JPH078132B2 - Power converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power converter such as a voltage source inverter or a chopper that uses a gate turn-off thyristor.

[Conventional technology]

As is well known, the gate turn-off thyristor does not require commutation rotation, and is therefore widely used in power conversion devices such as voltage source inverters and choppers.

In FIG. 7, a circuit for one phase of the voltage source inverter is shown by a solid line. It should be noted that other one-phase main circuits related to the operation are shown by broken lines. As shown by the solid line, the main circuit for one phase has a pair of gate turn-off thyristors (hereinafter, abbreviated as GTO) 1 and 2 connected in series as DC terminals T ₁ and T ₂ , and the series ends thereof. It is formed by connecting the free-wheeling diodes 5 and 6 to the respective gate turn-off thyristors 1 and 2 in anti-parallel with the connection point as the AC terminal T ₃ . Gate circuits 3 and 4 are connected between the gate and cathode of GTO1 and 2, respectively. GTO1 and 2 are alternately turned on and off by applying a gate current from gate circuits 3 and 4 to GTO1 and 2. It is like this.

The DC ends T ₁ and T ₂ are connected to the DC power supply 16, and the AC end T ₃ is connected to the inductive load 17. The main circuits of the other phases are also formed in the same way, and in order to simplify the illustration, the main parts of the other main circuit for one phase are shown by broken lines in the figure, and the same parts corresponding to the parts of the solid line are designated by the reference numerals. It is shown by adding "'".

As is well known, the voltage source inverter circuit configured as described above turns on GTO1 and 2'at the same time for a certain period, and the
→ GTO1 → load 17 → GTO2 '→ power supply 16
Current in the direction of arrow 18 in the figure, and then for the next certain period GTO1 ′
And 2 are turned on at the same time, power supply 16 → GTO1 '→ load 17 → GTO2
→ It is driven by the path of the power supply 16 so that a current flows in the direction of the arrow 17 in the load 17. As a result, the direct current of the direct current power supply 16 is converted into alternating current and supplied to the load 17.

As is well known, the freewheeling diodes 5 and 6 are
A circuit for returning the electric power stored in the inductive load 17 to the power supply 16 when the TO is turned off is formed. For example, GT
When both O1 and 2'are turned off, the power stored in the load 17 is fed back to the power supply 16 by the circuit of load 17-> freewheeling diode 5 '-> power supply 16-> freewheeling diode 6-> load 17. It Also, in the mode where only GTO1 is turned off and GTO2 'is continuously turned on,
A return current flows due to the circuit of load 17 → GTO2 ′ → freewheeling diode 6 → load 17. Furthermore, resistors 7A and 7B, diodes 8A and 8B, and capacitor 9A for shunting the anode current at turn-off to increase the anode current blocking capability.
A snubber circuit consisting of 9B and 9B is connected in parallel between the anode and the cathode.

On the other hand, the gate circuits 3 and 4 are provided with a resistor 10 and a capacitor 11 connected in parallel between the gate and the cathode, as shown in detail in FIG. 8 as a representative of the gate circuit 4.

The resistor 10 is generally inserted for the purpose of preventing the breakdown voltage between the anode and the cathode from decreasing and increasing the static dv / dt withstand capability.

That is, in general, when the gate-cathode of GTO is opened, the breakdown voltage of the anode-cathode decreases. This is because the leakage current generated when a voltage is applied between the anode and the cathode becomes the gate current. Therefore, a resistor 10 is conventionally inserted for the purpose of bypassing this gate current. As a result, the static dv / dt withstand capability is simultaneously increased.

In this case, the capacitor 11 is effective for further reducing the static dv / dt, and the value of the resistor 10 can be increased by the amount of the static dv / dt absorbed by this capacitor 11, which also has the effect of reducing the gate current consumption. .

