Performance comparison of open-circuit fault-tolerant control strategies for multiphase permanent magnet machines for naval applications

Naval propulsion is facing mutations toward electrification of propulsion system. In naval propulsion applications, motors and drives are required to be highly fault tolerant. For reasons such as reliability, smooth torque and partition of power multiphase motors appears to good candidates for electrical marine propulsion. Permanent magnet machines are preferred over others because of their higher power densities and efficiencies, allowing a more compact and efficient propulsion system design. In this paper, a comparison between two open-circuit fault-tolerant control techniques for 5-phase permanent magnet machines (PMSM) with trapezoidal back EMF is presented. The first technique is an off-line one based on the instantaneous power balance and the Joule losses minimization theory. The second technique is an on-line one based on the minimization of copper losses, as this point appears to be particularly relevant for ship propulsion. The objective of these two techniques is to achieve ripple-free torque with minimum Joule losses. Firstly, the dynamic model of the 5-phase PMSM with trapezoidal back- EMF is given. Then detailed derivation of both control techniques and current reference extraction are presented. Finally, simulation and experimental results on a low-power laboratory test bench are presented and discussed.