An algorithm for generating optimised PWM for real time micro control applications

In the reported literature so far, microprocessor implementations of optimised PWM for inverter-fed AC drives, are basically memory based. The optimised switching instants are computed off-line, using numerical optimisation methods and stored in the microprocessor read only memory (ROM) as look-up tables. The authors overcome the problem of large memory requirements usually associated with optimised PWM and also allow the switching instants to be computed online in real-time while keeping the harmonics distortion factor at an acceptable low level for three-phase applications. Fundamental voltages comparable to those achieved by the quasi-square wave mode are obtained, hence making it very useful at the upper end of the fundamental PWM voltage range, indeed it is possible to perform V/f control over a wider range. Also since the switching angles are computed online, steady-state as well as transient operating conditions are satisfactorily dealt with