| Permanent-split-capacitor (PSC) motors are very widely used in fixed-speed and multi-speed configurations, notably HVAC applications. Typical operation using a fixed-frequency supply results in poor motor efficiency and in large torque ripple at twice the electrical frequency. The feasibility of a variable-speed drive to provide stable variable-speed operation, improve steady-state and dynamic torque characteristics, and improve efficiency has commercial interest. Application of existing symmetric variable-speed drive designs to asymmetric PSC motors results in either excessive voltage stress applied to the motor's windings or in insufficient voltage applied to the auxiliary winding resulting in relatively low efficiency and large torque ripple at the motor's design point.;This research identifies key PSC motor characteristics and develops a variable-speed drive to improve operation. The developed variable-speed drive simultaneously reduces the dc bus voltage and increases motor efficiency at rated speed. The dV/dt applied across the motor windings is kept low, and an appropriate magneto-motive force is applied to the motor at all operating points. As a result, the motor and drive system efficiency is increased while preserving reliable motor operation.;The dissertation document presents the proposed topology, detailed modeling, comparative evaluation, simulation results, backed up by experimental evaluation that validate the feasibility of the approach. |
