Strategies for the fault-tolerant current control of a multiphase machine under open phase conditions

Multiphase machines have higher reliability than 3-phase machines. In order to produce smooth torque after one or more phases are open circuit, the stator magnetic motive force (MMF) is kept unchanged. This paper presents fault-tolerant current control strategies of a concentrated winding multiphase machine under open-circuited fault conditions. In a concentrated winding multiphase machine, other current harmonics can be injected to improve the flux distribution as well as torque density. Both phase currents and winding configurations are taken into consideration to keep the harmonics of stator MMF unchanged after the fault occurrence. In the high phase order machine, with Lagrange Method, the remaining phase currents commands are solved when the copper losses are minimized by neglecting some higher-order harmonics of MMF. A detailed discussion and simulation of the strategies are included. FEA simulation results of torque ripple and power loss are presented for the verification of the control methods.