JPH04322173A - Bridge type converter protection apparatus - Google Patents

Abstract

PURPOSE:To safely cut off an over current by connecting in series a P-channel IGBT and an N-channel IGBT which ensures wider safe operation area than such P-channel IGBT and turning off the gates, if an over current is detected, of both P-channel IGBT and N-channel IGBT after limiting the over current with the N-channel IGBT. CONSTITUTION:Upon reception of an over current detecting signal el7, a gate control circuit 32 executes gate squeezing operation of N-channel IGBT (N) 22, 24, 26. Therefore, a current I is limited. During this period, a gate voltage is normally applied to the P-channel IGBT (P) 27, 28, 29. Accordingly, P27, 28, 29 are not deteriorated. Thereafter, a time delay circuit 31 outputs a signal e31, the gate voltages of N22, 24, 26 and P27, 28, 29 turn off and each element turns off to cut off an accident current. Thereby, since the current I is limited, P27, 28, 29 safely turn off.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a bridge type converter, which ensures more reliable overcurrent protection of self-extinguishing elements.

0002

2. Description of the Related Art The main circuit and protection circuit of a conventional voltage source inverter using IGBTs are shown in FIG. 7 and will be described below. A bridge circuit consisting of N-channel IGBTs 21 to 26 performs DC to AC conversion from a DC power source 1, and supplies power to a motor 5 via current detectors 3 and 4.

[0003] IGBTs 21, 23, 25 are driven by a drive power source 11.
, 12, 13 and drive circuits 14, 15, 16, and the IGBTs 22, 24, 26 share the drive power source 7 and are driven by drive circuits 8, 9, 10, respectively. The overcurrent detection circuit 17 receives the outputs of the current detectors 3, 4, and 6, and when this level exceeds a set value, outputs and holds the signal OC.

When the overcurrent detection circuit 17 does not detect an overcurrent, the AND gate 19 transmits the signal from the PWM control circuit 18 to the drive circuit, switches the IGBT bridge circuit, and drives the motor 5. When an overcurrent is detected, the AND gate 19 turns off all PWM signals and turns off the IGBT bridge in response to the signal OC, thereby providing protection.

[0005]

[Problem to be Solved by the Invention] In the bridge circuit of FIG. 7, the negative side IGBTs 22, 24, and 26 can be driven by one drive power supply 7, but the positive side IGBTs 21, 23, and 2
5, three insulated drive power supplies 11, 12, 13
is necessary. This increases cost for relatively small capacity converters. Therefore, the three IGBTs 21 and 23 on the positive side
, 25, it is conceivable to use P-channel elements and share the driving power source as in the negative side.

However, P-channel IGBTs fundamentally have the disadvantage of having a narrow safe operating area. Figure 8 shows the N-channel IG
An example of the characteristics of the safe operating area of BT and P-channel IGBT is shown. For N-channel IGBT, 10μs even in load short-circuit condition
If the device is turned off within a certain amount of time, the device can be protected. However, in a P-channel IGBT, as shown in FIG. 8, if a current exceeding 200% of the device rated current is turned off, the device deteriorates.

[0007] When a P-channel IGBT and an N-channel IGBT are connected in series for one phase of a bridge in this way, the safe operating area of the P-channel IGBT is narrow in the event of a load short circuit, and protection is difficult and reliability deteriorates. .

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an economical protection device for a bridge type converter that can cover the narrow safe operation area of a P-channel IGBT and protect it from overcurrent. purpose. [Structure of the invention]

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first self-extinguishing element and a current-limited device according to a drive signal, which is within a safe operating area than the first self-extinguishing element. When an overcurrent in the series circuit is detected, the overcurrent is suppressed by a drive signal of the second self-extinguishing element. A means is provided for turning off the first self-arc-extinguishing element and the second self-arc-extinguishing element after the current is limited.

0010

[Operation] When an overcurrent is detected, the above means reduces the gate voltage of the second self-arc-extinguishing element to limit the overcurrent, and then the first self-arc-extinguishing element and the second self-arc-extinguishing element Both gates are turned off to safely cut off overcurrent.

[0011]

Embodiment An embodiment of the present invention is shown in FIG. 1 and will be described below. Note that parts that overlap with those in FIG. 7 are denoted by the same numbers, and explanations thereof will be omitted.

In FIG. 1, a three-phase inverter bridge is constructed in which P-channel IGBTs 27, 28, and 29 are connected to the positive side of DC power supply 1, and N-channel IGBTs 22, 24, and 26 are connected to the negative side. Drive circuits 14, 15, 16 are connected to P-channel IGBTs 27, 28, 2 by drive power supply 20.
9 respectively.

The overcurrent detection circuit 17 outputs an overcurrent signal e17, the gate aperture circuit 30 outputs a signal e30, and the N-channel IGBTs 22, 24,
26 gate voltages are controlled.

After the e17 signal, e31 is outputted via the time delay circuit 31, and the AND gate 19 performs a logical product with the output from the PWM control circuit 18, and outputs the signal e31 to the gate control circuit 3.
Stop sending PWM signals to 3 and 32. The gate control circuit 33 connects the P channel I via the drive circuits 14, 15, 16.
Turns GBT27, 28, and 29 on and off. The protection operation of the present invention will be explained using FIG. 2.

Now, the N-channel IGBT and P
VGE-N and V shown in FIG. 2 respectively in the channel IGBT.
Assuming that a gate signal GE-P is applied and the load is short-circuited, the current I flowing through the IGBT at time t0 increases in the direction of the broken line as shown in FIG. Assuming that the latch-up breakdown point of a P-channel IGBT is Ilp, if a current exceeding this current is blocked by the gate, the element will deteriorate.

