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Saliency-Based Position Estimation of Permanent-Magnet Synchronous Machines Using Square-Wave Voltage Injection With a Single Current Sensor

This paper presents a saliency-based position sensorless drive of permanent-magnet (PM) machines using a single current sensor for cost-effective applications. For the single current sensor system, the dc-link current is measured for the reconstruction of three-phase currents. The phase current reconstruction can only be realized when active voltages are applied. This limitation results in six immeasurable areas for the current reconstruction using the pulsewidth modulation. In order to implement the saliency-based sensorless drive, a square-wave voltage is injected to minimize the harmonics of reconstructed saliency current for the rotor position estimation. By injecting a square-wave voltage on the direction of the rotor d-axis, the injection voltage vector is nearly perpendicular to the fundamental voltage vector at low speed. The saliency reflected current or the fundamental current can be separately reconstructed by the dc-link current, leading to the reduced reconstruction errors and improved sensorless performance. By using the proposed signal injection technique on a single sensor system, the saliency-based sensorless drive can work on an interior PM machine with a salient ratio of Lq/Ld = 1.35 at 1% rated speed (60/6000 r/min) under full torque load based on the experimental evaluation.