[Problems to be Solved by the Invention]

By the way, in such a GTO gate circuit,
It is assumed that TO2 is turned off and a current flows through the freewheeling diode 6 in the direction indicated by the arrow in the solid line in FIG.

At this time, when the GTO2 has a structure in which the NB layer on the anode side is short-circuited to the anode as shown in FIG.・ Because it is equivalent to an NB junction diode, the gate of resistor 10 and emitter short-circuited GTO2
A current as indicated by a broken arrow flows between the anodes. Therefore, carriers are accumulated in the PB / NB junction of GTO2.

In this state, when the short-circuited emitter GTO1 paired with the short-circuited emitter GTO1 is turned on, the freewheeling diode 6 recovers and simultaneously flows through the resistor 10, the gate of the short-emitter GTO2, and the anode. At the same time, the current accumulated in the PB / NB junction is discharged from the gate through the resistor 10. However, since the resistor 10 has the inductance 12 on the actual mounting wiring, an electromotive force is generated in the inductance 12 by the discharged current. Since the polarity of this electromotive force is such that the gate 10 side is positive, a positive voltage V (GK) is generated between the gate and cathode of the short-circuited emitter type GTO2 as shown in FIG. 10 (c). Depending on the value of the voltage V (GK), there is a problem that it acts as a gate signal and the emitter short-circuited GTO2 is erroneously turned on.

At this time, a positive voltage V (AK) as shown in FIG. 10 (a) is being applied between the anode and the cathode of the short-circuited emitter GTO2 by the short-circuited emitter GTO1.

For this reason, the static dv / dt withstand capability of the short-circuited emitter type GTO2 is weakened.Therefore, if the above-mentioned accumulated carriers are superimposed, the short-circuited emitter type GTO2 will turn on incorrectly and the inverter output voltage will become abnormal. There is a problem.

An object of the present invention is to turn off the emitter short-circuited GTO.
However, it is an object of the present invention to provide a power conversion device that can prevent malfunctioning and turn-on of a pair of short-circuited emitter short-circuited GTOs.

[Means for Solving the Problems]

A pair of gate turn-off thyristors connected in series has both ends as a DC end, the series connection point as an AC end, and the gate turn-off thyristor has a main circuit in which a freewheeling diode is connected in antiparallel, respectively. In a power converter in which a resistor is connected between the gate and cathode of the gate turn-off thyristor, an anode-side shortened emitter gate turn-off thyristor is used as the gate turn-off thyristor, and a Schottky barrier diode is inserted and connected in series with the resistor. The power converter is characterized in that the Schottky barrier diode is connected in a direction in which a current flowing from the gate of the anode side emitter short-circuited gate turn-off thyristor to the anode is blocked.

[Action]

In the power conversion device, the emitter short-circuited GTO is turned off, a current flows through the anti-freewheeling diode that is antiparallel, and a current flows from the gate to the anode in the emitter short-circuited GTO to accumulate carriers. In order to prevent this, the Schottky barrier diode is connected in the direction of blocking the current flowing from the gate to the anode, so that the current flowing from the gate to the anode can be blocked. Moreover, since reverse recovery development hardly occurs in the Schottky barrier diode, reverse recovery current hardly flows and carriers are not accumulated in the emitter-shorted GTO.

When the next emitter short-circuited GTO turns on, the displacement current due to the voltage applied to the emitter short-circuited GTO and the accumulated carrier due to the current flowing from the gate to the anode will be superimposed and Short-circuit type
Emitted from the GTO gate. For this, there are no stored carriers because a Schottky barrier diode was used. As a result, the current flowing from the gate to the cathode through the resistor is reduced, and as a result, the voltage drop across the resistor inserted between the gate and the cathode is reduced.

Furthermore, the Schottky barrier diode has an on-voltage of PN.
Since it is lower than the junction diode, it lowers the voltage drop of the resistor mentioned above and also lowers the voltage of the false gate-on signal generated between the gate and the cathode. The problem is solved.

