Model based optimization and fault tolerant control of permanent magnet machines with harmonic injection pulse width modulation

Fault tolerant machines and drives are a key technology in safety critical vehicle power and propulsion applications. This paper presents an optimal torque and speed control strategy for permanent magnet (PM) motors under phase open circuit fault conditions. A per-phase harmonic model of a generic PM machine is utilized to obtain the optimal control signals under faulted conditions. This harmonic model considers the saliency of self inductances and the interaction of harmonic components, which are therefore accounted for the optimization process. Controllability of harmonics is achieved with harmonic injection pulse width modulation (HIPWM). Two versions of optimizations, viz. operation with minimized torque ripple, and a multi-objective optimization which also minimizes copper loss and inverter reactive power transfer, are considered. The speed controller is formulated as a cascaded loop feedback / feedforward system, which facilitates operation even with current sensor fault conditions. The proposed controller is extensively analyzed by means of a finite element model (FEM) based dynamic simulation of a five phase interior permanent magnet machine. Operation under normal and three cases of faulted conditions are presented.