JP2002330580A - Electric power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce switching loss, and shorten the setting time of dead time. SOLUTION: Switching time of an element T1 at the low-current turn-off is shortened, by charging the output capacity of the element T1 with energy stored in the inductance L at the turn-off, by connecting a booster chopper circuit comprising an inductance L, switching elements M1 and M2 in parallel with a switching element T1 (IGBT) for the inverter and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter such as an inverter for driving a motor or the like, and more particularly to an improvement thereof.

[0002]

2. Description of the Related Art FIG. 3 shows an IGBT as a power semiconductor device.
A general example of an inverter using (insulated gate bipolar transistor) will be described. In the figure, reference numeral 1 denotes a DC power supply circuit (in the case of AC input, a rectifier + electrolytic capacitor configuration), 2 denotes an inverter circuit composed of an IGBT and a diode and converts DC to AC, and 3A and 3B drive the IGBT gate. Circuits, 4A and 4B are power supplies for the gate drive circuit, 5 is a control circuit that outputs an ON / OFF command signal to each gate drive circuit, and 6 is a load such as a motor.

Normally, when commutation occurs during inverter operation, the upper and lower arms are simultaneously turned on because of variations in signal transmission time of the gate drive circuit in the upper and lower arms, variations in IGBT element characteristics, and storage time during switching. It is necessary to set a short-circuit prevention period (dead time) so as not to occur. In the case of an IGBT, this time is usually set to 3 to 5 μs.

[0004]

When the IGBT is turned off, for example, as shown in FIG. 4, the voltage change rate dv / dt of the voltage (VCE) applied between the collector and the emitter depends on the current value to be turned off. The smaller the turn-off current value, the lower the dv / dt value (FIG. 4A shows the case where the turn-off current is large, and FIG. 4B shows the case where it is small). This is because the output capacitance of the IGBT to be turned off is charged by the turn-off current, and the smaller the turn-off current value, the longer the time required for charging.

Normally, when the IGBT is turned off at a current value of about several hundredths or less of the rated current of the IGBT, dv / dt is extremely reduced, and it takes several μs to reach the DC power supply voltage value (turn-off switching time). Is extended). Therefore, in a device that sets a short dead time,
IGBT that turns off when turning off at low current value
Before the voltage applied to the IGBT reaches the DC power supply voltage value, the IGBT on the opposite arm is turned on, and the upper and lower arm short-circuit phenomenon occurs instantaneously. As a result, problems such as unnecessary overcurrent detection and an increase in switching loss of the IGBT occur.

On the other hand, the above phenomenon can be avoided by increasing the set time of the dead time. However, from the viewpoint of controlling the motor, the voltage actually output by the inverter is reduced by the dead time, so that the accuracy is high. You lose control. Particularly, in the high carrier operation and the low speed operation, the error voltage between the command voltage and the actual output voltage becomes relatively large, so that there is a problem that torque ripple and rotation unevenness of the motor become large. Accordingly, it is an object of the present invention to reduce the switching time at low current, reduce the switching loss of the IGBT, and shorten the dead time setting time.

[0007]

According to the first aspect of the present invention, a boost chopper circuit is connected in parallel with a power semiconductor element constituting a power conversion circuit.
By charging the output capacitance of the power semiconductor device with the energy of the boost chopper circuit, the switching time at the time of low current turn-off is reduced.
According to the first aspect of the present invention, the boost chopper circuit can be operated in synchronization with a turn-off command of the power semiconductor element (the second aspect of the invention).

That is, even when the turn-off current value of the IGBT is small, dv / dt is not reduced by converting the energy of the inductance in this circuit to the charging of the output capacitance of the IGBT by using the boost chopper circuit. It can be turned off in the same switching time as when turning off a large current.

[0009]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. As is apparent from FIG.
A boost chopper circuit including an inductance L and switch elements M1 and M2 is connected in parallel with the GBT (T1). As the power supply for the boost chopper circuit, the power supply 4A for the gate drive circuit is used. D is a blocking diode. In addition, for the signal C1 from the control circuit 5, the inverter gate IN and the one-shot circuits 7A and 7B of the rising edge trigger are connected.

The operation of FIG. 1 will be described with reference to FIG. Now, when the signal C1 from the control circuit 5 is turned off as shown in FIG. 2, the switch element M1 is in a one-shot period (t ₁ ), and the switch element M2 is in a one-shot period (t ₂ ).
Since on only (Fig. 2, reference), the inductance L, the voltage of the power source 4A as Vg, energy ^{_{E = LI 0 2/2 =}} Vg 2 t 1 2 / 2L (J) is accumulated. Thereafter, when M1 is turned off, the current flowing through the inductance L becomes the diode D
(See FIG. 2), the energy of the inductance is converted to energy for charging the output capacity of the IGBT.

As described above, by synchronizing the turn-on of M1 and M2 with the turn-off timing on the IGBT side, the inductance current can be used as the charging current for the output capacitance of the IGBT. , The switching time can be reduced. In the example of FIG. 1, the operation is performed every time the IGBT is turned off irrespective of the current value of the IGBT. However, in order to reduce the loss, a signal from the IGBT or a detector that detects the current flowing to the load is used. It is also possible to operate only when the current value is lower than a certain current value.

[0012]

According to the present invention, since the upper and lower arms are not short-circuited at the time of low current turn-off, erroneous detection of overcurrent can be avoided, and not only switching loss is reduced but also dead time is shortened. It is possible to realize high performance of motor control.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram of each part for explaining the operation of FIG. 1;

FIG. 3 is a configuration diagram showing a conventional example of an inverter main circuit.

FIG. 4 is a waveform diagram of each part for explaining the operation of FIG. 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Inverter circuit, 3A, 3B ... Gate drive circuit, 4A, 4B ... Gate drive circuit power supply, 5 ...
Control circuit, 6: motor (load), 7A, 7B: one-shot circuit, L: inductance, M1, M2: switch element, D: diode, T1: IGBT (insulated gate bipolar transistor), IN: inverter gate.

Claims (2)

[Claims] A boost chopper circuit is connected in parallel with a power semiconductor device constituting a power conversion circuit, and the output capacitance of the power semiconductor device is charged with the energy of the boost chopper circuit so that a low current turn-off time is achieved. A power conversion device characterized by shortening the switching time. 2. The power conversion device according to claim 1, wherein the boost chopper circuit operates in synchronization with a turn-off command of a power semiconductor device.