Physical understanding of high frequency injection method to sensorless drives of an induction machine

This paper presents a physical understanding of a high frequency signal injection method to sensorless drives of an induction machine and proposes a sensorless algorithm based on it for zero or low stator frequency operation. The fluctuating high frequency signal at a synchronously rotating reference frame with the fundamental stator frequency generates an asymmetry of the spatial impedances in an induction machine. The difference of impedances between the flux axis and the quadrature axis at high frequency signal injection on the rotor flux angle is explained by the equivalent circuit equation of the induction machine. And the physical phenomenon due to the injected signal is analyzed and examined by finite element method under various operating conditions. The difference is also verified experimentally on the test motors. An algorithm to estimate the rotor flux angle and the rotor speed utilizing the physical phenomena without any speed transducer is proposed. It contains a scheme extracting the high frequency impedance components related to the rotor flux position. The experimental results clarify the satisfactory operation of the algorithm with heavy load torque at zero stator frequency or zero speed regardless of operation mode-generating or motoring.