JPS6185075A - Protecting circuit of thyristor converter - Google Patents

Abstract

PURPOSE:To inexpensively provided a protecting circuit by monitoring the reverse voltage applying period of a thyristor element by using the AC input voltage of a thyristor converter, thereby simplifying a circuit configuration. CONSTITUTION:A power system bus 1 drives through a transformer 2, a thyristor converter 4 and a thyristor inverter 5 a synchronous motor 8. In this case, a voltage transformer 18d as a voltage detector, a reverse voltage application monitor 19 and a gate pulse generator 23 are provided. Thus, when an AC input voltage varies within the prescribed period from a commutation point when a signal is output from the secondary signal generator of the monitor 19 so that the first signal generator outputs a signal, the generator 23 is driven by the AND conditions of the outputs of the both circuits to apply a gate fire signal to the arm of the thyristor converter 4 which is commutated so that the current becomes zero, thereby rectifying it. Thus, it can prevent the thyristor element from damaging due to the partial turning OFF phenomenon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protection circuit for a thyristor conversion device that performs power conversion using thyristors connected in series.

[Conventional technology]

Figure 4 is, for example, Mitsubishi Electric Technical Report VoL, 5 Q, A4.1
976, pp. 226-230, is a conventional thyristor starting device for an electric motor. In the figure, l is the power system bus, 2 is the transformer, and 4 is the thyristor 3&~3f.
6 is a thyristor inverter circuit composed of bridge connections of thyristors 5a to 5f; 7 is a smooth sliding axle;
is a synchronous motor, 9 is a switch, and 10 is a capacitor.

The conventional thyristor starting device is configured as described above, and the three-phase AC voltage of the power system 1 is inputted to the thyristor converter circuit 4 via the transformer 2 and converted to the DC voltage Ea. This DC voltage is supplied to the thyristor inverter circuit 6 via the slip actuator, and further, by the operation of the thyristor inverter circuit 6, an AC input is given to the armature terminal of the synchronous motor 8.

When starting the synchronous motor 8, the high-voltage iris converter circuit 4 enters the power running mode, takes AC electrical energy from the power system 1 side, and supplies DC electrical energy to the thyristor inverter circuit 6 side.

On the other hand, on the thyristor inverter circuit 6 side, this DC electric energy is converted into AC electric energy of a frequency synchronized with the rotation speed of the synchronous electric wall 8, and is supplied to the synchronous motor 8 as rotational energy.

In this way, the synchronous motor 8 gradually increases its rotational speed and is accelerated until it reaches the synchronous speed.

When stopping the synchronous motor 8 that has been accelerated once, the thyristor converter circuit 4 is operated in regeneration mode to convert the inertial energy accumulated in the synchronous motor 8 into electrical energy, which is regenerated while being regenerated to the power system 1. The brakes are used to slow down and stop the vehicle.

When operating the thyristor converter 4 in regeneration mode,
Since the converter normally operates with δ=40 to 60', the voltage applied to the thyristor element of the thyristor converter 4 is as shown in FIG. In Fig. 5, a represents one phase of the line voltage of the AC input voltage (e.g. UV phase), and b represents the arm voltage of one phase of thyristor 7 (e.g. U phase, 4th phase).
(corresponds to the arm voltage in 3a in the figure).

As shown in FIG. 4, when the capacitor 10 is connected within the same main section of the power system, a large voltage distortion occurs in the AC power system 1 when the capacitor 10 is turned on by the switch 9. For example, in FIG. 5a, if we consider the case where the converter 10 is turned on at time T, voltage distortion occurs in the input voltage of the thyristor converter 4, and as a result, the thyristor arm voltage also has voltage distortion as shown in FIG. It appears as distortion. If this distortion is large, as shown in FIG. 5, the voltage oscillations when the capacitor is turned on may cause the voltage to become negative for the period t1, and then temporarily shift to a positive voltage.

When the thyristor converter 4 is connected to a high voltage circuit, the thyristor arm is formed by connecting a plurality of thyristor elements in series.

In this case, in order to turn off all the thyristors connected in series equally, it is necessary to apply a negative voltage to the thyristor elements for a certain period of time (approximately several hundred μs) or more, and the phase control angle r during regenerative operation is The setting is such that a sufficient reverse voltage application period is obtained to turn off the thyristor.

However, when the power system voltage is greatly distorted as in the case where the capacitor 10 is inserted as shown in FIG.
There may be cases where the reverse voltage application period t cannot be secured as a sufficient period for the thyristor to turn off, and due to variations in the characteristics of the thyristor elements, some thyristors turn off during the reverse voltage application period t1 and some thyristors do not turn off. Become.

