Control and Diagnosis of Permanent Magnet Motors

Abstract

Permanent magnet synchronous machines (PMSMs) have been deployed widely in recent years due to their inherent features such as high efficiency and high power density. Thanks to these merits, they are used in various applications including renewable systems, transportation, and automation systems to name a few. Considering the safety, reliability and system efficiency, these systems should be monitored and maintained carefully to avoid accidents or operation losses. Therefore, developing reliable fault diagnosis and post-fault control tools is essential. To design high performance fault diagnosis and post-fault-control algorithms, drive system requires accurate electrical parameter information and highly precise current and voltage feedback measurement. This dissertation presents a comprehensive monitoring and diagnosis techniques for inter-turn short-circuit (ITSC) fault which can accurately estimate short circuit current based on well calculated motor parameters and compensated feedback signals. Inductances are crucial parameters for electric motors. It is essential to obtain accurate electrical parameter information of a permanent magnet synchronous machines (PMSM) for high performance controller and observer design. Due to the saturation of magnetic elements, the inductances of permanent magnet motors change depending on the operating points. To solve this problem, the inductance model is analyzed carefully and an improved absolute inductance estimation is proposed based on high-frequency current signal injection. Secondly, the compensation of feedback current signal in drive system is studied. To obtain highly accurate current signal, sigma delta ADCs (SD-ADCs) are used to improve sensing resolution and signal-to-noise ratio. However, the additional latency caused by the use of digital SINC filters for demodulation becomes remarkable and degrades the performance of dynamic systems. The effects of latency on the system bandwidth and gain/phase are analyzed in detail and a Kalman filter-based latency compensation algorithm and compensation strategies are proposed. In the last of the research, a comprehensive analysis for ITSC online short circuit current estimation is proposed. By analyzing the voltage harmonics caused by ITSC fault under stationary and rotating reference frame, the relationship between voltage harmonics, short circuit current and reference voltage is established. According to this relationship, a harmonic analysis-based online short circuit estimation method is proposed. Then the proposed short circuit estimation technique is adopted for PMSM healthy condition monitoring and post-fault-control algorithm design.