A modified PWM scheme in order to obtain spatial information of ac machines without mechanical sensor

To realise 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 an transient excitation caused by the 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 integrate the fundamental wave and the transient excitation into one inverter control scheme. In this paper a new modified PWM scheme is presented which enables both the fundamental wave excitation to generate the flux and the torque of the machine as well as the transient excitation necessary to obtain sensorless control signals. Simulations as well as measurement results are given to show the advantages and limits of the proposed scheme.