Adaptive Harmonic Control in PWM Inverters with Fluctuating Input Voltage

New techniques of harmonic reduction and voltage regulation in PWM inverters with fluctuating input voltage are described. A novel selective harmonic reduction technique is also developed for three-phase full-bridge inverters to reduce the number of switchings per output cycle. For keeping the fundamental load voltage at the present value and suppressing the generation of low-order harmonics when the input voltage fluctuates, the conventional sinusoidal reference of the triangulation method is replaced by a quasi-sinewave whose magnitude varies inversely with the input voltage to keep the product of the reference voltage and the input voltage sinusoidal. Harmonic analysis of the W-type modulation and M-type modulation is given to show that the load voltage spectra of the output waveforms generated with the proposed methods are insensitive to the source voltage fluctuation and load variation. Experimental results confirm the theoretical analysis.