An auto-adjusting PWM waveform generation technique

A digitised strategy is proposed where the required firing angles or switching edge positions for PWM waveform generation are determined by an initial set of verifiable assumptions. A technique is developed, based on a matrix of transcendental equations, to determine the precise angles for minimum harmonic levels. The accuracy of the technique is shown to be dependent on the binary word length used in the microcomputer control process. A second stage in the development is to determine the energy spectra of the PWM waveform by means of Fourier transform analysis. A Fourier transform expression is developed where additional selected harmonics can be detected and eliminated with the use of a software filter. This renders the technique particularly suitable for its inclusion in a microprocessor-based high-speed versatile PWM drive system. The scheme can be shown to be auto-adjusting for harmonic elimination over a wide range of operational conditions