A microprocessor based PWM inverter is implemented by multi-mode control strategy. A uniform sampling technique is used in the low frequency region by computation, whereas the higher frequency region is based on the look up table method.
To realize the full output potential of a PWM waveform, a pure PWM wave is transformed to squarewave by overmodulation.
The generation of subharmonic is avoided by making the switching frequency an integer multiple of the output frequency.
To obtain a wide output frequency range, the ratio between the switching frequency and output frequency is changed when the switching frequency becomes either too high or too low for satisfactory operation.