JPS58218866A - Snubber circuit for gate-turnoff thyristor for power - Google Patents

Abstract

PURPOSE:To reduce power loss on switching by adding an auxiliary snubber circuit, which operates only on transient load or the interruption of accident current and power loss thereof can be ignored. CONSTITUTION:A circuit in which a capacitor 11 for snubber and a diode 12 for forming a capacitive current path when the capacitor 11 is charged are connected in series is connected in parallel between the anode and cathode of a GTO10. A resistor 13 for discharging the stored charge of the capacitor 11 for snubber is connected in parallel with the diode 12, and the snubber circuit 14 is formed. The auxiliary snubber circuit 15 is added to the snubber circuit 14. The auxiliary snubber circuit 15 is operated only on transient load or the interruption of accident currents, and the power loss on switching can be ignored.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a snubber circuit for a power thyristor, particularly a gate turn-off thyristor (hereinafter referred to as GTO).

FIG. 1 shows an example of a conventional power GTO snubber circuit.

That is, a snubber circuit is created by connecting a diode 2 (DB) and a capacitor 3 (Cs) in series between the anode and cathode of the GTOl in parallel to the GTOl, and further connecting a resistor 3 (Rs) in parallel to the diode 2. 4.

By the way, when trying to turn off the GTOI by applying a negative bias to the gate, there is inevitably a finite inductance in an actual power switching circuit, and the GTO
The current switching circuit operates at a constant current for a short period of time as long as the anode current falling period of I, that is, for a period of several microseconds or less.

Therefore, as described above, the snubber circuit 4 is added to GTo,1 and it is operated.

In other words, when the gate of GTOI is negatively biased, the impedance between the anode and cathode increases rapidly and the second
As shown in the figure, the anode current iA tends to decrease.

At this time, by adding a capacitive current path composed of a diode 2 and a capacitor 3, the circuit current is transiently transferred from the GTO 1 to the snubber circuit 4 (is). Due to this effect, the current increase rate (di/dt) of the anode voltage applied to the GTOI is suppressed to a value determined by the ratio of the maximum anode current IT to the capacitance of the capacitor C8, that is, "/Cs."

Therefore, the power loss occurring during the falling period (tf) and the subsequent period can be suppressed to a reasonable value, and a large anode current -(iA) can be cut off.

The controllable anode current IT of the GTOI largely depends on the value of the capacitor Cs of the snubber circuit 4, and shows a relationship as shown in FIG. 3, for example.

In an actual device, such as an inverter for motor control, a large current flows when the motor starts, and during constant speed operation,
This results in a significantly lower current flow. In such a case, the capacitance of the snubber capacitor must be selected to a value sufficient to cut off the maximum load current.

For example, in the conventional snubber circuit shown in FIG.
If it is necessary to cut off a current of 600 A at 00 V and maximum load, it can be seen from FIG. 3 that the capacitance of the snubber capacitor cs needs to be 2 μF.

The charge accumulated in this snubber capacitor C8 is mainly consumed in the discharge resistor RS during the next on-period.

Therefore, the switching loss (8) of the snubber circuit is
The value is determined by the formula below.

E = 1 /2 Cs ・VDM2・f [W] −
...'--' (1) In the above formula (1), C8...
・Snubber capacitor, VDM...Maximum load current, f
...Switching frequency of GTO.

However, the above (1) 2K CB ”” 2 μF +
VDM-60OA, lips to substitute f=500Hz・
,9゜E'''/2Cs-Vo
M2・f = 1/2X2XIO'x (6X10")"
x'5xlO-180C infant, i.e. 1st
The addition of the snubber circuit 4 shown in the figure causes a switching loss of isow, which deteriorates the efficiency of the device using the GTO and lowers the upper limit of the practical frequency.

A similar problem also occurs when interrupting load current in the event of an accident.

Conventionally, a snubber capacitor with a large capacity had to be added in order to cut off a large load current during a short period of time when the device was started up or during an accident that rarely occurred, as shown in the above nC. Large switching power losses occur.

However, the load current during steady operation is often about half this low value. For example, in a 600V DC circuit, the breaking current during transients such as -starting or during an accident is 60V.
If it is OA, the snubber capacitor (CS) is
2μF, while the load current during steady operation is 30O
In the case of A, C8 is good (t) O, SμF as shown in Fig. 3.

The present invention has been made based on the above consideration, and is characterized by adding an auxiliary snubber circuit to the conventional snubber circuit, which operates only during transient loads or interruption of fault current, and whose power loss can be ignored. The present invention aims to provide a snubber circuit for a power thyristor, particularly for a GTO.

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

In Fig. 4, a snubber capacitor 11 (C8D) and a diode 12 (Da) for forming a capacitive current path when charging the condenser capacitor C8D are connected in series between the anonide and cathode of GTO10. A snubber capacitor CS is connected to the diode DS.
The accumulated charge discharge resistor 13 (R2O) of a is connected in parallel,
A snubber circuit 14 is formed. An auxiliary snubber circuit 15 according to the present invention is added to this snubber circuit 14.

