Generalized Formulations and Solving Techniques for Selective Harmonic Elimination PWM Strategy: A Review

Multilevel inverters (MLIs) are widely recommended for DC to AC power conversion as per the load requirements. The MLIs are preferred over other types of multilevel and conventional converters due to their ability to produce staircase output voltage waveforms with superior harmonics profile. However, the performance of MLIs largely depends on the modulation strategy employed. Among the various modulation techniques, the selective harmonic elimination (SHE) method is more efficient in eliminating low-order harmonics from the voltage waveform produced by MLIs. Proper mitigation of the dominant low-order harmonics results in reduction in switching losses in the semiconductor devices and improves the efficiency of the inverter. However, the analytical solution of the nonlinear SHE equations constitutes the main challenge. Over last few decades, various solving algorithms and techniques such as algebraic methods such as resultant theory, numerical techniques and optimization algorithms have been developed and proposed for selective elimination of unwanted harmonics. This review paper presents the various aspects of the problem formulations for SHE technique. Moreover, the detailed principle operation for five different SHE problem-solving techniques is also discussed in this paper. Solution trajectories corresponding to multiple solutions, PWM waveforms with single and multiple transitions at each voltage level and also for pulse-width-amplitude modulation are evaluated and presented to help the researchers gain better insight into the SHE problem and its solution. © 2019, The Institution of Engineers (India).