Load power angle tracking harmonic-elimination discontinuous PWM strategy for switching loss minimization

A harmonic elimination pulse width modulation (PWM) strategy is proposed to minimize the switching losses by continuously tracking the load power angle and clamping the switches around the peak current regions for three-phase inverters. The proposed harmonic elimination PWM strategy is a two-phase modulation method, as any desired voltage space vector is contributed by two pairs of switches only with one pair of switches always inactivated. If the peak of the load current can be centered in the clamped area (or the clamped angle) where the switches are inactivated, then switching losses can be minimized. However, during operation, the power angle between the load voltage and current varies with loads. The peak of the load current may not always be centered in the clamped area. By measuring the load power angle on-line, the proposed PWM strategy adjusts the clamped angle so as to center the peak of the load current in the clamped area. To verify the proposed method, a separately excited synchronous motor served as the load, since its current can be arbitrarily controlled to be leading or lagging. Experiments have shown the effectiveness of the proposed approach in tracking the lower power angle variation and in minimizing switching losses.