The objective of this paper is to propose two different modified sinusoidal pulse width modulation (SPWM) control schemes, MPWM-S and MPWM-T, for the dc/ac inverter with a non-constant dc voltage source. The amplitude distortion of the pulse width modulated waveforms is caused by the input dc voltage source variation and has the most significant impact on the dc/ac inverter's ac output voltage spectral errors. The proposed MPWM-S and MPWM-T can achieve the desired fundamental amplitude and eliminate the low order harmonic components caused by the dc voltage source variation. The mathematical analysis of the amplitude distortion and the systematic development of the MPWM-S and MPWM-T are presented in this paper. The proposed MPWM-S and MPWM-T are feed-forward compensation methodologies and can be integrated with any practical feedback control schemes. Hardware implementations of the proposed control schemes can be easily accomplished by adding one or two analog multipliers to the traditional SPWM control circuit. The performance of the two proposed modified SPWM control schemes is verified by experimental results.

The proposed analog-based modified PWM control sclheme for the dc-ac inverter can eliminate the low order harmonic components caused by the non-constant dc voltage source. A simple high power factor full bridge rectifier with the valley-fill filter is selected to realize the non-constant dc voltage source Operation modes of the valley 6.U filter are included in the paper. The performance of the proposed modified PWM control scheme is verified by the computer simulation and experimental results.

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