A Mid-point inverter for induction machine speed control

Abstract

is connected across the fchyristor. In conduction with opposite polarity and so with forced commutation this device becomes off. In this circuit, although one of the phases is excited at each time, there may be circulating currents at other two phase windings over the commutation capacitors So, the current in the motor phase which is turned off is not interrupted instantaneously. The current waveforms of the phases are both theoretically investigated and experimentally recorded (see sections 2.2.3 and 2.2.4). Before discussion of these findings, the logic circuit of the drive and gate drive circuit will be described. 2.2.2. THE DRIVE CIRCUITRY The drive circuitry can be examined in two sections as logic circuit and gate drive circuit. 2,2.2.1. The Logic Circuit The logic circuit is shown in Figure 2.2. For obtaining clock pulses with varibie frequency, phase- locked loop chip 4046 was used. This chip is a phase- locked loop circuit that consists of a low power, linear voltage controlled oscillator and two different phase comparators with a common signal amplifier and a common comparator input. Here only the linear voltage controlled - 14 -