A Robust Full-Speed Position-Sensorless Control for a Nonsinusoidal Seven-Phase Permanent Magnet Machine

Abstract

This article proposes a full-speed position-sensorless control strategy for a seven-phase permanent magnet (PM) machine with highly nonsinusoidal back electromotive force (EMF), i.e., the first ( $\boldsymbol {E}_{{1}}$ ) and the third ( $\boldsymbol {E}_{{3}}$ ) harmonic EMF are of comparable values, which give more degrees of freedom for the control of the machine. The control is implemented through a vector decomposition of the seven-phase machine into three magnetically independent virtual machines, each of which is controlled in its own rotating frame. The third harmonic EMF can be used here not only for the improvement of the electromagnetic torque but also can be used for the speed/position estimation. An original full-speed range position-sensorless control strategy is proposed by combining a simple and robust I–f control and a slide mode observer (SMO) control. The improved I–f starting method allows a smooth transition from the start-up procedure to an original SMO method control strategy under different load conditions. The SMO control strategy is implemented in the third harmonic rotating frame, which makes the position estimation accuracy improved by 30% at medium- and high-speed ranges. Simulation and experimental results of a seven-phase nonsinusoidal PM machine show the effectiveness of the proposed theoretical analysis.