes Q ₃ and Q ₄ can be turned on with zero voltage. Diode D _c2 is still conducting, the current i _p and i _Lr are unchanged. The current in diode D _c2 is the difference between current i _p and i _Lr . At this time, the two rectifier tubes on the secondary side are turned on at the same time.

6. Switch mode 6 [t ₄ , t ₅ ] [corresponding to accompanying drawing 9]

At time t ₄ , the switch tube Q ₆ is turned off with zero voltage, and the current i _Lr charges the capacitor C ₆ and discharges the capacitor C ₅ at the same time. The voltage v _AB changes from zero to negative, and at this time the voltage v _CB =-v _C6 . The resonant inductor L _r and the capacitors C ₅ and C ₆ work in resonance. The current i _p continues to remain unchanged, and the difference between the current i _Lr and i _p flows through the diode D _c2 . At time t ₅ , the voltage v _C5 =0, the voltage v _C6 =V _in , and the diode D ₅ is naturally turned on.

7. Switch mode 7 [t ₅ , t ₆ ] [corresponding to accompanying drawing 10]

After the diode D ₅ is turned on, the switch tube Q ₅ can be turned on with zero voltage. The current i _p remains unchanged, the two rectifier tubes on the secondary side are still turned on at the same time, the voltages of the transformer primary winding, auxiliary winding and secondary winding are all zero, so the voltage V _in is all added to both ends of the resonant inductor L _r , and the resonance The inductor current i _Lr decreases linearly. At _t6 , the resonant inductor current i _Lr drops to be equal to i _p , and the diode D _c2 is naturally turned off.

8. Switch mode 8 [t ₆ , t ₇ ] [corresponding to accompanying drawing 11]

From time t ₆ , the voltage V _in is still applied to both ends of the resonant inductor, the resonant inductor current i _Lr and the current i _p drop to zero with the same slope and increase negatively, and the two rectifier tubes on the secondary side are turned on at the same time to provide the load current . At time t ₇ , the current i _p reaches the load current converted to the primary side -I _Lf (t ₇ )/K, and the switching mode ends. At this time, the rectifier tube _DR1 is turned off, and the rectifier tube _DR2 flows through the full load current .

9. Switch mode 9 [t ₇ , t ₈ ] [corresponding to accompanying drawing 12]

At time _t7 , the resonant inductance L _r and the junction capacitance C _DR1 resonate to work, that is to charge the junction capacitance C _DR1 of the rectifier tube _DR1 , and the current i _p and i _Lr continue to increase.

During this period, point A is fixed at zero potential, and the voltage v _CA of the primary winding of the transformer also rises due to the charging of junction capacitance C _DR1 , so the potential of point C has been rising. At time _t8 , the voltage of junction capacitance C _DR1 rises to 2V _in ·n ₂ /n ₁ , at this time the voltage at point C rises to V _in , diode D _c1 conducts, and clamps voltage v _CA to voltage V _in , so the junction The voltage of the capacitor C _DR1 is clamped at 2V _in ·n ₂ /n ₁ .

10. Switch mode 10[t ₈ , t ₉ ] [corresponding to accompanying drawing 13]

When the diode D _c1 is turned on, the current _ip drops stepwise to the filter inductor current converted to the primary side, and increases negatively. At this time, the voltage on the auxiliary winding is V _in ·n ₃ /n ₁ , and the voltage direction is negative on the left and positive _on the right, that is, the potential of point C is low. The right negative voltage is V _in ·n ₃ /n ₁ , so the resonant inductor current i _Lr decreases rapidly. The difference between it and the primary current _ip flows through the diode D _c1 . At _t9 , the primary current i _p and the resonant inductor current i _Lr are equal, the mode ends, and the diode D _c1 is turned off.

11. Switch mode 11 [t ₉ , t ₁₀ ] [corresponding to accompanying drawing 14]

After the diode D _c1 is turned off, the potential of point C drops gradually, the voltage v _CA drops, and the voltage v _rect decreases correspondingly after rectification on the secondary side of the transformer. When it drops to V _in n ₂ /(n ₁ +n ₃ ), the circuit enters a steady state Work, the primary side provides energy to the secondary side, the primary side current i _p is equal to the resonant inductor current i _Lr . This mode corresponds to switch mode 1.

