PULSE WIDTH MODULATION METHOD FOR POWER CONVERTER EQUIPMENT

PROBLEM TO BE SOLVED: To reduce substantial switching loss by performing pulse width modulation by comparing a voltage and a frequency supplied to a load to predetermined values and by stopping the switching of a phase having the largest value of a phase current in a small section. SOLUTION: By considering phase θ of voltage, a process of reversely converting each output voltage Vqe, Vde of rotatory coordinate system to a plurality of phase voltage commands Vas- r, Vbs- r and Vcs- r of stationary coordinate system is performed (ST1). Next, the size of voltage and frequency are judged from each output voltage Vqr, Vde and compared to already set predetermined values (ST2). These predetermined values are reference for performing three-phase pulse modulation or two-phase pulse modulation. If the size of voltage and frequency is smaller than the predetermined values already set, then three-phase pulse width modulation is performed by the higher harmonics of current. That is. three-phase or two-phase pulse width modulation can be performed selectively by the voltage and frequency of a motor, and the switching loss can be reduced.