Per-Phase Analysis, Efficient Implementation and Performance Evaluation of a 24-Sector Discontinuous PWM for Split-Phase Induction Motor Drives

Abstract

Space vector-based 24-sector pulse width modulation (PWM) techniques for split-phase induction motor (SPIM) drive offer better performance than the 12-sector PWM methods; however, these methods are complex to implement. This paper analyses a space vector based 24-sector discontinuous PWM from a per-phase perspective. Analysis of three-phase average pole voltages, pertaining to this method, shows that each phase is clamped for a 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> interval in each half cycle, which is divided into three sub-intervals of 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> , 30 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> and 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> , respectively. The common-mode voltage is shown to be related to the fundamental voltage of one of the phases in each sector and to that of different phases in different sectors. This analysis leads to an understanding of the offset voltages to be added to the two sets of three-phase sinusoidal modulating signals for generating the equivalent modulating signals for the two inverters driving the SPIM. Further analysis of the switching sequences suggests appropriate carrier waves for the modulating signals to be compared against. The computationally efficient implementation of the 24-sector discontinuous PWM (DPWM-1), thus developed, is validated on a 6-kW laboratory prototype SPIM drive. Stator flux ripple-based analysis is used to evaluate stator current distortion and rms torque ripple of different PWM techniques. Simulated instantaneous torque ripple and torque harmonic spectra of the different techniques are compared. The proposed method offers lower THD at high speeds and lower switching loss at high power factors than the 24-sector continuous space vector PWM with significantly low computational effort.