Therefore, if a positive voltage is applied after the reverse voltage application period t, only some of the thyristors that have been turned off will block this positive voltage, and if the positive voltage application value is large, the device will be destroyed. Then it becomes K.

In order to avoid element destruction due to such partial turn-off phenomenon of series-connected thyristors, conventionally a protection circuit as shown in Fig. 6 was used as shown in 174 ``Pulp Protection Circuit for Insufficient Margin Angle'' of the 1974 Tokyo Branch Conference of the Institute of Electrical Engineers of Japan. I was using it.

In FIG. 6, 174L to 17d are thyristor elements connected in series, 11jL to 11d are resistors, and 12&~1
2d is a light emitting diode, 13a to 13d are optical fibers, 14 is a reverse voltage application period monitoring circuit, 15a to 15d are gate pulse transformers, and 16 is a gate pulse generator.

In the protection circuit configured as described above, the reverse voltage application period t1 to the thyristors 171 to 17d is detected by the light emitting diodes 121L to 12d, and the optical fiber 1
It is input to the reverse voltage application period monitoring circuit 14 via 3&~13d. This reverse voltage application period monitoring circuit 14 monitors the reverse voltage application period tl to each thyristor element.
If the reverse voltage application period becomes shorter than the period required to turn off all thyristor elements, a forced firing signal is immediately given to the gate pulse generator 16, and the gate firing signal is transmitted to each gate pulse transformer 15a to 15d. By applying this to the thyristors 17JL to 17d and igniting all the elements of one arm, destruction of the thyristor elements due to the partial turn-off phenomenon was prevented.

[Problem that the invention seeks to solve]

In the conventional protection circuit as described above, it is necessary to provide a reverse voltage application period monitoring circuit for each of the thyristor elements connected in series, which makes the circuit complicated and expensive. was there.

This invention was made to solve this problem, and is a simple and inexpensive protection circuit that can prevent the destruction of thyristor elements due to the partial turn-off phenomenon of thyristors connected in series by detecting distortion in the power system voltage. The purpose is to obtain.

[Means for solving problems]

The protection circuit according to the present invention includes a voltage detection circuit that detects an AC input voltage to the thyristor converter circuit, a first signal generation circuit that outputs a signal during a reverse voltage application period of the AC input voltage, and each of the thyristor converters. a second signal generating circuit that outputs a signal for a certain period of time from the commutation point when the current in the phase arm becomes zero; and a gate pulse generation circuit that provides a gate firing signal to the arm of the thyristor converter which has undergone commutation where the current becomes zero due to the AND condition of the output of the second signal generation circuit.

[Effect]

In this invention, within a certain period of time from the commutation point at which the second signal generation circuit outputs the signal, the AC input voltage fluctuates and becomes a reverse voltage, and the first signal generation circuit outputs the signal. When it is output, the gate pulse generation circuit is driven by the AND condition of the outputs of both circuits above, and it gives a gate firing signal to the arm of the thyristor converter that has undergone commutation where the current becomes zero, causing it to fire again. , it is possible to prevent destruction of the thyristor element due to the partial turn-off phenomenon.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention), 1-
10 is exactly the same as the conventional device shown in FIG.

18 is a voltage transformer as a voltage detection circuit, 19 is a reverse voltage application period monitoring circuit, and 23 is a gate pulse generation circuit.

FIG. 2 shows a detailed circuit of the reverse voltage application period monitoring circuit 19 described above. In the figure, 18jL to 18C are voltage transformers 18 divided into three phases, 23
3f is the aforementioned gate pulse generation circuit 23 divided into six phases, and the aforementioned reverse voltage application period monitoring circuit 19 is a comparison circuit 201L to 20d as a first signal generation circuit.
, single shot circuit 2 as a second signal generation circuit
15 to 21f, and AND circuits 228 to 22f.

Next, the operation of the above embodiment will be explained with reference to FIGS. 1 to 3. In Fig. 2, the operation of each phase is the same, so U
One phase will be explained. Voltage transformer 18a-2
As shown in FIG. 3a, the UV phase-to-phase voltage on the secondary side of the transformer 2 shown in FIG. 1 appears between the next-side terminals U and O.

