JP2919033B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a power converter in which power semiconductor devices are connected in series.

(Prior Art) In recent years, power semiconductor devices are on the cusp of increasing performance and capacity. In particular, IGBT (Insulated Gate Bipolat Tra)
nsistor) and power MOSFETs require less gate drive power, have a higher switching frequency, and can perform high-performance power conversion. Further, the voltage and current capacities of devices are steadily increasing, and are often applied to power converters of small and medium capacities.
In a converter using these devices, there is a method in which a snubber circuit is provided for each device, but a method in which a snubber circuit is not provided and provided collectively between DC terminals is also applied. FIG. 3 shows an example of the configuration, which is described, for example, on page 38 of “Semiconductor Power Conversion Circuit” edited by the Institute of Electrical Engineers of Japan, Special Committee on Semiconductor Power Conversion Systems. In FIG. 3, 1 is a DC power supply, 2 is an inverter circuit, 3 is an AC output, 4 is a snubber circuit, 41 is a snubber capacitor, 42 is a snubber resistor, and 43 is a snubber diode. In this circuit, the snubber capacitor 41 is always charged with the same voltage as the DC voltage. When the device is turned on or off, a surge voltage is generated. The capacitor 41 is charged via the snubber diode 43 by an amount corresponding to the surge voltage higher than the DC voltage. The loss of the snubber resistor 42 is not so large because it is only when the capacitor is discharged after the surge voltage rises. This circuit is called a DC snubber circuit.

When trying to configure a large capacity converter using IGBTs and power MOSFETs, a method of multiplexing multiple sets of converters to increase capacity and connecting devices in parallel or in series with one set of converters There is a method. When a high voltage converter is required and devices are connected in series, a snubber circuit shown in FIG. 4 is generally used. FIG. 4 shows one arm composed of a thyristor.
51 to 53 are thyristors, 411 to 413 are snubber capacitors, 42
1 to 423 are snubber resistors, and 441 to 443 are parallel resistors. The parallel resistor is provided for the purpose of balancing the voltage in a steady state. That is, when a voltage is applied to the illustrated thyristor in an off state, a leak current flows, and this value slightly differs for each device. For this reason, when there is no parallel resistance, a device having a larger leakage current has a smaller voltage distribution, and the voltage is concentrated on an element having a smaller leakage current. It is the role of the parallel resistor to equalize this static voltage distribution. The snubber capacitor and the snubber resistor have a function of suppressing a surge voltage at the time of turn-on / turn-off, and a function of maintaining a transient voltage balance of each device. The snubber capacitor is charged / discharged to almost zero voltage and the maximum voltage when the device is turned off every time the device is switched.

(Problems to be Solved by the Invention) When devices having a high switching speed are connected in series, the wiring becomes long due to structural restrictions of the devices, and the stray inductance increases. For this reason, there is a method of increasing the capacitance of a conventional configuration including a snubber resistor and a snubber capacitor, suppressing a surge voltage accompanying switching, and achieving a transient voltage balance. However, devices such as IGBTs are often driven at a high frequency. When the capacitance of the capacitor is increased, the loss of the resistance is increased and the effectiveness of the converter is reduced.

The present invention has been made in view of the above points, and has as its object to realize a snubber circuit suitable for a power converter in which high-speed switching power semiconductor devices are connected in series.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, in a converter in which two sets of arms are directly connected, each arm has a plurality of power semiconductor devices connected in series. Is provided with a conventional snubber circuit. In addition, DC between the positive terminal on the positive DC terminal side and the negative terminal on the negative DC terminal side of the device counted one each from the positive DC terminal and the negative DC terminal counting from the AC terminal. A snubber circuit is provided.

(Operation) With the above configuration, the normal voltage of the DC snubber circuit is proportional to a value obtained by dividing the DC voltage by the number of series devices. Assuming that this value is V, V is applied to the DC snubber capacitor of the device closest to the AC terminal, and 2 V is applied to the capacitor of the next device, and the DC snubber capacitor provided in the device closest to the DC terminal Is applied with a DC voltage as it is. The surge voltage accompanying the switching of the device is absorbed by this capacitor. Discharge due to a rise in the voltage of the capacitor is performed via a parallel resistor provided in parallel with the device or a conventional snubber circuit.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention,
Are connected in series to show two sets of arms. In FIG. 1, 411 to 414 are snubber capacitors, 421 to 424 are snubber resistors, 441 to 444 are parallel resistors, 451 and 452 are DC snubber capacitors, 462 is a DC snubber resistor, 472 is a DC snubber diode, 511 to 514 are IGBTs, 521 ~ 524 is a feedback diode,
6 is a positive DC terminal, 7 is a negative DC terminal, and 8 is an AC terminal.

The arm pair shown in FIG. 1 corresponds to, for example, one phase of a voltage source inverter. The operation is as follows: while IGBTs 511 and 512 are on, IGBTs 513 and 514 are off and then on
The off state is reversed and these states are repeated. Since the IGBTs 512 and 513 are alternately turned on, a voltage of the DC snubber capacitor 451 is constantly applied to half the DC voltage. The voltage between the DC terminals is directly applied to the other DC snubber capacitor 452. At the time of switching, the energy of the stray inductance of the wiring influences and an overvoltage is about to be applied to the semiconductor device, but this energy is charged to the DC snubber capacitor and the snubber capacitor attached to each device. Since the DC snubber capacitor basically fluctuates only in surge voltage, the capacitor may be larger than the capacitor attached to each device, so that most of the energy is charged in this capacitor. Discharge to a steady voltage is performed via a snubber or a parallel resistor attached to each device.

Since the DC snubber mounted between the DC terminals has a low impedance between the terminals, the discharge is performed via the resistor 462 to suppress the vibration.

As described above, in this embodiment, a DC snubber is attached to each of the devices connected in series, so that a rise in the voltage of the device during switching can be suppressed.

(Other Embodiment) FIG. 2 is a block diagram showing another embodiment of the present invention, in which a snubber resistor and a snubber diode are omitted from the DC snubber circuit shown in FIG. The same elements as those in FIG. 1 correspond to the elements having the same numbers. In this system, only the capacitor 452 is provided as a DC snubber between DC terminals. In this embodiment, the basic operation is almost the same as that shown in FIG. 1, but the discharge up to the DC voltage after the voltage rise of the capacitor 452 is performed without any loss with some oscillation.

In FIG. 2, even if one of the snubber circuit and the parallel resistor provided for each device is omitted, the DC snubber capacitor can be discharged.

〔The invention's effect〕

As described above, according to the present invention, a voltage surge at the time of switching can be suppressed by providing a DC snubber for each device connected in series. When the voltage of the converter is given, the number of series devices is usually determined by the sum of the applied voltage and the surge voltage.However, since the surge voltage decreases, the number of series devices can be reduced. Can be raised.

[Brief description of the drawings]

FIG. 1 is a block diagram of a power converter according to one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is a circuit diagram of a DC snubber circuit, and FIG. It is a circuit diagram of the conventional snubber circuit of a connection element. 1 DC power supply 2 Inverter 3 AC output 4 Snubber circuit 6 Positive DC terminal 7 Negative DC terminal 8 AC terminal

Claims (1)

(57) [Claims] 1. An arm comprising a plurality of power semiconductor elements connected in series is connected in series between a positive DC terminal and a negative DC terminal of a DC power supply. In a power converter having a connection point as an AC terminal, a first snubber circuit connected in parallel to the semiconductor element;
One end of the semiconductor element connected to the AC terminal 2
And a second snubber circuit provided between the other ends of the two semiconductor elements.