Improved PWM modulation for a permanent-split capacitor motor

This paper first examines and compares several methods for producing a variable speed drive for the permanent split-capacitor (PSC) induction motor. Conventional modulation methods are compared using phasor diagrams and then an improved modulation scheme using a boost converter and a three-phase drive is proposed. The derivation of the required excitation waveforms for any arbitrary PSC machine as a function of the turns ratio is presented in addition to an expression for determining the amount of required DC bus boost. Experimental and theoretical results are included to verify the analysis.