Reducing steady-state current distortions in sensorless control strategies by using adaptive test pulses

The motion states of a salient-pole permanent- magnet synchronous machine (PMSM) at standstill or rotating at low speed are often estimated by measuring the responses on high-frequency test signals. In some drives, the rotor position is computed by measuring the current ripples which are generated by supplying the PMSM periodically with high-frequency voltage test pulses. Besides these ripples, undesired distortions in the steady-state current have been measured. Simulation results have revealed that these distortions are caused by deviations of the steady-state voltage during the test periods. In this paper, a sensorless strategy is discussed where a strong reduction of the aforementioned steady-state distortions is obtained by adapting the test pulses to the steady-state voltage vector. As voltage measurements are often avoided, an estimation of the steady- state voltage is used which is given by the current controller output. The computation of the adaptive test pulses is done taking into account the voltage restriction of the dc-bus voltage. Simulation results as well as experimental measurements indicate the effectiveness of the enhanced test pulses in a sensorless controlled interior PMSM.