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Combination of Transient and Fundamental Wave Excitation for Low and Zero Speed Sensorless Control of Induction Machines

To realize sensorless control of ac machines which is able to work even at zero speed an additional high frequency excitation is necessary. Different schemes have been presented recently, which use a transient excitation caused by switching of the voltage source inverter. As any additional excitation has also impact on the current ripple and the noise emission of a machine investigations have been made to combine the fundamental wave and the transient excitation into one inverter control scheme. In this paper a new flux position estimation algorithm based on phase current derivative to extract the flux position information is presented. This method is working without additional transient excitation of the machine and requires only the fundamental wave excitation using standard pulse width modulation (PWM) or a slightly modified PWM. Furthermore, only the current response in the two active states of the PWM is exploited, to avoid parasitic influences during the zero switching state. Measurement results are presented to validate the applicability of the presented approach.