New PWM switching strategy for microprocessor controlled inverter drives

A new high-voltage suboptimal (HVSO) pulse-width modulation (PWM) switching strategy is presented which can be used at high fundamental PWM voltages to achieve a smooth, transient-free, low harmonic distortion, transition from the PWM to quasisquare-wave mode. The design philosophy underlying the development of the new HVSO strategy is aimed at reproducing the special features and desirable characteristics of the optimised PWM strategy, using a simple and efficient microprocessor implementation. The full theoretical development of the new HVSO strategy is presented; and experimental results, from a microprocessor controlled PWM inverter drive, are provided which confirm this theoretical development. It is shown that the new HVSO strategy is superior to all existing PWM strategies, and can be implemented simply and efficiently on a microprocessor controller with only minor modifications to the existing PWM microprocessor implementations. In addition, a new hybrid PWM strategy is proposed and demonstrated, which combines the HVSO strategy with a previously developed suboptimal strategy. It is shown that this new hybrid PWM strategy can be used to cover the complete voltage/frequency range of the drive system up to and including the quasisquare wave mode, with minimised total harmonic distortion.