PWM technique for inverter with sinusoidal output current

A sinusoidal pulse-width-modulated (PWM) technique suitable for single-chip microprocessor-based control is described. The proposed scheme can be considered as a digital alternative to the conventional subharmonic method in the sense that online real-time PWM control is possible and synchronization between carrier wave and signal wave is unnecessary. The scheme features a maximum output voltage that is 15% greater than for the subharmonic method, and the number of switchings is 30% less. A description of the PWM pulse-creation principle is given. Most invertor loads have a low-pass filter nature. Taking this into account, a performance function (PF), which is the time-integral function of the inverter output voltage, is introduced. An optimal PWM pattern is obtained by minimizing the distortion factor of the PF. As the calculation of the optimal pattern needs only three multiplications, it can be executed online with a minimum read-only-memory capacity using a conventional microprocessor. The experiment was carried out with an Intel 8096 CPU. The results demonstrate the validity of the proposed scheme.<
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