JPS63140672A - Power converter - Google Patents

Abstract

PURPOSE:To upgrade an apparatus for high performance, by turning ON one of the series-connected semiconductor circuits while others are in the period of turning OFF, and by suppressing the large current flow due to arm shorts by means of a saturable transformer inserted in series. CONSTITUTION:Four sets of cascode-connected semiconductor switching circuits 30-60 composed of a bipolar transistor and a MOSFET in direct connection are connected in a single-phase bridge. By ON-OFF operating switching circuits 30-60 in sequence, the power of a DC power source 10 is converted into AC power to supply to a load 20. Saturable transformers 31-61, in which the secondary winding as current suppressing means is shorted by resistances 36-66, are connected in series to the respective switching circuits 30-60. The ON-OFF signal to the switching circuit 50 is given to the bipolar transistor from a base drive circuit 52 through a signal insulation circuit 54 and to the MOSFET from a gate drive circuit 53, with which the switching circuits 30-60 are driven and controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a power conversion device using a cascode-connected semiconductor switch circuit configured by cascode-connecting a bipolar transistor and a metal oxide semiconductor field effect transistor. Regarding.

[Conventional technology]

For example, a power conversion device that converts direct current to alternating current, a so-called inverter, performs power conversion by sequentially turning on and off switching elements connected in a bridge. In particular, a switching element capable of switching at high frequencies is desired.

FIG. 3 is a circuit diagram showing an example of a cascode-connected semiconductor switch circuit, in which a bipolar transistor 3 with good large current characteristics and a metal oxide semiconductor field effect transistor (hereinafter MOS FE) with good high-speed switching characteristics are used.
A cascode-connected semiconductor switch circuit 2 is formed by connecting 4 (abbreviated as T) in series, and further connecting a diode 5 (or a constant voltage diode) and a flywheel diode 6 as shown. .

The on/off operation of the cascode-connected semiconductor switch circuit 2 is performed as follows. That is, an ignition signal is applied to the bipolar transistor 3 via the base drive circuit 7, and at the same time, the ignition signal is applied to the MOS FE via the gate drive circuit 8.
When both are turned on by applying an ignition signal to T4, a current flows from the positive side to the negative side of the cascode-connected semiconductor switch circuit 2. In order to cut off this current, bipolar transistor 3 and MOS FET 4
When the ignition signal applied to is removed, the high-speed switching MOS FET 4 is turned off first, so the current that was flowing until now is diverted to a path that bypasses this MOS FET, that is, the collector of the bipolar transistor 3 and the base of the bipolar transistor 30. Since the current flows through the path of →diode 5 →source side of MO3FET 4, bipolar transistor 3 can also be turned off safely and at high speed.

[Problem that the invention seeks to solve]

However, if the current flowing through the circuit becomes zero before turning off the cascade-connected semiconductor switch circuit 2 which is in the on state, by removing the ignition signal, the bipolar Since the current that should flow from the collector to the base of the transistor 3 is zero, the carriers injected from the base do not disappear quickly, so the turn-off time of the bipolar transistor 3 becomes long. Therefore, if the cascode-connected semiconductor switch circuit of the other arm connected in series is fired before the bipolar transistor 3 is turned off, a so-called arm short circuit may occur and an excessive current may flow, damaging the element. Such inconveniences may occur. Therefore, in order to prevent such arm short-circuit accidents, a signal delay element is provided so that the firing signal is not given to the other arm until a certain period of time has passed after the firing signal of one arm is removed. , the switching operation at high frequencies will be inhibited, and the bipolar transistor 3 and MOS FE
This results in a disadvantage that the characteristics of the cascode-connected semiconductor switch circuit 2 configured with T4 are lost.

