JPH0217858A - Protection circuit for self-extinguishing element - Google Patents

Abstract

PURPOSE:To protect a self-arc extinguishing element against an overcurrent damage by detecting an overcurrent of the element as an insulated output by means of a current transformer with a bias wiring, and performing current limiting control of the element by using the detection output. CONSTITUTION:A voltage type inverter is composed of a filter capacitor 3 of a DC power source, a current transformer 4 with a bias winding, self-arc extinguishing elements 5-10 for forming a 3-phase voltage inverter, and free wheel diodes 11-16 to drive an induction motor 17 of a load. The transformer 4 detects a current IC flowing out from the power source by the ignition and extinction of the element 5, detects an overcurrent and a phase short-circuit time, and protects the elements 5-10 against an overcurrent damage. In this case, the transformer 4 is composed of a current detecting winding 41, a core 42, a bias winding 43, output windings 461-466, etc. Thus, a predetermined overcurrent value can be set by the magnetomotive force of the winding 43 to eliminate the induction of a noise erroneous operation.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a protection circuit for self-extinguishing elements, and more particularly to a protection circuit for self-extinguishing elements.

Transistors and MOSFII! Base, like T etc.
Alternatively, the present invention relates to a protection circuit for a self-extinguishing element that can control collector or drain current using gate voltage and current.

[Conventional technology]

Many DC-AC or AC-DC power conversion devices using self-extinguishing elements have been put into practical use.
As an overcurrent protection device for such a power converter, Japanese Patent Laid-Open Publication No. 185064/1988 entitled "Drive Circuit for Electrostatic Induction Self-Extinguishing Element" is known. This JP-A-61-
The conventional device disclosed in Publication No. 185064 detects the terminal voltage caused by the overcurrent of the self-arc-extinguishing element, and controls the gate voltage of the self-arc-extinguishing element according to this terminal voltage, thereby suppressing the overcurrent flowing through the self-arc-extinguishing element. This protects the circuit by suppressing it and then cutting off the circuit.

[Problem to be solved by the invention]

In the above-mentioned prior art, (1) overcurrent detection is performed by detecting the collector voltage generated in the self-extinguishing element due to the flow of overcurrent; therefore, it is not possible to accurately obtain the set value of overcurrent.

(2) At turn-on, it is necessary to distinguish between the collector voltage due to turn-on delay and the collector voltage due to overcurrent.

(2) Since the gate voltage is controlled by directly detecting the collector voltage, which varies between several volts and several hundred volts, there is a risk of malfunction due to noise.

There were other problems.

The purpose of the present invention is to detect the overcurrent flowing through the self-extinguishing element in an insulated state by comparing it with a set overcurrent value, and to control the gate (or base) voltage and current of the self-extinguishing element using the detection output. There is a particular thing.

[Means to solve the problem]

The above purpose is to use a current transformer with a bias winding, set the overcurrent by the magnetomotive force of this bias winding, and set the overcurrent by the magnetomotive force of the self-extinguishing element current that flows with the opposite polarity to the magnetomotive force of this bias winding. This is achieved by controlling the gate (or base) voltage and current of the self-extinguishing element using the output of the current transformer generated by canceling the bias magnetomotive force.

[Effect]

A current transformer with a bias winding can set the required overcurrent value by the magnetomotive force of the bias winding, and the current transformer output, which is the overcurrent detection output, is isolated from the main circuit, so noise malfunctions are avoided. There is no need to worry about triggering.

Furthermore, since overcurrent is directly detected, the above-described determination at turn-on is not necessary.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1,
2 are the positive and negative poles of a DC power supply (not shown).

3 is a filter capacitor, 4 is a current transformer with bias winding,
5 to 10 are self-extinguishing elements constituting a three-phase voltage type inverter, 11 to 16 are freewheel diodes connected in antiparallel to the self-extinguishing elements to circulate the current of the load, and 17 is an induction motor of the load. For example, the phase current Iυ flowing through the induction motor 17 flows as shown by the solid line due to the ignition of the self-arc extinguishing elements 5 and 8, and also flows through the freewheel diode 12 as shown by the broken line due to the extinguishing of the self-arc extinguishing element 5. It circulates through. Therefore, when the self-arc extinguishing element 5 is turned on, a current for canceling the current shown by the broken line flowing through the freewheeling diode 12 and recovering the freewheeling diode 12 is superimposed on the current shown by the solid line flowing through the self-arc-extinguishing element 5. do.

Therefore, the power supply side (
The current Ic flowing out from the filter capacitor 3 (including the filter capacitor 3) is as shown in FIG. 4(a).

The current transformer 4 with bias winding detects this current Ic+, detects an overcurrent flowing through the load, or an overcurrent in the event of a phase short circuit (for example, when both self-extinguishing elements 5 and 6 are conductive), and performs self-extinguishing. This protects the arc element from damage due to overcurrent. In the current transformer 4 with bias winding, 41 is a current detection winding that detects the current flowing through the self-extinguishing element, 42 is an iron core, and 43
is a bias winding, 44 and 45 are resistors and power supplies for setting overcurrent values, and 461 to 466 are output windings provided corresponding to self-extinguishing elements 5 to 10 forming the inverter, 471 to 476 and 481 to 486 are diodes and resistors constituting the output circuit.