It can be seen from Figure 3 that the entire converter has 20 switching modes in one switching cycle in 2L mode, where [t ₀ before, t ₉ ] is the first half cycle, and [t ₉ , t ₁₉ ] is the second half cycle. In the first half cycle, the working conditions of the [t ₀ before, t ₅ ] period are the same as the [t ₂ , t ₇ ] period in the 3L mode and will not be repeated here. The working conditions of the four switching modes in [t ₅ , t ₉ ] are analyzed in detail below.

1. Switch mode 1 [t ₅ , t ₆ ] [corresponding to accompanying drawing 15]

At time _t5 , the current _ip increases from zero to charge the capacitor _C4 , and at the same time discharges the capacitor _C1 through the flying capacitor _Css1 . Since the primary and secondary side voltage of the transformer is zero, the voltage v _AB is directly added to the resonant inductor L _r , so the resonant inductor L _r works in resonance with the capacitors C ₁ and C ₄ . When the voltage C _O1 =V _in /2, the diode D _f2 is turned on.

2. Switch mode 2 [t ₆ , t ₇ ] [corresponding to accompanying drawing 16]

Voltage v _AB = -V _in /2, since the primary and secondary side voltage of the transformer is still zero, so the voltage v _AB is all added to both ends of the resonant inductance L _r , and the current _ip increases linearly. At time t ₇ , the current i _p reaches the load current converted to the primary side -I _Lf (t ₇ )/K, and the switching mode ends. At this time, the rectifier tube _DR1 is turned off, and the rectifier tube _DR2 flows through the full load current .

3. Switch mode 3 [t ₇ , t ₈ ] [corresponding to accompanying drawing 17]

At time _t7 , the resonant inductor L _r and the junction capacitor C _DR1 resonate to work, that is, to charge the junction capacitor C _DR1 of the rectifier tube _DR1 , and the current i _p and the resonant inductor current i _Lr continue to increase.

During this period, point A is fixed at V _in /2 potential, and the voltage v _CA of the primary winding of the transformer also rises due to the charging of the junction capacitance C _DR1 , so the potential of point C has been rising. At time t ₈ , the voltage of junction capacitance C _DR1 rises to V _in n ₂ /n ₁ , at this time the voltage of point C rises to V _in , diode D _c1 is turned on, and the voltage v _CA is clamped to voltage V _in , so the junction The voltage of the capacitor C _DR1 is clamped at V _in ·n ₂ /n ₁ .

4. Switch mode 4 [t ₈ , t ₉ ] [corresponding to accompanying drawing 18]

When the diode D _c1 is turned on, the current _ip drops stepwise to the filter inductor current converted to the primary side, and increases negatively. At this time, the voltage on the _auxiliary winding is V _in ·n ₃ /2n ₁ , and the voltage direction is negative on the left and positive on the right, that is, the potential at point C is low. The right negative voltage is V _in ·n ₃ /2n ₁ , so the resonant inductor current i _Lr decreases rapidly. The difference between it and the primary current _ip flows through the diode D _c1 . At _t9 , the primary current i _p and the resonant inductor current i _Lr are equal, the mode ends, and the diode D _c1 is turned off.

5. Switch mode 5 [t ₉ , t ₁₀ ] [corresponding to accompanying drawing 19]

After the diode D _c1 is turned off, the potential of point C drops gradually, the voltage v _{CA drops ,} and the voltage v _rect decreases correspondingly after rectification on the _secondary side of the _transformer . State work, the primary side provides energy to the secondary side, the primary side current i _p is equal to the resonant inductor current i _Lr .

From the above analysis, it can be seen that the zero-voltage switching composite full-bridge three-level DC converter with transformer auxiliary winding can eliminate the peak voltage of the output rectifier tube well whether it is in 3L mode or 2L mode, and can effectively To quickly reduce the current flowing through the clamping diode and improve the working environment of the clamping diode under light load conditions.

