An algebraic algorithm for generating optimal PWM waveforms for AC drives. I. Selected harmonic elimination

The selected harmonic elimination (SHE) pulsewidth modulation (PWM) scheme which eliminates specific lower-order harmonics can generate high-quality output waveforms in PWM inverters. However, its application has been limited since SHE switching angles cannot be calculated online by a microprocessor-implemented modulator. Based on offline optimization, in which multiple SHE solutions were found and analyzed for 3-115 switching angles per quarter cycle, an algebraic algorithm is presented for an ordinary microprocessor to calculate approximate SHE switching angles online with such high resolution that it makes no practical difference between the accurate and the approximate SHE switching angles. A novel control strategy for PWM inverters is proposed, which distinguishes itself by treating the DC link voltage as a variable. It can ideally compensate the DC input fluctuation and eliminate selected harmonics. The proposed control strategy along with the algorithm can be used for AC drives and uninterruptible power supply (UPS) systems to optimize dynamic performance