Here, let the overcurrent value that must be protected be 〇.

First, a current Io is caused to flow through the bias winding 43 by the power supply 45 and resistor 44 of the bias circuit.

If the number of turns of the bias winding 43 is No, then the magnetomotive force due to the bias winding 43 will be 0.No. Next, a current Ic is caused to flow through the current detection winding 41 so that the magnetomotive force has a polarity opposite to that of the bias magnetomotive force. If the number of turns of the current detection winding 41 is No, then the magnetomotive force due to the current detection winding 41 will be IC-ND.

The operation of detecting an overcurrent flowing through the self-arc-extinguishing element based on the relationship between these magnetomotive forces will be explained with reference to FIG. The iron core 42 of the current transformer 4 with bias winding is saturated in the positive direction due to the magnetomotive force 10-NB of the bias winding 43, as shown in FIG. 2, for example.

When the voltage type inverter is controlled, the current Ic flowing from the power supply side to the self-arc extinguishing elements 5 to 10 passes through the current detector 41, and the magnetomotive force IC-ND is in the direction of canceling the bias magnetomotive force 0 and NB. Become. Then, when the magnetomotive force Ic-No of the current detection winding 41 becomes approximately equal to the bias magnetomotive force Ic-NB, the iron core 42 goes from saturated to unsaturated, and performs a current transformer operation. This current transformer operation becomes even more remarkable when the magnetomotive force Ic-No of the current detection winding 41>bias magnetomotive force Io-NB, and the output windings 461 to 466
produces a magnetomotive force proportional to (IC-NO-Io-NB). The magnetomotive force generated in the output windings 461-466 is taken out as a voltage to the resistors 481-486 via the diodes 471-476.

That is, in the current transformer 4 with a bias winding that produces an output when the magnetomotive force IC-ND of the current detection winding 41 and the bias magnetomotive force 10-NB become equal, the overcurrent Ic flowing through the self-extinguishing elements 5 to 10 is reduced to N. .

It can be detected as

Next, the operation of controlling the overcurrent flowing through the self-extinguishing element 5, for example, by the overcurrent detection output of the bias winding current transformer 4 will be explained using FIGS. 3 and 4. . In FIG. 3, 18 is the gate resistance of the self-extinguishing element 5, 19 and 20 are resistors and transistors for voltage division control of the gate voltage of the self-extinguishing element 5, and 21 is the transistor 2.
0 base resistor, 22 is a gate driver for the self-extinguishing element 5, 23 is a photocoupler for inputting an isolated PWM signal to the gate driver 22, 24 is a transistor for input signal of the photocoupler, 25 is an AND circuit, 26 is P
WM signal generation circuit, 27 is a PWM signal stop circuit using overcurrent detection output 481, 28 is a photocoupler for inputting an isolated signal to PWM signal stop circuit 27, 29 is overcurrent detection output 481 that continues for a predetermined time This is a circuit that supplies an input signal to the photocoupler 328. Also,
In FIG. 4, (a) shows self-extinguishing elements 5 to 5 from the power supply side.
Waveform of current Ic flowing through 10, (b) is output voltage Vo of current transformer 4 with bias winding (voltage of resistors 481 to 486)
(Q) shows the waveform of the gate voltage of the self-extinguishing element 5.

During the control of the self-extinguishing element 5, for example, if the self-extinguishing elements 5 to 10 are erroneously turned on due to noise, the overcurrent IC
' occurs (Fig. 4 (a)), an overcurrent detection output Vo (Fig. 4 (b)) is generated in the current transformer 4 with bias winding, and the third
In the circuit shown, transistor 20 becomes conductive. Due to the conduction of the transistor 20, the gate voltage of the self-extinguishing element 5 is controlled by the gate resistor 18 and the resistor 19, and the current overload determined by the gate voltage V a (FIG. 4(C)) controlled by the gate resistor 19 is controlled by the gate resistor 18 and the resistor 19. Current can be suppressed. For example, if a self-extinguishing element 54, -IGBT (500V, 100A element) is adopted, from the characteristic diagram in FIG.
By setting the gate voltage Va to 6V, the overcurrent flowing at 200A or more at 15V can be controlled to be limited to about 7OA. If the overcurrent is temporary, the overcurrent detection output Vo of the bias winding current transformer 4 disappears, so the current limiting control is canceled and the normal control state returns.

