JPH01283066A - Snubber circuit for gto inverter - Google Patents

Abstract

PURPOSE:To prevent a GTO from being broken by transient vibration. by directly connecting diodes in parallel, etc., to snubber capacitors. CONSTITUTION:A snubber circuit of a GTO inverter is composed of GTO 1U-1X, the arm elements, reactors 2U-2X, feedback diodes 3U-3X, snubbers 4U-4X, a diode circuit 5, a current transformer 6, a diode rectification circuit 7, etc. On this occasion, diodes 43U-43X are connected to each snubber capacitor 41U-41X in parallel. Thus, if the polarity of the snubber capacitor 41X is going to be negative, the voltage level in negative polarity of the snubber capacitor 41X will be clamped to a very small value as the diode 43X gets conducting. As a result, the influence of the GTO 1X is reduced since the vibration phenomenon so far observed is diminished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a snubber circuit for a GTO inverter that suppresses transient oscillating voltage of the GTO, which is an arm element of the inverter.

[Conventional technology]

FIG. 5 is a circuit diagram showing a snubber circuit of a conventional GTO inverter disclosed in, for example, Japanese Patent Application No. 59-158320, in which self-extinguishing switching elements are used as arm elements in a half-bridge configuration. , In the same figure, P and N are the positive and negative poles of the DC power supply, respectively, and 1U and 1X are the gate turn-off thyristors (hereinafter referred to as G), which are arm elements.
(abbreviated as TO), receives on/off signals at its gate so as to alternately turn on/off.

2U and 2X are reactors, connected in series, and G
It is inserted between TOlU and GTO1X.

3U and 3X are feedback diodes, and the feedback diode 3U is connected in anti-parallel to GTOlU, and the feedback diode 3X is connected in anti-parallel to GTOIX.

The snubber 4x includes a snubber capacitor 41X and a snubber diode 42X, and is connected in parallel to GTOlX.

The anode side of the snubber diode 42U of the snubber 4U and the cathode side of the snubber diode 42X of the snubber 4X are connected via a diode circuit 5. This diode circuit 5 is inserted with its cathode side facing the anode side of the snubber diode 42U.

6 is a current transformer inserted into the diode circuit 5;
Both ends 5a and 5b of the next winding are connected to the positive pole P of the DC power supply via diodes 7a and 7b of the diode rectifier circuit 7, respectively, and to the negative pole N of the DC power supply via diodes 7c and 7d.

Next, the operation will be explained. Figure 6(a) and (b)
is a time chart for explaining the operation, and the explanation will be made with reference to this. FIG. 6 (Tu in at,
Tx is the on-period of GTOiU and 1X, respectively, 1w is the load current flowing to the load (L load in this example), and Tu
r IX is the current flowing in GTOiU, 1X, respectively,
Iud and Exd are feedback diodes 3U and 3X, respectively.
, vuc and vXc are the voltages of the snubber capacitors 41U and 41X, respectively, and ID is the voltage of the diode circuit 5.
The current flowing through the current transformer 6 is shown.

Further, FIG. 6Tb) shows an enlarged waveform of the voltage and current of the current transformer 6 when GTOlU is turned off, and vcT is the voltage of the primary winding of the current transformer 60.

Now, at time t1, for example, the GT that has been turned on until now
When the OIU is turned off, the current 1u flowing through the GTOiU is transferred to the snubber 4U, and the snubber capacitor 4U begins to be charged. At this time, the charge of the snubber capacitor 41X of the snubber 4X is divided between the diode circuit 5 - current transformer 6 - snubber diode 42U - reactor 2U - AC output terminal U
The voltage is discharged to a load (not shown), and the discharge is completed at time t2, and the feedback diode 3X begins to conduct.

During this time, the secondary output of the current transformer 60 is converted to the DC power source through the diodes 7a and 7b of the diode rectifier circuit 7, so that a voltage proportional to the voltage of the DC power source is generated between the primary windings of the current transformer 6.

Next, the energy of reactor 2U becomes reactor 2U
- Reactor 2X - Snubber diode 42X - Diode circuit 5 - Current transformer 6 - Snubber diode 42U is fed back to the DC power supply, and the currents of reactor 2U and current transformer 6 are attenuated.

When the iron core of the current transformer 6 undergoes magnetic saturation at time t5, the voltage of the current transformer 6 momentarily generates an overvoltage with the opposite polarity, but the diodes 7b and 7a turn on, reducing the voltage between the terminals 5a and 5b. It works to clamp the DC power supply voltage.

This reverse voltage is the snubber diode 42U - reactor 2U
- Reactor 2X - Snubber diode 42X acts to increase the current in the loop, but since this loop voltage drop is small, the current transformer 6 is reset by the voltage corresponding to this voltage drop, and the reactor 2U and current transformer 6 are reset. The decay time of the current in the device 6 also becomes very long.

When the polarity of the load current is reversed at time t4, the load current flows through the path of the AC output terminal U-reactor 2X-GTO1X.

