A Generalized Formulation of Quarter-Wave Symmetry SHE-PWM Problems for Multilevel Inverters

A generalized formulation of quarter-wave symmetrical selective harmonic elimination (SHE) problems according to the rising and falling edges of the pulsewidth modulation (PWM) waveforms for multilevel inverters is proposed. The SHE modulation scheme features a broad solution space and can eliminate a large number of low-order harmonics. An effective method for obtaining initial values of switching angles is proposed. This method is based on rules of equal area and superposition of center of gravity (cg) of the PWM section with the sine reference signal. To illustrate the effectiveness of the proposed SHE method, a five-level voltage source inverter with elimination of 11 low-order harmonics is investigated. The SHE-PWM equations that can eliminate harmonics from 5th to 35th with modulation index M varying from 0 to 1.15 are formulated, and solutions are presented. Simulations and experiments based on two sets of solutions are carried out. It is demonstrated that the experimental results agree well with simulated ones, which proves the validity and practicability of the new method proposed.