If the overcurrent continues for a long time, current limiting control will also continue. During this current-limiting control, current flows through the self-extinguishing element 5 with a voltage applied between its terminals, so the loss of the element is extremely large, and if left unchecked, there is a risk of damaging the element. . Therefore, if the overcurrent continues for a predetermined period of time, it is necessary to quickly extinguish the self-extinguishing element. In this case, by supplying the output of the circuit 29 that detects that the overcurrent detection output Vo has continued for a predetermined period of time as shown in FIG. 3 to the PWM signal stop circuit 27 via the photocoupler 28, It is sufficient to stop the PWM signal.

Note that the means for detecting that overcurrent continues for a predetermined period of time is as follows:
It is also possible to add one more set of output windings to the current transformer 4 with bias winding, and compare and detect the outputs of this by the circuit 29. In this case, the photocoupler 28 may be omitted since an isolated output is obtained.

In the above explanation, the current Ic flowing from the power supply side to the self-arc extinguishing element 5 which constitutes the inverter is detected and the self-arc extinguishing element 5 is controlled to be current-limited. However, in this embodiment, the bias winding The self-arc-extinguishing elements 6-10 are also current-limited at the same time by the other outputs 482-486 of the wired current transformers. Therefore, the - set of overcurrent detection devices can perform current limiting control on all self-extinguishing elements, which is effective in suppressing overcurrent.

According to this embodiment, the overcurrent flowing through the self-arc-extinguishing element is detected as an insulated output, and the self-arc-extinguishing element through which the overcurrent is flowing can be current-limited by the detection output. Can be protected from current damage.

Other embodiments are shown in FIGS. 5 and 6. In the embodiment shown in FIG. 1, a separate power supply is provided to supply the current of the bias winding. This embodiment has the disadvantage of requiring a separate power supply. FIG. 5 shows an example in which the bias winding current is supplied from the main and sub power supply to the chopper using the transistor 18 using a circuit, and FIG. 6 shows an example in which the bias winding current is supplied directly from the main circuit power supply via a resistor. This embodiment has the advantage of not requiring a separate power source compared to the embodiment of FIG.

Still other embodiments are shown in FIGS. 7 and 8.

In the embodiment shown in FIG. 1, a set of current transformers with bias windings is used to control current limiting of all self-extinguishing elements. This embodiment has the disadvantage that current-limiting control is performed even in elements to which no overcurrent actually flows. 7 and 8 show examples in which a current transformer with a bias winding is provided for each self-extinguishing element, and current limiting control is performed only on the element through which overcurrent is actually flowing. The figure shows an embodiment in which the power source of the bias winding circuit is shared by the upper and lower arms of each phase.

Further, FIG. 9 shows the VOE-VCE characteristic of an IGBT, which is one of the self-extinguishing elements.

Note that the present invention is not limited to the above-described embodiments, and may be applied to current transformers with bias windings provided in each phase to control current limiting of upper and lower arm elements together, or bias winding circuits. An example may be considered in which the power source is shared by all current transformers with bias windings. Furthermore, as the current flowing through the self-extinguishing element increases, the magnetomotive force of the input winding increases, and the loss of the bias circuit that sets the overcurrent value increases accordingly. The current flowing through the element may be divided and supplied to the input winding.

〔Effect of the invention〕

According to the present invention, an overcurrent flowing through a self-extinguishing element is detected by a current transformer with a bias winding through an insulated output.
Since the self-arc-extinguishing element can be subjected to current-limiting control using this detection output, the self-arc-extinguishing element can be protected from overcurrent damage.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is an operating characteristic diagram of the current transformer with bias winding used in the circuit shown in Fig. 1, and Fig. 3 is a self-extinguishing element in the circuit shown in Fig. 1. Current limiting control circuit diagram,
FIG. 4 is an explanatory diagram of the current limiting control of the self-extinguishing element, FIGS. 5 to 8 are circuit diagrams showing other embodiments of the present invention, and FIG.
The figure shows the VOE and VCE characteristics of the IGBT. 4...Current transformer with bias winding, 481-486...
Overcurrent detection output, 5 to 10... Self-extinguishing element, 18.
. . . Gate resistance of self-extinguishing element, 19 . . . Resistor for gate voltage division, 20 . . . Transistor for gate voltage division. l Figure 2 Figure 5 Figure 6 Figure 3 Figure 4 Figure 7 Section 8 Figure 9 QE

Claims (1)

[Claims] 1. A self-extinguishing element that can control the current flowing through the element by controlling the voltage and current of the gate or base;
An output is output to the output winding from the point in time when the magnetomotive force of the input winding and the magnetomotive force of the bias winding, which are provided with an input winding, an output winding, and a bias winding and have a relationship of opposite polarity, are approximately equal to each other. A current is generated in the current transformer by passing a current flowing through the self-arc-extinguishing element through the input winding of the current transformer and a current corresponding to the overcurrent set value through the bias winding. A self-arc-extinguishing element protection circuit, characterized in that current-limiting control of the self-arc-extinguishing element is performed by the output of the self-arc-extinguishing element. 2. A protection circuit for a self-arc-extinguishing element according to claim 1, wherein the self-arc-extinguishing element is turned off when the output of the current transformer continues for a predetermined period of time.