Principle of induction melting furnace: requirements for rectifier trigger circuit

1. For the frequency and phase of the pulse, we use a three-phase bridge-type fully-controlled rectifier circuit, which shares six thyristor components. Therefore, the trigger circuit is required to provide six periodic trigger signals (Vg, Vg2, Vg3, Vg4, Vg5, V g6) And the phase relationship of the six trigger pulses is 60° mutually different in sequence.

2. Pulse width and leading edge: in the analysis of the working principle of the three-phase bridge-type fully-controlled rectifier circuit, it is mentioned that the fully-controlled bridge must have two thyristors turned on at any time, which requires every cycle (360°) Within, there must be and only two pulses exist at any one moment. Therefore, the width of each pulse should be greater than T/60=60°, and the width of the trigger pulse should not be too wide. Generally, it is hoped to be less than T/3/120°. In order to trigger correctly, the trigger pulse is required to have a sufficiently steep leading edge, but because the trigger pulse frequency in the same rectifier system is low (50Hz) and the pulse width is large (greater than T/6), if the thyristor components are not connected in series , The requirement for the leading edge of the trigger pulse is not high, as long as it can be less than 0.3ms.

3. The power of the pulse, in order to enable the thyristor to be turned on under the use of the trigger pulse, the trigger pulse is required to have a certain power. The maximum trigger voltage and the maximum trigger current of the control electrode required by the thyristors of different capacities are different.

For example, the maximum trigger voltage of KP200A is 4V, the maximum trigger current is 200mA, the maximum allowable forward voltage of the control pole is 10V, and the maximum allowable current of the control pole is 2A.

4. Phase shift, in order to enable the rectifier circuit voltage to meet the signal requirements of "current limit", "voltage limit", "overcurrent", "overvoltage", etc., it is required that the phase of the rectifier pulse generated by the trigger pulse can be within "0°～150° ”Within the scope of the change.