Characterizing performance loss and limitations of PMSM operation due to sensorless control for electric compressor application using analytical model
Bowman, Brett R.
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Automotive electric compressors for hybrid and electric vehicle applications, places a heavy importance on the efficiency of the device. Achieving high efficiencies requires the use of high performance permanent magnet synchronous motors, coupled with a high efficiency motor drive and control strategy. The location of the motor restricts the use of shaft position sensors, making the use of sensorless control common for this application. It is understood that sensorless methods are very robust and well developed, however still unable to provide the accuracy that a physical encoder is able to under all scenarios. In this paper an analytical model of a compressor and motor controller system is developed to test sensorless strategies. In order to test the model an existing flux linkage observer from , combined with the active flux method is used to estimate the rotor position. Simulations are performed to test the sensorless control under a variety of speeds and compressor loads. Data from the simulations is used to calculate performance and component losses to isolate the performance reduction due to sensorless control error. The model was able to provide results that highlighted performance weaknesses in the sensorless control strategies. In regards to the flux linkage observer tested, it is determined that the at medium to high speeds the estimated angle from the observer is very accurate and has only a small impact on efficiency. At low speeds the use of sensorless control reduced efficiency by a considerable amount, and also prevented the model from simulating at full load. The controllers performance was also very susceptible to motor parameter variation in the low speed region. Simulations were also were performed in regions of deep flux weakening, to test its impact on the sensorless angle. The implemented observer was not negatively impacted in extended flux weakening region, however the speed loop showed instabilities at very high loads at high torque angles.