A Robust Online Encoder Fault Tolerant Control Strategy for IPMSM Drives

A novel encoder fault-tolerant-control (FTC) mechanism for interior permanent magnet synchronous motor (IPMSM) drives is investigated in this paper to ensure the IPMSM continues to operate in the event of an encoder fault. The proposed approach features a chattering-reduced sliding mode observer that replaces the conventional signum function with a smooth hyperbolic tangent function, enhancing the accuracy and robustness of speed and position estimation. In addition, an integral terminal sliding mode (ITSM) control law is adopted for both current and speed control-loops to ensure precise tracking control objective. Eventually, the encoder fault diagnosis is achieved through a residual-based threshold strategy that monitors the deviation between measured and estimated speeds. In the event of a fault, the reconfiguration mechanism chooses the estimated speed as feedback to the speed control-loop so that the overall drive system continues to operate. The closed-loop stability under three phases of drive operation such as non-faulty, transient, and reconfiguration is explicitly analyzed. Experimental results on an IPMSM testbench, including comprehensive comparisons with typical methods demonstrate the effectiveness of proposed FTC strategy under the most possible types of faults such as abrupt, intermittent, and incipient.