Universal control techniques for fault-tolerant multi-phase permanent magnet motor drives

Abstract

In this work, universal approaches are developed for high performance of multi-phase permanent magnet motor drives under fault conditions. Ideally high performance operation under fault conditions is considered as maximum achievable ripple-free output torque with minimum copper loss. First a generalized approach is developed in time-domain to analyze open-circuit faults of PM motors under different stator winding connections. This analysis method provides a good tool for investigation of multi-phase PM motors under open-circuit fault conditions. Then a frequency domain approach is proposed for open-circuit fault tolerance of five-phase PM motors with trapezoidal back EMF waveform. The proposed approach is more suitable for practical implementation since it only uses fundamental and third harmonic current components. Next, short-circuit fault tolerance of multi-phase PM motors is addressed. A global control solution is proposed that covers open-circuit faults as a special case of short-circuit fault. In addition, an iterative learning based technique is proposed to reduce dependency of the fault-tolerant operation to motor model. Finally, FTC strategies are investigated on direct-drive linear PM motors based on new back EMF model for air-core linear motors. Finite element analysis and experimental results are presented throughout this work to verify proposed control techniques.

There is an increasing interest to move toward more electric drive systems in various applications. Although design requirements are varying, there is no room to make a compromise on safety and reliability of the drive system in aerospace and naval applications. Safe fail approach for fault tolerance is not a valid option and the drive system has to continue operation with acceptable performance even under worst fault conditions. Permanent Magnet (PM) motors offer high efficiency and power density compared to other motor technologies but they do not have inherent fault tolerance capability. Multi-phase design of PM motor drives provides potential for high level of fault tolerance. However, proper fault-tolerant control (FTC) strategies should be developed to provide desired performance for a wide range of possible fault scenarios in multi-phase motor drives.