Therefore, this invention combines bipolar transistors and MOS
Provides a power conversion device that uses a cascode-connected semiconductor switch circuit configured with a series connection with an FET to perform switching operation at a high frequency without generating excessive current that would damage the element in the event of an arm short circuit. The purpose is to

[Means for solving problems]

In order to achieve the above object, according to the present invention, a firing signal is applied to both a cascode-connected bipolar transistor and a metal oxide semiconductor field effect transistor to turn them on, and the firing signal to both is removed. By connecting two sets of cascode-connected semiconductor switch circuits that are turned off in series to a power supply, and repeating on and off operations of both cascode-connected semiconductor switch circuits alternately, the power converted from the connection point of both In a power conversion device configured to take out the means for causing the cascode-connected semiconductor switch circuit to alternately turn on the other cascode-connected semiconductor switch circuit during its turn-off period, or a separate saturable transformer for each cascode-connected semiconductor switch circuit; Instead of connecting in series, the primary winding having a center tap of a saturable transformer whose secondary winding is short-circuited by impedance is connected in series to the connection point of both the cascode-connected semiconductor switch circuits connected in series. The above object is also achieved by the insertion.

[Effect]

This invention connects two sets of cascode-connected semiconductor switch circuits each consisting of a bipolar transistor and a MOSFET connected in series to a power supply, and when one cascode-connected semiconductor switch circuit is on, the other cascode-connected semiconductor switch circuit is turned on. By alternately repeating the off state, when extracting the converted power from the connection point of both cascode-connected semiconductor switch circuits, it is possible to send an OFF signal to one of the cascode-connected semiconductor switch circuits without providing a signal delay element. By applying an on signal to the other bipolar transistor when it is in its turn-off period, the carriers in the bipolar transistor that is turned off are quickly extinguished, thereby realizing switching operation at a high frequency. The arm short-circuit current that occurs due to speed switching operation can be solved by inserting the primary winding of a saturable transformer whose secondary winding is short-circuited with an appropriate impedance into these cascode-connected semiconductor switch circuits in series. to prevent element damage. Also, instead of separately connecting a saturable transformer in series with both cascode-connected semiconductor switch circuits, a center-tapped saturable transformer is inserted at the connection point between the two, and the secondary winding of this saturable transformer is By short-circuiting with impedance, it is also possible to extract the converted power from the center tap of this saturable transformer while suppressing the arm short-circuit current.

〔Example〕

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

In FIG. 1, the DC power from the DC power supply 10 is It is converted into AC power and supplied to the load 20.

Here, each of the cascode connection switch circuits has the same configuration as the circuit diagram shown in FIG. Saturable transformers 31,41,51,61 are connected in series, each of which is short-circuited by a resistor 36,46,56,66 as impedance. Although a resistor is used in FIG. 1 as an impedance for short-circuiting the secondary winding of the saturable transformer, it is also possible to short-circuit the secondary winding using a reactor.

The on/off signal to the cascode connection switch circuit 50 connected to the positive side of the DC power supply 10 is sent to the signal isolation circuit 5.
4 to the bipolar transistor from the base drive circuit 52, and to the MOS FET from the gate drive circuit 5.
Given from 3. Furthermore, the same on/off signal as above is sent to the cascode connection switch circuit 60 connected to the negative pole side of the DC power supply 10 through the inverting element 65 and the signal isolation circuit 64.
The signal is applied from a base drive circuit 62 and a gate drive circuit 63 via. Other cascode connection switch circuit 30
Although not shown, circuits 40 and 40 are also provided with circuits configured similarly to those attached to the above-mentioned cascode connection switch circuits 50 and 60, so that on/off operations are performed. It has become.

With the circuit configuration shown in FIG. 1, for example, at the same time that the ignition signal to the positive side cascode connection switch circuit 5° in the on state is removed and the turn-off operation begins, the negative side cascode connection switch circuit 60 is Since the ignition signal is given, the current flowing through the positive side cascode connection switch circuit 50 immediately before this is zero, so the carriers injected from the base of the bipolar transistor do not disappear quickly and the turn-off time is shortened. Even if the length of the bipolar transistor becomes long, the cascode connection switch circuit 60 on the negative side is fired to actively flow current, thereby realizing quick turn-off of the bipolar transistor. However, the arm short-circuit current that flows during levering is caused by the saturable transformers 51 and 61 inserted in series in each cascode-connected switch circuit, and the resistor 56 connected to the secondary side of this.
．． 66, there is no risk of element destruction due to excessive current flow.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. In FIG. 2, four sets of cascode-connected switch circuits 30, 40, 50, and 60 form a single-phase inverter to convert DC power from the DC power supply 10 into AC power and supply the AC power to the load 20; The cascode connection switch circuit 50 on the positive side of the DC power source IO is supplied with on/off signals from the base drive circuit 52 and the gate drive circuit 53 via the signal isolation circuit 54, and the cascode connection switch circuit 60 on the negative side In the embodiment shown in FIG. Same as the case.

