deliver the pulse to control grids G1 and G2. However, the I/O ports of the Panasonic FPX-C30T can generate a pulse with a variable frequency but only a fixed duty cycle or a pulse with a variable duty cycle but a fixed frequency. It is difficult for the PLC to generate a pulse with arbitrarily changing pulsewidths and frequencies. In order to solve this problem, a peripheral circuit based on PLC is designed to obtain the driving pulse required by PIII. Fig. 2 shows the schematic of the circuit. One of the PLC I/O ports delivers a pulse with a duty circle of 20% and an arbitrarily adjustable frequency between 10 and 1000 Hz. This pulse is delayed to generate a new synchronous pulse with a width of 320 μs and subsequently changed into asawtoothwavebyanintegratedcircuit.Thesawtoothwave is leveled by the dc signal from the D/A module of the PLC to produce a square wave as the original driving pulse source. After optical isolation and amplification, the pulse can be used as the driving signal to switch the IGBT. The length and frequency of the pulse can be accurately controlled by the PLC. This system based on PLC can deliver pulses with widths ranging from 10 to 300 μs and frequencies from 10 to 1000 Hz with a maximum duty circle of 1%.