Initial rotor 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 pulse width modulation (PWM) technology. In order to implement the saliency-based sensorless control, 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 rotor d-axis, the injection voltage vector is nearly perpendicular to the fundamental voltage vector. The saliency reflected current or 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 current sensor system, the saliency-based sensorless drive can work on an interior PM machine at the speed of 60-rpm under full torque load based on the experimental evaluation.