WO2006024198A1

WO2006024198A1 - Snubber circuit in switching circuit with energy feedback and low-voltage turn-off

Info

Publication number: WO2006024198A1
Application number: PCT/CN2004/001018
Authority: WO
Inventors: Jie Cao
Original assignee: Jie Cao
Priority date: 2004-09-03
Filing date: 2004-09-03
Publication date: 2006-03-09

Abstract

A snubber circuit in switching circuit includes a switching element; a diode VD1, in series between the end of the switching element and the power in positive direction; a diode VD3 in parallel between the other end of the switching element and the power in reverse direction, the diode VD3 is used to conduct inverse current causing by inductor; a diode VD2 in series with a capacitor C couples to the power and the end of the switching element, to provide charging path; the snubber circuit also includes a energy feedback circuit, it includes a transformer TI, the end of primary winding of transformer is connected between the diode VD2 and capacitor C, the other end of primary winding of transformer is connected between the end of the switching element and diode VD1; the input of bridge rectifier VD4-7 couples to the secondary winding of transformer in parallel and the output couples to power in parallel.

Description

Switch snubber circuit with energy feedback and low voltage shutdown

The present invention relates to a switch snubber circuit and, more particularly, to a switch snubber circuit having energy feedback and low voltage turn-off.

Background technique

For any circuit with a switch, when the current flowing through the switch is turned off at a certain moment, the distributed inductance (L _s ) existing in the circuit and the inductance in the load (the stored energy of the LJ will be simultaneously released. According to the inductance The principle of non-mutation can not be mutated. The release of energy when the switch is turned off is carried out in such a way that the voltage suddenly increases, and its energy is W _L =LV / 2. The current and voltage waveforms on the switch are shown in Figure 1. Figure la is the switch circuit diagram It can be seen from Figure lb that when Q is turned off from the on state, high dv/dt and overvoltage are generated at both ends of the switch, when L (the sum of L _s and L _L ) and I in the circuit The larger the overvoltage, the higher the overvoltage generated. This is the reason why the overvoltage breakdown of the air occurs when the air switch is turned off in the power system we often see. When the switching circuit composed of solid devices operates at high frequency, Not only will the overvoltage as described above be generated, but also a certain turn-off loss on the switch. The loss is P _Q =LI ² f /2, and the higher the frequency f, the greater the loss. If this is not the overvoltage and loss Limit, dv/dt, P _Q and overvoltage are outside the rating of the switching device and the switching device is damaged.

Sheng Zuquan and Zhang Li proposed in the 2000 IGBT module application technology seminar, "IGBT module drive and protection technology" published in May 2000, in order to make the overvoltage of IGBT turn off more effective suppression and reduction For the turn-off loss of small I GBT, it is usually necessary to set the shutdown buffer absorption circuit for the IGBT main circuit.

Figure 2 shows a prior art charge and discharge type I GBT buffer absorption circuit. The RCD absorption circuit is directly connected in parallel across the collector and emitter of the IGBT. When I GBT is turned off, the voltage of the snubber capacitor C _s rises from zero, which makes the current and voltage trajectory of the IGBT turn off close to the current and voltage coordinate axes, which improves the safety of the IGBT when it is turned off, and reduces its Switching loss. However, since the resistor R _s needs to withstand the current of charging and discharging the capacitor C _s from zero voltage, the power consumption thereof is large, and when the operating efficiency is high, the operating efficiency of the device is seriously affected. Summary of the invention

In order to solve the above problems in the prior art, the technical problem to be solved by the present invention is to provide a switch snubber circuit capable of absorbing energy during a switch-off process and returning energy during switching to a power source.