Here, the operation of the inverter described above is an ideal operation when the wiring inductance can be ignored, but in reality, the wiring inductance cannot be ignored. For example, snubber capacitor 41X - feedback diode 3X - snubber diode 42X If there is a wiring inductance IC in the path, the voltage VXC and current I of the snubber capacitor 41X
When the voltage VXC of the snubber capacitor 41X decreases to zero at time t2 in FIG. 6 (bl), the current of the snubber capacitor 41X suddenly becomes zero, causing damped oscillation as shown by the dotted line waveform.

This vibration frequency is 1/2π 7[, and generally I M
It becomes a high frequency of about H2. Here, ct is the capacitance of the snubber capacitor 41X.

Such a high frequency vibration phenomenon of the snubber capacitor 41X occurs not only in the case of a lagging load as illustrated in FIGS. 6(a) and 6(bl), but also in the case of a leading load. When the GTOIU on the positive arm is turned on while current is flowing to the load side, the GTOIU and reactor 2 are connected from the P side of the DC power supply.
A DC short-circuit current flows in the path of U, reactor 2x, and feedback diode 3X, and when this current becomes larger than the load current flowing through feedback diode 3X, feedback diode 3
x is blocked, the snubber capacitor 41X is charged via the snubber diode 42X, and the GTOI
The snubber capacitor 41U of U is discharged along the path of GTOIU-reactor 2U, 2X-snubber diode 42X-diode circuit 5-current transformer 6.

When this snubber capacitor 41U completes discharging and the voltage of the snubber capacitor 41t) decreases to zero, the current of the snubber capacitor 41U suddenly becomes zero, so the snubber capacitor 41U and GTOIU.

Due to the influence of the wiring inductance of the closed circuit of the snubber diode 42U, a high frequency vibration phenomenon occurs within this closed circuit.

[Problem to be solved by the invention]

Since the snubber circuit of the conventional GTO inverter is configured as described above, electromagnetic noise GTOlU,lX due to high-frequency oscillation phenomena of the voltage and current of the snubber capacitor is generated.
A part of this high-frequency oscillating current is directly shunted to the gate-cathode portion of the GTOIU and IX to fluctuate the gate voltage.
There were problems such as causing GTOIU and IX to malfunction and destroying them.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a snubber circuit for a GTO inverter that can suppress transient high-frequency vibrations of a snubber capacitor and prevent malfunctions of the GTO.

[Means to solve the problem]

The snubber circuit of the GTO inverter according to the present invention can be configured by connecting a diode in parallel to the snubber capacitor or
A diode is connected in antiparallel to the GTO, a diode is connected in series to the anode side of the GTO, or a combination of the two is used.

[For production]

When the diode of this invention is connected in parallel with the snubber capacitor, it acts to reduce the vibration phenomenon and
If a diode is connected anti-parallel to the TO or a diode is connected in series to the anode side, a vibration phenomenon will occur, but this will work to reduce the effect on the GTO, which is the arm element, and by combining these two , to reduce the effects of the two vibration phenomena.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 43U and 43X are diodes, respectively, and are connected in parallel to snubber capacitors 41U and 41X, respectively. Other configurations are the same as in Figure 5,
Components that are the same as those in FIG. 5 are given the same reference numerals, and explanations of the configuration will be omitted.

Next, the operation will be explained. The operation at the time when the polarity of the voltage of the snubber capacitor 41X is reversed at time t2 in FIG. 6 (bl) is as follows.

When the polarity of the snubber capacitor 41X becomes negative,
Since diode 43X conducts, snubber capacitor 4
The 1X negative polarity voltage level is clamped to a very small value. As a result, the conventional vibration phenomenon is reduced, so the influence of the GTOIX, which is the arm element, is reduced.

Note that the capacitance of the diode 43t1.43X needs to have a voltage comparable to that of the GTO, which is the arm element, but the current capacity can be smaller than that of the feedback diodes 3U and 3X and the snubber diodes 42U and 42X. In the example shown in FIG. 6 (bl), care should be taken so that current flows transiently through the diode 43X, and in a steady state, most of the current flows through the feedback diode 3X and the snubber diode 42X.

Further, in this case, a plurality of diodes 43X may be connected in series to improve the above-described shunting during steady state.

Next, a second embodiment of the invention will be described with reference to the drawings. In FIG. 2, 8U and 8X are diodes, which are connected in antiparallel to GTOIU and IX, respectively, and are connected in parallel with feedback diodes 3U and 3X, but the current capacity is that of the feedback diode 3U.

GTOIU directly using something smaller than 3X,
Connect between the anode and cathode of IX.

The rest of the structure is the same as that in FIG. 5, and the same parts as in FIG. 5 are given the same reference numerals.

Figure 6 (During transient vibration of bl, snubber capacitor 41X, feedback diode 3X, snubber diode 42X
Even if vibration occurs in the loop, the reverse voltage is clamped by the diode 8X at both ends of GTOIX, so the influence on GTOIX can be reduced.