Since the malfunction of the switching element can be prevented in this way, the reliability of the power conversion device is improved.

〔Example〕

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, and the same portions as those in FIG. 7 are represented by the same symbols. In FIG. 1, a point different from the conventional one is that a Schottky barrier diode 13 is connected in series with a parallel circuit of a resistor 10 and a capacitor 11 in a direction of blocking a current between a gate and an anode of a short-circuited emitter type GTO2. As a result, even when the paired short-circuited GTO1 is turned off and the current flows through the freewheeling diode 6, the emitter-shorted type GTO2 passes through the resistor 10 because of the anode-side emitter shorted type. The current flowing between the gate and anode of is blocked. As a result, the positive voltage generated between the gate and the cathode of the short-circuited emitter GTO2 by turning on the short-circuited emitter GTO1 and cutting off the current is blocked by the generation of this positive voltage as described above. The problem that the short-circuited GTO2 is turned on by mistake is solved.

Furthermore, when the short-circuited GTO1 turns on,
Due to the static dv / dt, the displacement current of the short-circuited GTO2 flows from the gate to the cathode through the Schottky barrier diode 13. Since the Schottky barrier diode is used for the displacement current, the accumulated carriers are not superposed. As a result, the voltage drop across the resistor inserted between the gate and cathode is reduced, and since the on-voltage of the Schottky barrier diode is substantially lower than that of the PN junction diode, it is equivalent to the gate-on generated between the gate and cathode. The problem is solved that the voltage drops and the short-circuited GTO2 turns on even though there is no trigger signal.

Fig. 2 (a) shows the current waveform I (FD) of the freewheeling diode 6, Fig. 2 (b) shows the anode-cathode voltage waveform V (AK) of the emitter-shorted GTO2, and Fig. 2 (c) shows the emitter short-circuit. The gate-cathode voltage waveform V (GK) of the GTO2 is shown.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention, in which the diode 13 is connected only in series with the resistor 10 and the capacitor 11 is directly connected between the gate and the cathode of the emitter-shorted GTO2. It is connected.

In this case, the short-circuited emitter short-circuited GTO1 described above is turned on, and the displacement current changes to the emitter short-circuited GT.
Even if it flows to the gate of O2, it is absorbed by the capacitor 11, so
The gate voltage is never positive. However, since the wiring inductance 14 actually exists, it is necessary to make this wiring as short as possible.

FIG. 4 (a) shows the current waveform I (FD) of the freewheeling diode 6 in this embodiment, and FIG. 4 (b) shows the anode-cathode voltage waveform V (A of the emitter-shorted GTO2.
K) and (c) of FIG. 9 show the anode current waveform I (A) of the short-circuited GTO2, and FIG. 8 (d) shows the gate-cathode voltage waveform V (GK) of the short-circuited GTO2. As shown in FIG. 4D, a reverse bias voltage is applied to the gate voltage V (GK) of this embodiment, as is well known. As a result, the second that occurs when GTO1 turns on
Since the level of the gate voltage V (GK) shown in FIG. 6 (c) can be lowered, the false ignition of GTO2 can be prevented more safely. As shown in FIG. 4 (a), when GTO1 is turned off at t ₁ ,
The freewheeling diode 6 is turned on and a feedback current or a return current flows. Freewheeling diode 6
While the current is flowing to VTO, V (AK) of GTO2 becomes a minute voltage corresponding to the forward voltage drop of the freewheeling diode 6. Therefore, even if an ON signal is applied to the gate of GTO2 after turning off GTO1, it does not turn on. Then t ₂
When GTO1 is turned on again, the freewheeling diode 6 is turned off. As a result, since the voltage V (AK) corresponding to the DC power supply voltage is applied between the anode and cathode of GTO2, the displacement current of GTO2 flows to the gate. But first
As in the embodiment shown in the figure, since there are no accumulated carriers in GTO2, the current discharged from the gate of GTO2 is only the displacement current, and the displacement current is absorbed by capacitor 11. As a result, the gate voltage V (GK) due to the displacement current
As shown in FIG. 4 (d), the rising level of GTO2 can be made sufficiently lower than the on level of GTO, so that GTO2 will not be turned on accidentally. Incidentally, the waveform of each part shown in times t ₃ ~t _4, the level of the ON signal of the reverse biased GTO2 gate voltage V (GK), thereby GTO2 are turned on, the anode current I (A) to flow Are shown in association with each other.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention. In this embodiment, in addition to the embodiment shown in FIG. 3, a plurality of diodes 15 are further connected in antiparallel to the diode 13. .