The present invention provides a switch snubber circuit for use in a switching circuit. The snubber circuit includes a switching element; a first diode (v _D1 ) is forwardly connected in series between one end of the switching element and a power supply; a third diode (V _D3 ) is anti-parallel in the Between the other end of the switching element and the power supply, a path is provided for the inductive reverse current in the circuit; a second diode (V _D2 ) and a capacitor (C) connected in series therewith are connected in parallel at the other end of the switching element Between the power sources, a charging path is formed; the switch buffer circuit further includes: an inverter transformer (TI) having one end of the primary winding connected to the second diode (V _D2 ) and the capacitor (C) Between the other end is connected between the switching element and the first diode; a rectifier bridge (V _D4 _ ₇ ) whose pair of inputs are connected in parallel on the secondary winding of the inverter transformer (TI) , a pair of outputs are connected in parallel to the power supply. When the switching element is turned off, the current in the loop is charged to the capacitor (C) through the second diode (V _D2 ), which reduces the dv/dt turn-off; when the switching element is turned on, the charge stored in the capacitor (C) After passing through the primary winding of the inverter transformer (TI) and the first diode (V _D1 ), then flowing through the switching element, and the discharge current is transformed by the transformer (TI) impedance, after the rectifier bridge (V _D4 _ ₇ ) After rectification, the electric field energy on the capacitor (C) is fed back to the DC power source.

The above switching element may be a mechanical electromagnetic switch.

Further, the above switching element may be a semiconductor solid state switch.

Furthermore, the above switching element may be an IGBT.

With the switch buffer structure of the present invention, when the switching element is turned off, the current in the loop charges the capacitor, thereby absorbing the energy during the turn-off process, thereby achieving a low voltage turn-off on the switch; when the switching element is turned on, the capacitor After the primary line of the inverter transformer is discharged, the discharge current is transformed by the transformer impedance and rectified by the rectifier bridge, and the electric field energy on the capacitor is fed back to the DC power source. This can significantly improve the operating state of the switch, eliminate the loss and electrical stress during turn-off, extend the life of the switch, and improve reliability. And for high-power high-frequency switching circuits, energy feedback is achieved, making the circuit The conversion efficiency is significantly improved.

DRAWINGS

1 is a schematic diagram of current and voltage waveforms on a switch of the prior art;

2 is a prior art charge and discharge type IBGT buffer absorption circuit;

Figure 3 is a switch buffer circuit in accordance with a first embodiment of the present invention;

4 is a schematic diagram showing current and voltage waveforms on a switch and a capacitor when a switch is turned off in a switch snubber circuit according to a first embodiment of the present invention;

Figure 5 is a switch snubber circuit in accordance with a second embodiment of the present invention.

detailed description

Referring to Figure 3, the circuit in the dashed line is an embodiment of the present invention. Wherein V is a switching element, a first diode (V _D1 ) is forwardly connected in series between one end of the switching element V and a power supply; a diode V _{D2 is} connected in series with the capacitor C in parallel with the switching element Between the other end and the power source, a third diode (V _{D 3} ) is connected in anti-parallel between the other end of the switching element and the power supply to provide a path for the inductive reverse current in the circuit; A diode (V _D2 ) and a capacitor ( C ) connected in series therewith are connected in parallel between the other end of the switching element and a power source to form a charging path; the switching buffer circuit further includes: an inverter transformer (TI) One end of its primary coil is connected between the second diode (V _D2 ) and the capacitor (C), and the other end is connected between the switching element and the first diode; a rectifier bridge (V _D4 _ ₇ ), its pair of inputs are connected in parallel on the secondary winding of the inverter transformer (TI), and a pair of outputs are connected in parallel to the power supply. . ₂ In addition to providing a charging path for the capacitor C and preventing the discharge current from flowing directly through the switching element V when the capacitor C is discharged, the blocking capacitor C is directly connected to the inductor l existing in the load and the distributed inductance L _s in the circuit to prevent The current oscillation is formed; the main function of the diode V _{D 1} connected in series with the V-terminal of the switching element is to directly block the capacitor C, the direct connection between the inverter transformer TI and the inductors LL, L _S to prevent oscillation from forming. The freewheeling diode V _{D3 is} connected in anti-parallel across the switching element V to provide a path for the inductive reverse current in the circuit. The capacitance C of the inverter transformer TI stored energy through rectifier bridge v _D4 is turned on when the V - u _d return ends ₇ after rectification.

