Steady-State Performance of Voltage Source Inverter/Synchronous Machine Drive Systems

The steady-state performance, including harmonic losses and torques, of synchronous machines excited with voltage source inverters is investigated. A frequency-domain solution is presented that uses the Fourier series of the inverter's line-to- neutral voltage and the d-q equivalent circuit for the synchronous machine. The method for calculating the Fourier series of the inverter line-to-neutral voltage only requires the dc link voltage and the switch times for the inverter switching elements. It is shown that a single-frequency harmonic stator voltage causes a harmonic stator current of two frequencies due to the nonsymmetry of a salient pole or nonsalient pole synchronous machine. The analysis has been embodied in a library of Fortran computer programs. Program output includes the Fourier series of inverter output voltage, inverter link current, feedback diode current, Fourier series of stator current, peak stator current, average and peak electromagnetic torque, and I2R losses in the machine windings. Also available are plots of the instantaneous voltages, currents, and electromagnetic torque. Experimental waveforms of a laboratory voltage source inverter/synchronous machine drive system are included for comparison purposes.