PWM DC to AC converter with digital control - uses comparison between an output voltage controlled counter and stored valves to switch carrier to output through thyristor bridge

摘要

The direct input is converted to a fixed, high frequency square wave signal. This is then switched to the output by a controlled rectifier bridge at a time which depends on the mean output voltage required and the carrier waveform during the time interval. The rectifiers switch off when the carrier voltage passes through zero. Stored numerical values corresponding to output levels at successive equal intervals of time are compared with numbers registered by a counter. This is incremented at a frequency proportional to the desired output level, and reset at the start of each input cycle and the controlled rectifiers turned on when the values are equal. The circuit can be used to produce a 1KVA supply at 220V from a 48V dc source with a 16KH3 carrier.