JPS5976169A - Current balancing system for parallel connection thyristors - Google Patents

Abstract

PURPOSE:To balance the current shares among a plurality of thyristors to be fired in parallel connection by connecting reactors in series with the respective thyristors and connecting a series of an auxiliary thyristor and a condenser in parallel therewith. CONSTITUTION:Branching reactors 4, 5 are connected in series with respective main thyristors 1, 2. An auxiliary thyristor 3 is connected in parallel with a series circuit of the thyristors 1, 2 and the reactors 4, 5 in series with a condenser 6. The half wave of the vibrating current produced due to the firing of the thyristor 3 of the resonance frequency determined by the reactors 4, 5 and the condenser 6 is superposed on the firing currents of the thyristors 1, 2, thereby improving imbalance of the branching current between the thyristors 1 and 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current balancing method in a thyristor in which a plurality of thyristors are connected in parallel and fired simultaneously.

In general, the voltage-current characteristics of semiconductor devices vary widely depending on the semiconductor device, and when multiple semiconductor devices are connected in parallel and operated, it is unlikely that significant inequalities will occur in the magnitude of the current flowing through each device. well known. In particular, when a power thyristor is operated by supplying a normal gate current, the element voltage drop increases once in the small current region, as shown in Figure 1, and then rapidly decreases. However, since there is a tendency for the so-called step voltage characteristic to gradually increase again after that, this step voltage characteristic can be suppressed by increasing the As shown in the figure, multiple thyristors A/, /16 are connected in parallel...
If an element exhibiting a step voltage characteristic is included in the step voltage characteristic, significant unevenness will occur in current sharing when a plurality of thyristors are fired simultaneously based on the step voltage characteristic.

In other words, one thyristor connected in parallel /161°/
As shown in Figure 3, if all of the 16 thyristors have voltage-current characteristics that exhibit a collected voltage, the circuit current can be reduced from zero or near zero by firing those thyristors A/A and A at the same time. As the current increases, a current flows through each thyristor element according to its voltage-current characteristics, and as the circuit current is gradually increased from OA, the voltage drop gradually increases as the current increases. It continues to increase. At this time, since thyristor elements A/, A, and 2 are connected in parallel, the voltage applied to the thyristor element is the same value, so that the voltage drop increases and the set voltage v1 of element A/ , the voltage drop across element A/ exceeds its set voltage and rapidly decreases to the voltage value V, and then gradually increases again.

At this time, the current of element /f6/ increases, but the current of element temperature 2 once decreases and then increases again when the voltage drop exceeds voltage Vb. The current of element AI is the current value 11 shown in the figure.
The voltage drop when it reaches is the voltage value Vc shown in the diagram, and the current of the element at that time becomes the current value ■2 shown in the diagram, so a significantly unequal shunt ratio will occur between the two wires. .

As detailed above, for thyristor circuit devices such as thyristor circuit breakers in DC power circuits in which the circuit current increases from zero after the thyristor is fired, the thyristor risk exhibiting the set voltage characteristics has conventionally been arise.

SUMMARY OF THE INVENTION An object of the present invention is to provide a current balancing method that can balance current sharing in parallel connections even when using thyristors having set voltage characteristics.

That is, one aspect of the present invention is to connect an actor in series to a plurality of thyristors that are to be connected in parallel and to be fired, and to connect a series connection of an auxiliary thyristor and a capacitor in parallel, and to ignite the auxiliary thyristor. The present invention is characterized in that the current sharing between the thyristors connected in parallel is balanced by the following.The present invention will be described in detail below with reference to the drawings.

First, FIG. 4I shows an embodiment of the present invention in which fλ thyristors are fired in parallel. In the illustrated configuration, 1
．． ．． 2 is the main thyristor which is connected in parallel and should be fired at the same time, and 3 to 7 are the main thyristors 1. This is a circuit element added to balance the current flowing through the circuit. That is, llj is a shunt reactor inserted in series with the main thyristors / and J, and 3 is an auxiliary thyristor connected in series with the capacitor 6 and connected in parallel to the series circuit of the main thyristors l, ko and shunt reactors + and j. and 7 connects the capacitor 4 to the polarity shown, that is,
The auxiliary thyristor is an auxiliary charging circuit for charging with opposite polarity. In a device with a bending configuration, the shunt reactor l,! By superimposing the half-wave of the oscillating current generated by the firing of the auxiliary thyristor 30 with the resonant frequency determined by the auxiliary thyristor 30 and the capacitor 6 on the firing current of the main thyristor /, -, the set voltage is applied to the thyristor element whose main circuit current is smaller. A current exceeding the value corresponding to the main thyristor l,
This is intended to improve the non-uniformity of shunt current between λ.