That is, the auxiliary snubber circuit 15 connects in series a synchronous switching element 16 (,THYs) such as a thyristor or GTO for capacitive current path control added during heavy loads, and an auxiliary snubber capacitor 17 (C3THY). The switching element 16 includes a resistor 18 (R8TII) for discharging the accumulated charge of the auxiliary snubber capacitor C8THY.
Y) and an anti-parallel diode 19 (DTHY) for preventing the auxiliary sensor (capacitor C3TIIY) from being charged through the resistor R81HY during normal operation are connected in parallel.

In the above configuration, as shown in FIG. A current pulse is applied to the gate of element 16.

In addition, after a predetermined energization width has passed during normal operation such as when starting up the device, or in the event of an accident, another detection circuit and G
- After the TO10 gate drive response delay time elapses,
- At time point t''2, the gate of GTOIO is negatively biased to cut off the load current.

In this case, the capacitances of the two snubber capacitors 11 and 17 are adjusted to the above-mentioned load conditions, for example, Cs.

If you choose = 0.5μF + C3THY = 1.5μF, these snubber capacitors can be connected in parallel, so their total capacitance will be 2μF,
It can be seen from FIG. 3 that the force 1 can interrupt an anode current of up to 60 OA.

During steady operation, no current pulse is applied to the gate of the synchronous switching element, so the auxiliary snubber circuit does not work.
Snubber capacitor C3D-0 of one snubber circuit 14
, 5 μF, the switching power loss in the snubber circuit 14 is as follows.

E-1/2C8D-vDM2・f=1/2×0.5×1
0-6×6002×5XlO=45 [W] Note that it is assumed that GTOlo switches at 500 Hz.

However, by adding the auxiliary snubber circuit of the present invention, the switching power loss is reduced by 45% compared to the conventional one.
It can be reduced to 18o-1/4. In addition, a charging current approximately equal to the anode current of the GTO at the time of shutoff flows through the snubber capacitor, and this is repeated at a fairly high frequency, so this capacitor is generally expensive and bulky. circuit'
So, the capacitor that requires the above conditions is C in Figure 4.
8D only, the auxiliary snubber capacitor C3THY may be small and inexpensive because the charging current flows very infrequently.

Therefore, even if the two capacitors used in the circuit of the present invention are combined, both cost and volume can be significantly reduced compared to conventional capacitors.

Moreover, even if the cost and space of newly added synchronous switching elements, diodes, and resistors are considered, it can be sufficiently compensated for.

FIG. 6 shows another embodiment of the present invention, in which an auxiliary sensor circuit is added to the bridge inverter circuit.

In other words, instead of adding the auxiliary snubber circuit 22 to all GTOs such as GTOs 20 and 21, it is necessary to add the auxiliary snubber circuit 22 to either the DC plus ((-) or minus (-) potential (in the figure, the (+) potential side). Added only to GTO20,
Other GTOs 21 and the like have only a conventional snubber circuit 23 added thereto.

In the above embodiment as well, due to the same effect as described above, the switching power loss generated in the snubber circuit can be reduced to a fraction of that of the conventional snubber circuit, and the efficiency of the device is also significantly improved.

In particular, as the number of elements increases, the contribution to reductions in costs, space, etc. increases.

[Brief explanation of the drawing]

FIG. 1 shows an example of a snubber circuit of a power GTO, FIG. 2 is a voltage and current waveform diagram thereof, and FIG. 3 is a diagram showing the relationship between controllable anode current and snubber capacitor capacity.
Fig. 4 is a snubber circuit diagram according to the present invention, Fig. 5 is a waveform diagram of the load current during heavy load, the gate current of the synchronous switching element of the auxiliary snubber circuit, and the gate current of the main GTO. , which shows another embodiment of the present invention, in which an auxiliary snubber circuit is added to the bridge inverter circuit. 10...GTOl 11...Snubber capacitor, 12...° diode, 13...Resistor, 14
... Snubber circuit, 15... Auxiliary snubber circuit,
16...Synchronous switching element, 17...Auxiliary snubber capacitor, 18...Resistor, 19...Diode application agent Patent attorney Kikuchi Gobe Haya l Figure 2 Figure 0 0.5 /, θ
/, 5 2.0 Snubber ■Capacitor C
s[pF] 弗4 @ 45 Figure Haya 6 Figure, 23, 22

Claims (1)

[Claims] 1. In a gate turn-off thyristor with a snubber circuit connected between the anode and cathode, the snubber circuit operates only when a transient load or fault current is cut off, ignoring the switching power loss. A power gate, turn,
Off-thyristor snubber circuit. -2. The auxiliary snubber circuit includes a synchronous switching element connected in parallel to the snubber circuit, an auxiliary snubber capacitor connected in series to this element, and an auxiliary snubber capacitor connected in antiparallel to the switching element, and in a steady state, A power gate turn-off risk snubber circuit according to claim 1, comprising a diode for preventing charging and discharging of a capacitor.