In this case as well, it is necessary to take care to divide the current with the diode 8X so that most of the current flows through the feedback diode 3X in a steady state, and a plurality of diodes 8X may be connected in series.

In addition, in large capacity GTO inverters, GTOlU is generally used.
The GTOI
The length of the anti-parallel wiring between U, IX and the feedback diodes 3U, 3X is long (because the diodes gU, 9X
Therefore, it is necessary to shorten the length of the wiring by using a small-capacity stud type structure and connecting directly between the anode and cathode of the GTOIU and IX, respectively.

Next, a third embodiment of the present invention will be described with reference to the drawings. In FIG. 3, diodes 9U and 9X are connected in series to the anode sides of GTOIU and IX, respectively. Generally, a GTO has an anode short emitter structure for high-speed switching, has no reverse blocking ability, and has a structure that allows current to flow from the gate to the anode side. Therefore, when a transient vibration occurs as shown in FIG. 6 (bl), an oscillating current flows through the GTOIX through the cathode-gate-anode path, causing fluctuations in the gate voltage and causing the GTO to malfunction.

In addition, it is known that when a current flows between the gate and anode of GTOIX, the turn-off time of GTO becomes extremely long, so that when GTOlU is turned on next time, a DC short occurs between the anode and gate of GTOIX. In some cases, this may occur. The diodes 9U and 9X have the function of blocking the current flowing between the gate and anode of the GTO as described above, so that fluctuations in the gate voltage do not occur.

Here, the current capacity of the diodes 9U and 9X needs to be equivalent to that of the GTOIU and IX, but since the voltage can be low, the diode 9U
, 9X, the increase in inverter loss caused by the addition is very small.

Note that in the above embodiments, the first to third embodiments shown in FIGS. 1 to 3 above each employ a diode individually; The example diodes may be combined and implemented simultaneously.

Further, in the above embodiment, the diode circuit 5 is connected in series with the current transformer 6, but the above-mentioned patent application No. 59-15
Diode circuit 50 as shown in US Pat. No. 8,320
Alternatively, a self-extinguishing switching element may be connected, and FIG. 4 shows an example in which a self-extinguishing switching element 10 is used in the circuit configuration adopted in the embodiment of FIG. 1. There is.

In FIG. 4, the self-extinguishing switching element is controlled to be turned on in conjunction with the turn-on and turn-off of the arm elements GToltJ and 1X, and is turned off when the snubber energy feedback operation is completed by the current transformer 6. This circuit system is controlled to speed up the reset operation of the current transformer 6, and is suitable for high-frequency switching of inverters.

The operation between times t1 and t3 in FIG. 6 (bl) is similar in this circuit because the self-extinguishing switching element 1o is conductive, and transient vibrations occur. An example is shown in which a GTO is used as an example, but if this GTO does not have a reverse blocking ability, a diode may be added in series with GTOlo (or a diode may be added in series with GTO10). It may also be configured by connecting diodes.

〔Effect of the invention〕

As described above, according to the present invention, a diode is directly connected in parallel to the snubber capacitor, or a G
The structure was configured so that a diode was directly connected in antiparallel to the TO, or a diode was connected in series to the GTO, which is the arm element, or a combination of the two was used. It has the effect of preventing destruction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a snubber circuit of a GTO inverter according to one embodiment of the present invention, and FIGS. 2 to 4 are circuit diagrams showing snubber circuits of a GTO inverter according to other embodiments of the present invention, respectively. Figure 5 is a circuit diagram showing the snubber circuit of a conventional GTO inverter, Figures 6(a) and 6(b).
1 are waveform time charts for explaining the operation of the snubber circuit of the GTO inverter shown in FIG. 5, respectively. IU, IX are GTo, 2U, 2X are reactors, 3U,
3X is a feedback diode, 4U, 4X is a snubber, 41U,
41X is a snubber capacitor, 42U. 42x is a snubber diode, 6 is a current transformer, 7 is a diode rectifier circuit, 5 is a diode circuit, 43U. 43X, 8U, 8X, 9U, 9X are diodes. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Corporation (2 others)
'rt+tz ts

Claims (1)

[Claims] A gate turn-off thyristor is used as an arm element, a reactor is provided in series with at least each arm element on the positive and negative side, and a snubber consisting of a series body of a snubber capacitor and a snubber diode is provided in parallel with each of the positive and negative arms, and the above-mentioned The primary winding of a current transformer is connected in series with a diode or self-extinguishing switching element between the intermediate connection points of each diode and capacitor of both snubbers, and the secondary winding of the current transformer is connected through a rectifier circuit. In the snubber circuit of the GTO inverter that feeds back the energy stored in the snubber to the DC power supply, a diode is connected in parallel to the snubber capacitor, a diode is connected in anti-parallel to the gate turn-off thyristor, or a diode is connected to the gate turn-off thyristor. A snubber circuit for a GTO inverter, characterized by connecting either one of them in series or a combination of two of them.