Diagnostic information contained in inter-harmonics of a direct and PWM supplied induction machine

Abstract

The paper contains waveforms of currents for the direct and voltage source inverter supplied induction machine, with account for harmonics and inter-harmonics. By direct supply the grid is assumed to be polluted by 3rd, 5th and 7th harmonics, normally present in real power supply systems. The voltage inverter was assumed to operate in a PWM mode, with perfectly constant DC link current. Spectrums of stator currents for direct supply create reference bases for spectrums by PWM supply. The model of the machine accounts for dependencies of stator and rotor inductances on rotor angle, resulting from winding and air gap geometry. Calculations of the derivatives of inductances, with respect to rotor angle, allowed for calculation of electromagnetic torque and machine's dynamics, with allowance for speed fluctuation, also in steady state operation.