FIG. 3 shows voltage and current waveforms at various parts in the device shown in FIG. 3, which operates as described above. That is, as shown in FIG. 6, the main thyristor λ has voltage-current characteristics at voltage values V1 and V at which the shunt current of the main thyristor l exceeds the step voltage portion.
Even in thyristor 1, since the voltage does not exceed its own set voltage, most of the main circuit current flows through main thyristor 1, resulting in significant unevenness in the shunt currents. Therefore, when a gate signal as shown in the figure is applied to the auxiliary thyristor 3 at the time tO shown in FIG. , main thyristor l.

− flows superimposed on each branch ignition current.

Therefore, if the inductance value of the shunt reactor torque, j, is selected to be suitably the same value, approximately 2 of the oscillating current/current will flow superimposed on the shunt current of the main thyristor l2.2, and the main thyristor l2. Since the circuit current value of the thyristor element increases due to the superposition thereof, the thyristor element operates beyond the set voltage portion of the voltage-current characteristics of the thyristor element. Once the thyristor exceeds its set voltage, it operates stably at a current value determined by its voltage-current characteristics, so the above-mentioned non-uniformity of shunt currents is significantly improved.

That is, in the state before time t shown in Fig. 1, the current of the main thyristor / is 1 value at point a, as shown in the voltage-current characteristics of Fig. 1, and therefore the main thyristor λ
The current is the value shown at point b.

Therefore, when the auxiliary thyristor 3 is fired at time points t and o, the currents in the main thyristors l and - increase and reach the values shown at point b and point 0, respectively, so that the currents in the main thyristor The current also has a value that exceeds the set voltage portion. Therefore, after that, the superimposed oscillating current decreases.
In C, the shunt currents of the main thyristors L and I stably maintain the values shown at points e and f, respectively, so the unevenness of the shunt currents between the main thyristors l1 and 2 is significantly improved. become.

Note that the following system can be adopted as the auxiliary thyristor 30 firing control system. In other words, they can be roughly divided into two methods depending on the firing timing: one is to periodically apply a firing pulse to the auxiliary thyristor 3, and the other is to apply a firing pulse to the auxiliary thyristor 3 only when there is an imbalance in the shunt currents of the main thyristors. Furthermore, for each of the λ methods, which are roughly divided according to the ignition timing, there are methods that constantly generate a ignition pulse as a condition for operating the ignition control circuit, and methods where the load current is applied to a single thyristor. There is a method in which a firing pulse for the auxiliary thyristor is generated only when the allowable current value of the thyristor is exceeded and parallel firing of two thyristors is required.

[Brief explanation of the drawing]

Figure 7 is a characteristic curve diagram showing an example of L voltage and current characteristics of a thyristor, Figure 2 is a circuit diagram showing the configuration of a conventional thyristor parallel firing circuit, and Figure 3 is the operation of the conventional thyristor parallel firing circuit. Figure 5 is a circuit diagram showing a configuration example of a thyristor parallel ignition device according to the present invention, and Figure 5 is a wave diagram showing voltage and current waveforms at various parts thereof.
FIG. 6 is a characteristic curve diagram showing the mode of operation. ! , ko... (main) thyristor, 3... auxiliary thyristor, ge, j... shunt reactor, " 6... capacitor, 7... auxiliary charging circuit. Patent applicant: Fuji Electric Manufacturing Co., Ltd. Figure 5

Claims (1)

[Claims] l) By connecting a reactor in series with each of the plurality of thyristors to be connected in parallel and fired, and connecting a series connection of an auxiliary thyristor and a capacitor in parallel, and igniting the auxiliary thyristor, the thyristors are connected in parallel. A current balancing method for parallel-connected thyristors characterized by balancing the current sharing between the thyristors.