A New ?-MRAS Method for Motor Speed Estimation

This paper introduces a new method to estimate the motor speed based on the Model Reference Adaptive System (MRAS) technique. The novelty of the proposed MRAS control structure relies on using the motor input impedance angle as a reference state variable to estimate the motor speed. In this context, the reference angle is obtained from measuring the angle between the motor terminal voltage and current vectors using a double-structure Phase Locked Loop (PLL). The tunable angle is instantaneously calculated using the per-phase motor equivalent circuit. Having the impedance angle as the only candidate for the proposed scheme inherently decouples the reference and the adaptive models. This decoupling resulted in obtaining a superior performance at low, high, and zero speeds. The simplicity of the reference and the adaptive schemes ease the analysis, design, and implementation. The introduced speed estimation concept is validated under different scenarios of operating conditions.

Index Terms—Model reference adaptive system (MRAS), motor input impedance angle, vector control, sensorless operation.