A Sensorless Drive by Applying Test Pulses Without Affecting the Average-Current Samples

The rotor position of a salient-pole permanent-magnet synchronous machine (PMSM) at standstill or rotating at low speed is often estimated by measuring the responses on high-frequency test signals. In some drives, the rotor position is computed by measuring important current ripples that are generated by supplying the PMSM periodically with high-frequency voltage test pulses. Besides these ripples, undesired distortions in the average-current samples have been measured. Simulation results have revealed that these distortions are caused by a test signal, as it produces a nonzero voltage deviation from the steady-state stator voltage. In this paper, a low-speed sensorless strategy is discussed where a strong reduction of the aforementioned distortions is obtained by adapting the test signals to the steady-state stator voltage. The main assumption is that an accurate estimation of the steady-state voltage is made by using the controller output. The computation of the adaptive test signals is done by taking into account the voltage restriction of the dc-bus voltage. Simulation results, as well as experimental measurements, indicate the effectiveness of the adaptive test signals in a sensorless controlled interior PMSM.