JPH0378432A - Protective circuit for transistor bridge - Google Patents

Abstract

PURPOSE:To manufacture a simple protective circuit preventing the rupture of a module element by inserting high-speed fuses to each transistor on the positive pole side in a bridge composed of module type transistors. CONSTITUTION:In an inverter bridge consisting of IGBTs(Insulated Gate Bipolar Transistor), the positive pole side of a DC bus is connected to the collectors of the IGBTs 71-1-71-n through fuses 31-1-31-n. Bypass capacitors 8-1-8-n are further connected. Since fault currents are reduced when parallel elements are increased on complicate trouble such as the case of the short circuit of one IGBT 72-1, the emitter of the IGBT 72-1 is melted before the fuse is blown. When the emitter starts its melting, collector potential is output to a gate, another IGBT connected in parallel is turned ON and fault currents are increased, and fuses 31-1-31-n and 32 are melted, thus preventing the rupture of the IGBT.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a protection circuit for a transistor bridge in which a plurality of module type transistors and elements are connected in parallel. For example, in a voltage source inverter, bipolar transistors, MOS FETs,
IGBT (Insulated Gate Bipol)
arTransistor), etc., and bipolar transistors are mainly used for inverter capacities of 400 kVA or less.

FIG. 6 shows a general configuration of a transistor inverter for driving an AC motor.

In Figure 6, DC power supply 1 and filter capacitor 2
A power source consisting of is supplied to a transistor bridge 4 through a high-speed fuse 3, and an electric motor 5 is driven by its AC output.

The transistors currently used for this purpose are mainly modular, with the main electrode and cooling surface electrically insulated.
The main electrode is connected to the transistor chip via a bonding wire.

Figure 3 shows an example of the structure of a module type transistor, in which an insulating ceramic 81 with good thermal conductivity is bonded on a copper base 80 that dissipates heat to cooling fins, and copper materials 82, 83, 84 are bonded on top of it. The collector of the transistor pellet 85 is bonded to the copper material 82 with the emitter terminal facing upward, the emitter terminal is bonded to the emitter electrode 89 with the bonding wire 87, and the collector side is bonded to the collector electrode 88 with the bonding wire 86. It is connected.

If one of the upper and lower transistors becomes punctured, the DC power supply is short-circuited and an overcurrent flows through the transistor.

Since the bonding wire may melt and generate an arc, causing the outer wall of the module type transistor to scatter and become dangerous, a high-speed fuse 3 is used to cut off the fault current.

As the capacity of the inverter increases, it is necessary to use a large number of module elements in parallel.In this case, in order to prevent the outer wall of the module elements from bursting, a high-speed fuse must be connected to the collector side of each transistor module, as shown in Figure 7. are doing.

This is because there is no fuse suitable for the fault current of the module elements connected in parallel as the common fuse 3 on the DC side as shown in FIG.

Also, in Figure 7, fuses are inserted on the collector side of each transistor, but this is because the base drive signal of the transistor is applied as a common signal between the emitter and base of each transistor, so the impedance on the emitter side is reduced as much as possible. This is because it needs to be lowered.

FIG. 7 shows one phase of a transistor bridge, in which the emitters and bases of a plurality of transistors 61-1 to 61-n are connected in parallel, and high-speed fuses 31-1 to 31-n are connected to each transistor. n is inserted.

Similarly, the bases and emitters of the transistors 62-1 to 62-n are connected in parallel, and
High speed fuses 32-1 to 32 for each transistor
-n is inserted.

Furthermore, the capacitor 8 is placed as close to the element as possible in order to absorb surges from the DC bus.

(Problem to be Solved by the Invention) However, if a fuse is connected to the collector side of each transistor as shown in FIG. 7, the wiring length becomes long and the inductance L increases, resulting in a surge voltage CL d l at turn-off. There is a problem in that the reliability of the element t decreases due to the increase in t.

In particular, recently developed IGBT and MCT (MOS)
Controlled Thyristor) etc.
Since the switching speed is several times faster than that of a bipolar transistor, the di/dt is also several times higher (5 to 6 times).
The surge voltage increases accordingly, making conventional circuit methods unusable.

For this reason, a surge voltage absorption circuit as shown in FIG. 8 has been used.

In FIG. 8, wiring inductances La and Lb.

When Lc and Ld are present in the main circuit of each IGBT71.72, the surge energy between the collector and emitter of the IGBT71 is clamped by the capacitor 9 and diode 10, and is discharged to the capacitor 2 via the resistor 16. Also, the diode 11. for the IGBT72. The surge energy is clamped by the capacitor 12 and discharged to the capacitor 2 via the resistor 15.

However, the disadvantages of this circuit are that it becomes complicated due to the increased number of parts used, that a surge clamp circuit must be provided for each element, and that energy loss occurs in the resistors 15 and 16.

One way to solve the above drawbacks is to suppress the increase in inductance due to the insertion of high speed fuses.

The present invention is a protection circuit for a transistor bridge that takes into consideration the insertion position of a fuse so as to suppress an increase in inductance due to the insertion of a high-speed fuse, and also allows a simple circuit to absorb the energy equivalent to the inductance due to the insertion of a fuse. is intended to provide.

