SU541285A1 - Method of current distribution between thyristors connected in parallel - Google Patents

Description

The invention relates to the field of electrical engineering, in particular to methods for distributing current across parallel-connected thyristors in phase, and can be applied to high-power controlled direct current converters.

There is a method of leveling currents in parallel-connected thyristors in phase using inductive current leveling reactors (current dividers), in which the currents of a large number of parallel-connected thyristors or equalization diodes are compared with the total initial average: current value.

This method complicates the power part of the converter circuit.

There is a known method of current distribution along parallel branches by reducing the variation of the thyristor on-time using one lead thyristor, which, with its anode current through a pulse transformer, turns on all other thyristors. This method does not provide uniform heat load on the thyristors.

There is a method of current distribution between parallel thyristors by varying the moments of supply of control pulses depending on the error signal determined by the imbalance

currents through the thyristors. This method is a prototype of the invention.

The disadvantage of the prototype is that a significant number of parallel thyristors is underused in terms of load capacity, since the number of parallel thyristors is chosen taking into account the requirements of not exceeding the limit value of the p-junction temperature.

loaded thyristor.

In turn, the loading of the thyristor corresponding to the maximum allowable temperature of the pn junction of the thyristor depends on the variations of the technological parameters: thermal resistance, threshold voltages, diaamic resistance, switching time, as well as factors such as different cooling conditions, the effect of mutual induction fields, and oxidized contact surfaces of thyristors, etc.

In the lime method, the scatter of one of the thyristor parameters — the turn-on time — is compensated, and although the reliability of the parallel thyristors increases,

but the loading of each of the parallel-connected thyristors is not optimal. The aim of the invention is to obtain an optimal current load of parallel-connected thyristors, i.e., the maximum utilization of the load capacity of each thyristor, taking into account the above parameters and their spread.

This goal is achieved by the fact that a mismatch signal is obtained by measuring the temperature of each thyristor and comparing it with a given one.

FIG. Figure 1 shows a block diagram of a device enabling the proposed method to be implemented, where 1 is a multiplication unit for controlling single-phase thyristors; 2, 3, 4 — blocks of control pulses delay; 5, 6-block comparison; 7, 8, 9 temperature sensors; 10, 11, 12 - parallel thyristors; 13, 14, 15 - inductive current dividers.

FIG. Figure 2 shows the timing diagrams of the pulse voltages and currents for thyristors 10, 11, 12, which clarify the operation of the device according to the proposed method, where

and 12,, bi4 - pulses at the output of block 1, incoming PA inputs of the corresponding delay blocks;

2, Hz, t / 4 - pulses at the outputs of delay blocks 2, 3, 4;

Ilo, Jlb ti2 - currents flowing through transistors 10, 11, 12.

The signals to the control electrodes of parallel-connected thyristors 10, 11, 12 come from pulse multiplier 1 through the corresponding delay blocks 2, 3, 4. Each of the thyristors 10, 11, 12 is equipped with an individual temperature sensor 7, 8, 9. The delay time of the control the thyristor pulses 11 and 12 are determined by the signals supplied to the delay blocks 3 and 4. From the output of the delay blocks, the signals are compared with the signal from the temperature sensor 7 mounted on the thyristor 10, whose temperature is taken as the set one.

Start impulse control / 2 thyristor

10 (Fig. 2) is delayed with respect to the pulse t / 12 by time. If the thyristor temperature

11 less than the temperature of the thyristor 10, the difference between the signals from the sensor 8 and the sensor 7 at the output of the comparison unit 5 is negative and, affecting the delay unit 3, shifts the pulse f / 3 in the direction of advance relative to the pulse t / 2. This is the average current for the period of the thyristor AND

increases, and the current of the thyristor 10 decreases slightly until the temperature of the thyristors I and 10 is aligned.

If the thyristor 12 temperature is greater than the temperature of the thyristor 10, then the difference in sigpal from the temperature sensor 9 n sensor 7 on the output of the cp block 6 is positive, affecting the delay block 4, shifts the mioule and /, in the direction of lagging period T, the current of the thyristor 12 decreases, and the current of the thyristor 10 slightly increases to that, the temperature of the thyristors 12 and 10 cannot be compared.

Similarly, the alignment of the temperature of the other thyristors occurs, which ultimately leads to the distribution of currents.

The implementation of the invention in thyristor units for powering vacuum arc and plasma electric furnaces will allow reducing the number of installed pipe converters in converters by 10-25%, and also reducing the inductance of current dividers several times or removing them without degrading the operation mode of the thyristors due to thyristor reserves associated with the spread of their parameters (threshold voltages, turn-on time, thermal resistance, etc.).

Claims (2)

1. A method of current distribution between parallel-connected thyristors, which consists in changing the torques of control pulses depending on the error signal, characterized in that, in order to reduce the number of installed thyristors by optimum current loading of each of them, to obtain the error signal measures the temperature of each thyristor and compares it with a given one. 2. The method according to n. 1, characterized in that, in order to simplify it, the temperature of one nanosecond of parallel-connected thyristors is used as the set temperature. (Pus.2