In the second embodiment circuit shown in FIG.
Similarly, a saturable transformer 91 with a center tap is inserted in series at the connection point between the cascode connection switch circuits 50 and 60, and the load 20 is connected to both center taps. ing. The secondary windings of these saturable transformers 81 and 91 have resistors 82 and 9, respectively.
2 (or a reactor can be used instead of a resistor) to short circuit. Due to the high speed switching operation, these center tap saturable transformers 81, 91 can suppress excessive current even if one cascode connected switch circuit is turned on while the other is turned off.

In the example circuit shown in FIG. 1 or FIG. 2, the value of the impedance connected to the secondary winding of the saturable transformer is determined so as not to damage the elements constituting the cascode-connected switch circuit. The transformer may be selected so that a current that can be turned off at a high speed can flow, and at that time, the current that steadily flows through the saturable transformer causes almost no voltage drop.

〔Effect of the invention〕

According to this invention, a bipolar transistor and a MOS
A power converter is formed by bridge-connecting cascode-connected semiconductor switch circuits configured by connecting FETs in series, and alternately turns on two sets of cascode-connected semiconductor switch circuits connected in series to a power supply.・In turning off, one side is turned on while the other is in the turn-off period, thereby forcing current to flow and achieving quick turn-off, and the large current due to the arm short circuit is transferred to these cascode-connected semiconductor switch circuits. Since this can be suppressed by the saturable transformer inserted in series, the performance of a cascode-connected semiconductor switch circuit used for high-frequency switching operation can be fully demonstrated. Furthermore, by adjusting the value of the impedance that short-circuits the secondary winding of this saturable transformer, sufficient current can flow for high-speed switching without the risk of element destruction.
It also has the advantage of being able to freely change its settings so that the voltage drop during steady state can be ignored, making it possible to realize a high-performance power conversion device.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a second embodiment of the invention, and Fig. 3 is a circuit diagram showing an example of a cascode-connected semiconductor switch circuit. be. 2) 30.40.50.60 Cascode connection switch circuit, 3 Bipolar transistor, 4 MO3F
E T , 5 diode, 6 flywheel diode, 7.52.62 base drive circuit, 8.53゜63 gate drive circuit, 10 DC power supply, 20
Load, 31, 41.51.61 Saturable transformer, 54
．． 64 Signal isolation circuit, 65 Inversion element, 36.4
6.56.66, 82.92 Resistance as impedance, 81.91 Center tap saturable transformer.

Claims (1)

[Claims] 1) A cascode connection in which a cascode-connected bipolar transistor and a metal oxide semiconductor field effect transistor are both turned on by applying a firing signal, and are turned off by removing the firing signal to both. Two sets of semiconductor switch circuits are connected in series to a power supply, and both cascode-connected semiconductor switch circuits are alternately turned on and off to extract converted power from the connection point between the two. In the power conversion equipment that
The primary winding of a saturable transformer with its secondary winding impedance shorted is connected separately in series to each cascode-connected semiconductor switch circuit, so that during the turn-off period of one cascode-connected semiconductor switch circuit, the other 1. A power conversion device comprising means for alternately repeating an operation of turning on a cascode-connected semiconductor switch circuit. 2) In the power conversion device according to claim 1, the primary winding having a center tap of a saturable transformer whose secondary winding is short-circuited by impedance is connected in series to both the cascodes. A power conversion device characterized by being inserted in series at a connection point of a semiconductor switch circuit.