A Seamless Transition Control of Sensorless PMSM Compressor Drives for Improving Efficiency Based on a Dual-Mode Operation

The sinusoidal-wave and square-wave driving modes have been commonly used in permanent-magnet synchronous motor (PMSM) drives for household refrigerator compressors. In general, the sinusoidal-wave drive performs better in some aspects such as torque ripples, a starting performance, and a flux-weakening capability than the square-wave drive. The square-wave drive, however, has the advantage of higher efficiency at low-output-power conditions because of its relatively lower switching loss than the sinusoidal-wave drive. To selectively utilize the benefits of both driving modes, a seamless transition control between the two driving modes is proposed in this paper. Considering that the overall control structure of the sensorless PMSM drive is quite different according to the driving mode, initialization strategies, necessary for a smooth transition, for the pulse-width modulator of the inverter, speed and current controller, and sensorless position/speed estimator are presented. With the proposed method, a dual-mode operation of the sensorless PMSM drive can be achieved without stopping the compressor. The dynamic performance of the proposed transition scheme is tested using simulations and verified by experiments. Experimental result shows that the efficiency of a refrigerator increases up to 2 [%] using the dual-mode operation in comparison with the sinusoidal-wave only drive.