[Structure of the invention]

(Means and Effects for Solving the Problems) The present invention inserts a high-speed fuse on the collector side of the transistor connected to the positive electrode side of the DC bus of the bridge-connected module type transistor, and also connects the high-speed fuse and the collector of the transistor. A snubber capacitor is connected between the connection point of The surge energy caused by this is absorbed by the snubber capacitor, and the fault current from the load is quickly cut off by the high-speed fuse provided on the output side of the bridge, thereby preventing the outer wall of the module element from bursting.

(Example) An example of the present invention is shown in FIG. In FIG. 1, the same parts as in conventional FIGS. 7 and 8 are given the same numbers, and their explanations are omitted. Note that FIG. 1 shows one phase of the inverter bridge.

In Figure 1, the positive pole side of the DC bus is connected to the fuse 31-1.
~31-n through IGBT71-1~71 respectively
- connected to the collector of IGBT71-1 to 71-
The emitter side of n is connected in parallel, and IGBT72-1 to 7
2-n collectors in parallel connection. Further, the emitters of the IGBTs 72-1 to 72-n are connected in parallel with each other and connected to the negative electrode side of the DC bus.

Further, each gate of IGBTs 71-1 to 71-n and each gate of IGBTs 72-1 to 72-n are also connected in parallel, and a common drive signal is applied to each gate.

Further, the collectors of IGBTs 71-1 to 71-n are connected to the negative electrode side of the DC bus through capacitors 8-1 to 8-n, respectively.

Figure 2 shows an equivalent circuit including the stray inductance L due to the installation of the fuse 31.
1 or 72 is turned off, the energy of the stray inductance L is bypassed to the capacitor 8, and I G B
The inductance can be reduced by connecting the emitter of T71 and the collector of IGBT72 as close as possible using a conductor with a large surface area.

If the IGBT deteriorates and becomes short-circuited 1. For example, I
If some of G B T71-1 to 71-n are short-circuited,
When the IGBTs 72-1 to 72-n are turned on, the DC power supply becomes momentarily short-circuited and an overcurrent flows.

In this case, an overcurrent protection circuit operates inside the -shell.
The fault current is cut off through the gates of IGBTs 72-1 to 72-n.

In this case as well, reducing the stray inductance L is
It is important for the IGBT to interrupt current within a safe operating area when turned off.

The protection circuit does not operate and the IGBT72-1 to 72-
If n also suffers from a short circuit failure, fuses 31-1 to 31-n
The fuse 33 interrupts the short-circuit current from the DC power supply, and the fuse 33 interrupts the fault current from the load motor, thereby protecting the module elements from bursting due to arcing.

The most complicated failure occurs, for example, when only one IGBT 72-1 becomes short-circuited, and if the number of parallel elements is small, the fuses 31-1 to 31-n and 33 will melt and cut off the fault current. When there are many parallel elements, the fault current is small, so the emitter side of the IGBT 72-1 blows out before the fuse blows out.

In this case, as shown in FIG. 3, the bonding wire 86 has a good cooling effect and the bonding wire 87 has a poor cooling effect, so the bonding wire 87 is fused first. When the emitter side of IGBT72-1 starts to melt,
The gate potential of IGBT 72-1 rises. That is, in the case of a bipolar transistor, the gate is electrically connected, and in the case of an IGBT, the gate is insulated, but the withstand voltage is several tens of volts, so when the emitter starts blowing out, the collector potential is output to the gate.

This turns on other IGBTs connected in parallel, increasing the fault current, and blows out the fuses 31-1 to 31-n and 33 to cut off the fault current.
rupture can be prevented from occurring.

In addition, in the case of a transistor or IGBT in which the collector and emitter have opposite characteristics in FIG. 1, or in the case of an element having a gate drive circuit on the collector or anode side,
This can be handled by connecting a fuse to the negative pole side of the DC bus.

Further, as a bridge snubber circuit, it is also possible to use a diode and a capacitor as shown in FIG. 4, or to provide a snubber in each element as shown in FIG. Furthermore, as shown in FIG. 4, it is also possible to provide a fuse by grouping a plurality of elements.

〔Effect of the invention〕

As explained above, according to the present invention, by providing a fuse on only one pole, the inductance of the inverter bridge is reduced, making it possible to provide a margin for the safe operation area of switching and improving reliability. do.

Furthermore, even when the control circuit or elements deteriorate, the high-speed fuses, including the common fuses of the snubber circuit and the bridge, quickly cut off the fault current and prevent further failures of the module elements, protecting transistor bridges using module elements. It is extremely effective as a circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram for explaining the present invention in detail, FIG. 3 is a schematic structural diagram of a module type transistor, and FIGS. The figures are circuit diagrams showing other embodiments of the present invention, FIGS. 6 and 7 are circuit diagrams showing a conventional example, and FIG. 8 is an explanatory diagram of the conventional circuit. 1... DC power supply, 2... Capacitor, 3,
31.32.33...high speed fuse. 4...Transistor bridge, 5...Electric motor, 6
1.62...Transistor, 71.72...IG
BT, 8.9.12... Capacitor, 10, 11... Diode, 15.16... Resistor.

Claims (1)

[Claims] In a transistor bridge protection circuit in which multiple modular transistors connected in parallel are bridge-connected, a high-speed fuse is inserted into the collector side of each transistor connected to the positive pole side of the DC bus, and a high-speed fuse is inserted into the collector side of each transistor. A protection circuit for a transistor bridge, characterized in that a snubber circuit is connected between the connection point and the negative electrode side of the DC bus, and a common high-speed fuse is provided on the output side of the transistor bridge.