When the switch V is turned on, the current flows through the switch through v _D1 , and the voltage across the V is the conduction saturation voltage drop (I GBT device switch is generally 2V - 3V), at this time, the power on the capacitor C The pressure U _c is also the value. When the switch V is at t. When the time starts to turn off, the original current cannot be abruptly changed due to the presence of the distributed inductance L _s in the loop, and it charges C in a constant current manner, and u _c gradually rises. It is well known that any type of switch has a speed during switching, and its speed is different for different switching components. Mechanical electromagnetic switches are typically in the millisecond range, while IGBT semiconductor solid state switches are in the microsecond range. So it takes time when the current i changes from V to C, at t. - During this time, the current in V is decreasing, the current in C is rising, the sum of these two currents is equal to i, and the conversion of current V to C is completed, so t. - Turn off time for V. The current and voltage waveforms on V and C during shutdown are shown in Figure 4.

It can be seen from the waveform diagram of Fig. 4 that due to the presence of the capacitor C, the switch V is turned off until the moment is completely turned off, the voltage of the switch V is always the saturation voltage at the time of conduction, and the voltage is very low, thereby achieving near-low voltage. Zero voltage is turned off. Therefore, the turn-off loss on the switch is extremely small. At t ₂ , the charging of capacitor C ends and the circuit is in a steady state. At this time, the electric field energy stored by the capacitor C is CU _c ² /2.

When the switch V is turned on, the load current I flows through V, and the charge stored by the capacitor C passes through the primary of the inverter transformer 1\ to form the discharge current i _e also through the switch V. When the discharge current of the capacitor C passes through the inverter transformer, the secondary current after the impedance transformation is rectified by V _D4 _ ₇ , and all the electric field energy on the C is fed back to the DC bus. This completes a process of shutting down and opening. Repeat the above process later.

The switch snubber circuit shown in Figure 5 is another embodiment of the present invention. V _D2 provides a charging path for C and prevents direct flow through V during discharge. The freewheeling diode V _D3 provides a path for the inductive reverse current in the circuit. The inverter transformer TI returns the energy stored in C to the DC bus after rectification by the rectifier bridge V _D4 _ ₇ when V is turned on. The working principle of this embodiment is the same as that of the previous embodiment.

Although the invention has been described in detail by way of examples, the invention is not limited to the embodiments described above. It will be understood by those skilled in the art that various modifications and improvements can be made to the present invention without departing from the spirit of the invention.

Claims

Rights request

A switching buffer circuit for use in a switching circuit; the buffer circuit includes a switching element; a first diode (V _D1 ) is forwardly connected in series between one end of the switching element and a power supply; A triple diode (V _D3 ) is connected in anti-parallel between the other end of the switching element and the power supply to provide a path for inductive reverse current in the circuit; a second diode (V _D2 ) and a capacitor connected in series therewith (C) is connected in parallel between the other end of the switching element and the power source to form a charging path; and characterized in that it further comprises an energy return circuit; the energy return circuit comprises: an inverter transformer (TI), which One end of the primary coil is connected between the second diode (V _D2 ) and the capacitor (C ), and the other end is connected between the switching element and the first diode; a rectifier bridge ( V _D4 _ ₇ ) , whose pair of inputs are connected in parallel on the secondary winding of the inverter transformer (TI), and a pair of outputs are connected in parallel to the power supply.

2. The switching buffer circuit of claim 1 wherein the switching element is a mechanical electromagnetic switch.

3. The switching buffer circuit of claim 1 wherein the switching element is a semiconductor solid state switch.

4. The switching buffer circuit according to claim 3, wherein the switching element is IGBT ₀