| 摘要 |
PURPOSE:To surely prevent a short circuit between lines, by directly calculating a current flowing period from the ignition phase of a gate and shutting off the gates of a thyristor bridge opposite an operating side. CONSTITUTION:An input to a gate phase shifter 3 and an input V2 applied to another gate phase shifter 4 through a polarity inverter 13 are voltages proportional to an ignition angle alpha. The output VN of a speed detector 12 is proportional to the speed of a DC motor. A subtracter 14 calculates the difference between voltages Valpha, VN. An output Vbeta passed through an amplifier 15 is a voltage proportional to a turn-on angle beta. The polarity of the voltage Vbeta is discriminated. When the voltage Vbeta is positive, an operation inhibiting instruction is applied from a negative side current flowing time calculator 17 to the gate phase shifter 4. When the voltage Vbeta is negative, an operation inhibiting instruction is applied from a positive side current flowing time calculator 16 to the other gate phase shifter 3. As a result, the gates of an opposite side thyristor bridge are not ignitied during a current flowing period to prevent a short circuit between lines. |