It can be known from the above description that the ZVS composite full-bridge three-level DC converter with transformer auxiliary winding proposed by the present invention has the following advantages:

Due to the addition of clamping diodes, no matter in 3L mode or in 2L mode, there is no voltage oscillation and voltage spike caused by reverse recovery of the secondary side rectifier diode.

Due to the addition of the auxiliary winding of the transformer, the current flowing through the clamping diode can be effectively and quickly reduced, the loss can be reduced, and the working environment of the clamping diode can be improved at the same time under light load conditions.

The voltage stress of the switching tube of the three-level bridge arm is half of the input DC voltage, which is conducive to the selection of a suitable switching tube;

The high-frequency components in the output rectified waveform are small, which can reduce the output filter, thereby reducing the weight and volume of the filter, and improving the dynamic characteristics of the converter;

Zero voltage switching of all switching tubes can be realized in a wide load range,

The input current ripple of this converter is very small, so the input filter can be reduced.

Claims (1)

1. a Zero-voltage switch combined full-bridge three-level direct current converter comprises DC power supply (V _In), tri-level inversion brachium pontis (1), two-level inverter arm (2), isolating transformer (3), resonant inductance (4), clamp circuit (5) and current rectifying and wave filtering circuit (6), wherein tri-level inversion brachium pontis (1) comprises and is connected in parallel on DC power supply (V _In) positive-negative output end by the first input dividing potential drop electric capacity (C _D1) and the second input dividing potential drop electric capacity (C _D2) the input dividing potential drop condenser network that is connected into; By the first switching tube (Q ₁), second switch pipe (Q ₂), the 3rd switching tube (Q ₃), the 4th switching tube (Q ₄) the tri-level inversion brachium pontis (1) that is connected into successively is connected in parallel on input dividing potential drop condenser network two outputs, above-mentioned four switching tube (Q ₁, Q ₂, Q ₃, Q ₄) individual diodes in parallel separately and a parasitic capacitance, at the first switching tube (Q ₁) and second switch pipe (Q ₂) series connection point and the 3rd switching tube (Q ₃) and the 4th switching tube (Q ₄) series connection point between striding capacitance (C in parallel _Ss1) and one by the first fly-wheel diode (D _F1) and the second fly-wheel diode (D _F2) freewheeling circuit that is connected into, wherein two fly-wheel diode (D _F1, D _F2) series connection point be connected two input dividing potential drop electric capacity (C _D1, C _D2) series connection point on; By the 5th switching tube (Q ₅) and the 6th switching tube (Q ₆) the two-level inverter arm (2) that is connected into is connected in parallel on input dividing potential drop condenser network two outputs equally; By two clamping diode (D _C1, D _C2) clamp circuit (5) that is connected into is connected in parallel on tri-level inversion brachium pontis (1) two ends and two-level inverter arm (2) two ends simultaneously; Two non-same polarities with the secondary winding of the number of turn of isolating transformer (3) secondary are in series, and the end of the same name of one of them secondary winding is connected in the first rectifier diode (D in the current rectifying and wave filtering circuit (6) _R1) anode, the different name end of another secondary winding is connected in the second rectifier diode (D in the current rectifying and wave filtering circuit (6) _R2) anode, first, second two rectifier diode (D _R1, D _R2) negative electrode be connected in filter inductance (L after linking to each other _f) anode, filter inductance (L _f) negative terminal is connected in filter capacitor (C _f) anode, the series connection point of two secondary windings links to each other with the negative terminal of current rectifying and wave filtering circuit (6), promptly is connected in filter capacitor (C _f) negative terminal, it is characterized in that the former limit winding (n of described isolating transformer (3) ₁) assist winding (n with former limit ₃) non-same polarity links to each other, winding (n is assisted on former limit ₃) other end is connected in resonant inductance (4) one ends, this resonant inductance (4) other end is connected in two switching tube (Q of two-level inverter arm (2) ₅, Q ₆) series connection point on, former limit winding (n ₁) other end is connected in second switch pipe (Q in the tri-level inversion brachium pontis (1) ₂) and the 3rd switching tube (Q ₃) series connection point on; Two clamping diode (D of described clamp circuit (5) _C1, D _C2) series connection point be connected in isolating transformer (3) former limit winding (n ₁) assist winding (n with former limit ₃) series connection point.

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