On maximizing gain and minimizing switching frequency of delta modulated inverters

It is shown that it is possible to reduce and stabilize the switching frequency of three-phase delta-modulated PWM (pulse-width-modulated) inverters, while improving performance. This has been achieved by exploiting the characteristics of three-phase systems. The proposed modulator is based on controlling only two inverter legs at any given time, and forcing the switches in the other leg to remain permanently on or off for specified time intervals. The scheme imposes no penalty on the transient performance and the quality of the output waveform does not suffer. The resulting voltage gain of the inverter is also increased to the level of optimized techniques. Implementation of the technique is simple, requiring no additional computation or circuits. Experimental results on a 5 kVA unit confirm the feasibility of the proposed modulator