Frequency‐independent rotor position signal generation scheme for a PMBLdc motor without position sensors

Abstract

A simple scheme for generating rotor position signals in a Permanent Magnet Brushless dc Motor (PMBLdcM) without the need for Hall-effect sensors is presented here. In the PMBLdcM, the difference between the terminal voltages reflects the phase back-electromotive force whenever the particular phase is not energised. The line-to-line terminal voltage signals are processed twice to obtain the Position functions or P-functions. The zero-crossing instants of these signals correspond to the instants for energising the individual phases of the PMBLdcM irrespective of the speed. Typically, the position functions are trapezoidal in nature with the magnitude comparable to the applied terminal voltages. Thus, by suitably processing the position functions, the rotor position information similar to the conventional Hall signals can be generated. The proposed technique is simple, easy to implement, frequency-independent, does not require the machine's neutral point and complex mathematical calculations. Moreover, since it involves the processing of real-time signals, the method does not depend upon the accuracy of model parameters. Also, the scheme is effective even at low speeds since the magnitude of position functions is comparable to the applied terminal voltages. The proposed scheme is verified through simulations and experiments for a 1 hp PMBLdcM in the laboratory.