PROGRAMMED PWM TECHNIQUES TO ELIMINATE HARMONICS - A CRITICAL-EVALUATION

Programmed pulsewidth modulators (PWM’s) eliminating several lower-order harmonics generate high-quality output spectra, which in turn results in minimum current ripple, reduced torque pulsations, and thereby satisfying several performance criteria and contributes to overall improved performance. However, several programmed PWM switching patterns to eliminate harmonics in the output spectra of single-phase and three-phase inverters are possible. Each one of these alternatives leads to a specific advantage in single- and three-phase inverters depending on the application. The superiority of the programmed PWM techniques over the conventional carrier-modulated PWM’s is established first. Next, a critical evaluation of the aforementioned programmed PWM schemes on the basis of application for single-and three-phase inverters is provided, thereby providing the framework and guidelines for the selection of the appropriate technique for each application area. Evaluation criteria include harmonic loss factor and total harmonic distortion factors defined at the input and output of the inverter terminals. Finally, a simple low-cost solution for obtaining the required PWM switching points is proposed. Selected results are verified experimentally. © 1990 IEEE