A novel PWM overmodulation technique with the optimal flat top quasi-sinusoidal modulating wave

A new type of flat top quasi-sinusoidal modulation wave was designed and optimized to solve the complexity issue in the existing pulse width modulation( PWM) overmodulation algorithm. The technique increase fundamental amplitude,at the same time minimizes the low-order harmonic influence. It samples the modulating wave with a triangular carrier wave,and linearly changes PWM fundamental component amplitude through changing the modulating wave height in the linear range. In the overmodulation range,it continuously increases the fundamental component amplitude till approaching a square wave by broadening the flat top width of modulating wave while maintaining the maximum height as a constant. To maintain linearity between fundamental component amplitude and modulation index M in overmoudulation range,a lookup table including the flat top width and M relationship was pre-programmed into a microprocessor for real time implement. The new PWM algorithm is simple. Compared with sinusoidal pulse width modulation( SPWM),the technique produces 19% higher maximum fundamental component amplitude in linear modulation range; its total harmonic current distortion is lower at M∈[0. 55,1],and slightly higher at M∈[0,0. 55]but the increase is less than 2. 2% under the same carrier wave frequency ratio N = 33 condition. The new technique was validated with experiment results.