On the other hand, as shown in FIG. 3, the thyristor element 3aK of the U-phase arm in the thyristor converter circuit 4 of FIG.
The UV phase-to-phase voltage VUv is not applied during the first 120' interval of the applied voltage, and the problematic period in the reverse voltage application period for turning off the thyristor element is the first 120' interval. Therefore, it is sufficient to monitor the UV phase-to-phase voltage.

Therefore, in the comparator circuit 20 & of the N2 diagram, the reference voltage vref set near the voltage O and the reference voltage vref set near the voltage O in order to monitor the reverse voltage application period of the secondary side voltage vuo of the voltage transformer 18 & which is equal to the UV phase-to-phase voltage are used. vu.

and outputs rHJ as shown in FIG. 3d during the period of Vuo > vref.

On the other hand, when a reverse voltage is applied to the thyristor element 3a,
This is immediately after the thyristor element 3b is ignited and the thyristor element 3a is commutated to zero current, so it is important to check whether the reverse voltage application period necessary for the thyristor element 3a to turn off has been secured. It is sufficient to monitor the period of reverse voltage application of vUv from the time when the commutation from 3a to 3b starts when the gate ignition signal Gpb for ignition is issued.

Therefore, in FIG. 2, a gate firing signal (G, , ) (FIG. 3 C) that fires the thyristor element 3b is input to the single shot circuit 21a, and as shown in FIG. A pulse waveform in which only A is "H" is output.

This period A is set to correspond to a sufficient reverse voltage application period t necessary for turning off the thyristor element 3a.

At time T in FIG. 3a, the capacitor 10 in FIG.
When the voltage is distorted and becomes VUv>Vref at time T, the comparator circuit 20& outputs "H" as shown in FIG. 3d. Under the AND condition with the output of the corresponding single shot circuit 21&, the AND circuit 22a outputs rHJ as shown in FIG. This means that the monitoring period is insufficient and there is a risk of causing the above-mentioned partial turn-off phenomenon. Therefore, the gate pulse generating circuit 23a is driven and the thyristor element 3a is activated at time T as shown in FIG. 3g. A gate firing signal is generated, and then continuous pulses are applied until the gate firing signal (G, b) of FIG. 3C reaches rHJ.

Therefore, the thyristor element 3a is fired again at time T, as shown in FIG. It is possible to prevent destruction of the thyristor element due to partial turn-off phenomenon.

In the above explanation, only the U phase was explained, but the operation is exactly the same for the other phases, only the phase order is changed.

In the above embodiment, a long pulse is used as the gate firing signal of the thyristor element, but a short pulse may be used. Furthermore, although the above embodiments have been described with respect to a starting device for a synchronous motor, the same effects as in the above embodiments can be obtained even in a power conversion device using a three-phase bridge connection such as a DC power transmission system.

Furthermore, even in connection systems other than the three-phase bridge connection, the same effects as in the above embodiment can be obtained, except that the phase of the voltage to be monitored is different.

〔Effect of the invention〕

As described above, according to the present invention, since the reverse voltage application period of the thyristor element is monitored using the AC input voltage of the thyristor converter circuit, the circuit configuration is simple and the thyristor converter is protected. This has the effect of making the abdominal circuit inexpensive.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of an embodiment of the present invention, Fig. 2 is a detailed circuit diagram of the main part of the embodiment, Fig. 3 is a signal waveform diagram showing the operation of this invention, and Fig. 4 is a conventional circuit diagram. A circuit diagram of a starting device for a synchronous motor, Fig. 5 is a signal waveform diagram showing a state in which power supply voltage distortion occurs during operation in regeneration mode and a turn-off phenomenon of g minutes occurs in one phase arm of the thyristor converter circuit, Fig. 6. 1 is a diagram of a power conversion device using a conventional partial turn-off prevention circuit. 18 is a voltage converter circuit (voltage transformer), 20 is a first signal generation circuit (comparison circuit), 21 is a second signal generation circuit (single shot circuit), and 23 is a gate pulse generation circuit. In the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Corporation Figure 5

Claims (1)

[Claims] a voltage detection circuit that detects an AC input voltage to the thyristor converter circuit; a first signal generation circuit that outputs a signal during a reverse voltage application period of the AC input voltage detected by the voltage detection circuit; and each phase of the thyristor converter. a second signal generation circuit that detects a commutation point when the current in the arm becomes zero and outputs a signal for a certain period of time from this commutation point;
and a gate pulse generation circuit that provides a gate firing signal to the arm of the thyristor converter that has undergone commutation such that the current becomes zero due to an AND condition of the output of the signal generation circuit and the second signal generation circuit. Protection circuit for thyristor converter.