This is because when the current flows through the freewheeling diode 6, the diode 15 prevents the current from flowing through the resistor 10 to the gate and anode of the short-circuited emitter GTO2 due to the ON voltage of the diode 6. Therefore, a plurality of diodes 15 are connected in series according to the ON voltage of the diode 6.

By connecting this diode 15, when the emitter-shorted GTO2 is turned off, the gate and cathode are reverse-biased, and the charge charged in the capacitor 11 is
Is discharged through and drops to the threshold voltage of diode 15. Therefore, when the short-circuited emitter GTO2 is turned on, the current flowing through the capacitor 11 becomes smaller than that in the embodiment of FIG.

FIG. 6 (a) shows the current waveform I (FD) of the freewheeling diode 6 in this embodiment, and FIG. 6 (b) shows the anode-cathode voltage waveform V (A of the emitter-shorted GTO2.
K) and (c) of FIG. 9 show the anode current waveform I (A) of the short-circuited GTO2, and FIG. 8 (d) shows the gate-cathode voltage waveform V (GK) of the short-circuited GTO2. The difference from the operation waveform diagram shown in FIG. 4 is only the level of the reverse bias voltage of the gate voltage V (GK), and the other points are the same, so description thereof will be omitted.

In each of the above embodiments, the gate circuit of the voltage type inverter has been described as an example, but one pair of emitter shorted GTOs are connected in series so that one emitter shorted GTO is turned off while the other is turned on. It can be applied to all power conversion devices having various circuit configurations.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, it is possible to prevent the emitter short-circuited GTO in the off state from being accidentally turned on, and thus there is an effect of significantly improving the reliability of the power conversion device.

[Brief description of drawings]

FIGS. 1, 3 and 5 are circuit diagrams showing first to third embodiments of the present invention, respectively, and FIGS. 2, 4, and 6 are FIGS. 1, 3 and 5, respectively. 5 is a waveform diagram for explaining the operation of FIG. 5, FIG. 7 is a circuit diagram of one phase of a voltage type inverter using a GTO, and FIG. 8 is a conventional gate circuit diagram of one arm of the voltage type inverter. FIG. 9 is a sectional view of the anode side emitter short-circuited GTO, and FIG. 10 is a waveform diagram for explaining the operation of the gate circuit of FIG. 1,2 …… GTO with shorted emitter on the anode side, 3,4 …… Gate circuit, 6 …… Freewheeling diode, 10 …… Resistance, 11
...... Capacitors, 13,15 …… Diodes.

Claims (1)

[Claims] 1. A pair of gate turn-off thyristors (1, 2) connected in series have DC terminals (T ₁ , T ₂ ) at both ends thereof, and the series connection point has an AC terminal (T ₃ ) at the gate turn-off. Each freewheeling diode (5,
6) has a main circuit in which the gate turn-off thyristor has a resistor (1
0) is connected to the power converter, an anode side emitter shortening type gate turn-off thyristor is used for the gate turn-off thyristor, a Schottky barrier diode (13) is inserted and connected in series with the resistor (10),
A power converter in which the polarity of the Schottky barrier diode is connected in a direction in which a current from the gate of the anode-side emitter short-circuited gate turn-off thyristor to the anode is blocked.