At time t1, overcurrent detection signal e17
In response, the gate control circuit 32 lowers VGE-N to N
A gate narrowing operation of the channel IGBT is performed. Figure 9
As is clear from the VCE-Ic characteristics of the IGBT, V
When GE is lowered, VCE increases, Ic is limited, and current I is limited. During this period, VGE-P is normally added to the P-channel IGBT, so the P-channel IGBT
The VCE of BT becomes low and the P-channel IGBT does not deteriorate.

Thereafter, at time t2, the time delay circuit 31 outputs the signal e31, and the N-channel IG
Gate voltage of BT and P-channel IGBT VGE-N, V
Both GE-Ps are turned off, and each element is turned off to cut off the fault current. In this case, since the current I is limited, the P-channel IGBT is safely turned off.

In FIG. 2, the peak value of I is less than Ilp, but in actual circuits, a filter is provided in the overcurrent detection circuit 17 for the purpose of noise prevention, and due to signal transmission delays, etc., I (current) becomes less than Ilp. In some cases, the drive signal of the P-channel IGBT remains on, and the gate voltage of the N-channel IGBT is lowered to limit the current, and when the current becomes less than Ilp, the P-channel IGBT and N-channel IGBT are simultaneously turned off. Safe turn-off is possible.

According to the present invention, both IGBTs are turned off after the overcurrent in the P-channel IGBT, which has a narrow safe operating area, is limited by the gate voltage restriction of the N-channel IGBT, which has a wide safe operating area, resulting in safety and reliability. The good news is that by using P-channel and N-channel IGBTs and reducing the driving power supplies from the conventional four to two, a compact and economical bridge converter protection circuit can be established.

FIG. 3 shows a modification of FIG. 1, in which the overcurrent detection signal e
17, the output of the one-shot circuit 40 causes the protection circuits 41 and 42 to output PWM via the AND gate 19.
It is configured to temporarily hold the output of the control circuit 18.

[0021] The reason for this is that PWM
This is to avoid the risk of deteriorating the P-channel IGBT by entering a turn-off operation without limiting the overcurrent when an off signal is input to the P-channel IGBT, resulting in higher safety. Note that the protection circuit 42 on the N-channel side is not necessarily required.

Furthermore, as shown in FIG.
By connecting the T and N-channel IGBTs in reverse polarity, it becomes possible to apply positive and negative polarity biases to the gates by sharing the drive power supplies 7a and 7b. Furthermore, as shown in FIG. 5, a combination of MCT 52 and N-channel IGBT 22 is also possible.

FIG. 6 shows the on-voltage characteristics of the MCT. M.C.
Since T performs thyristor operation, the on-voltage is 1 to 1.5.
Although the loss during conduction is low, as low as V, there is a limit to the maximum turn-off current, and there is a drawback that a current beyond this cannot be turned off. In addition to IGBTs, there are transistors such as FETs, SITs, and bipolar transistors as elements that have a current-limiting effect depending on drive signals.

Thyristor-type self-extinguishing elements generally have a low off-state voltage, but have a limited maximum turn-off current. These elements include SITH, GTO, etc., and it goes without saying that these elements can be combined. Further, although the description has been made regarding two inverters connected in series, it goes without saying that there are no restrictions on the number of elements connected in series or the method of configuring the bridge. Furthermore, overcurrent detection can also be performed by utilizing the characteristic that the voltage between the electrodes of an IGBT or FET is saturated.

[0025]

Effects of the Invention According to the present invention, devices with a narrow safe operating area such as P-channel IGBTs, and elements with thyristor characteristics such as MCTs with low on-loss but limited maximum turn-off current and safe operating area wide transistor (I
A bridge converter is constructed by arranging elements in series whose current is limited by the magnitude of the drive signal such as GBT). After detecting an overcurrent, the drive signal of the element with a wide safe operation area is throttled to limit the fault current. By turning off all elements, it is possible to provide a protection circuit for a bridge converter that can safely protect a small, lightweight, low-loss bridge converter.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the above embodiment.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a third embodiment of the present invention.

FIG. 5 is a diagram showing a fourth embodiment of the present invention.

FIG. 6 is a voltage-current characteristic diagram of MCT.

FIG. 7 is a configuration diagram of a conventional device.

FIG. 8 is a characteristic diagram showing a safe operating area of an IGBT.

[Figure 9] IC- with IGBT VGE as a parameter
VCE characteristic diagram.

[Explanation of symbols]

1... DC power supply, 5... Electric motor, 3, 4,
6... Current detector, 7, 11, 12, 13, 20... Drive power supply, 8, 9, 10, 14, 15, 16... Drive circuit, 17... Overcurrent detection circuit, 18... PWM control circuit, 19... And Gate, 21 to 26... N-channel IGBT, 27, 28, 29... P-channel IGBT, 30... Gate aperture circuit, 31... Time delay circuit, 32, 33... Gate control circuit,
40... One-shot circuit, 41, 42... Holding circuit.

Claims (1)

[Claims] 1. A first self-extinguishing element and a second self-extinguishing element whose current is limited according to a drive signal and whose safe operating range is wider than that of the first self-extinguishing element are connected in series. When an overcurrent in the series circuit is detected, the overcurrent is limited by a drive signal of the second self-arc-extinguishing element, and then the first self-arc-extinguishing element and a means for turning off the second self-extinguishing element.