Resolution corrected modulation: the practical realisation of ideal PWM waveforms

One extant problem with voltage-sourced PWM inverter drives is the physical, high power, realisation of `ideal´, microprocessor-computed, PWM waveforms. Although there are many sources of waveform corruption in the `realisation´ process, the authors concentrate on problems arising from the resolution/quantisation limitations imposed by the hardware timer used to translate the `ideal´ PWM switching points into a time domain electrical signal. These problems are exacerbated at higher switching frequencies and lower output (fundamental) amplitudes for any given timer accuracy. Resolution corrected modulation (RCM) is a software technique proposed to compensate for the finite timer resolution limitations of practical timers. It involves applying integral vector feedback to any timing errors between the `ideal´ PWM waveform and that physically realisable. The RCM effectively increases the resolution of a given timer by a minimum of 4 to 5 bits, allowing accurate PWM synthesis of waveforms using readily available (microcontroller) timing devices while maintaining a high PWM switching frequency