Copper loss-minimized remedial control algorithm of fault-tolerant flux-switching permanent-magnet motor

For agricultural motor drive applications, reliability and continuity are very significant, and even under fault condition, continuing the drive operation is essential. Multiphase motors can keep on operating with the remaining healthy phases when open-circuit fault occurs in one or two phases and operating without any other hardware under fault condition. Fault-tolerant flux-switching permanent-magnet (FT-FSPM) motor is a new multiphase stator permanent-magnet fault-tolerant machine which incorporates the merits of high fault-tolerant capability. In this paper, a new remedial control is proposed for a five-phase FT-FSPM motor under open-circuit fault of stator windings to improve efficiency and reliability of the motor drives. Based on the principle of copper loss minimization, the aim of this strategy is to keep output torque unchanged and minimize output torque ripple. A field-circuit co-simulation model is developed and an experimental platform is set up, which are used to evaluate torque performances of 10/19-pole FT-FSPM motor drive under various conditions. Simulated and experimental results will be used for verifying the proposed remedial control method. First, based on the analysis of the structure characteristics of FT-FSPM motor, the fault-tolerant current equations are proposed, in which copper loss is minimized and torque capability is maintained. Second, aiming at the performances of motor current, speed and torque response, the simulation of FT-FSPM motor has been carried out on the basis of Maxwell/Simplorer. In order to assess the normal and faulty operations of the FT-FSPM motor drive, the co-simulation technique is adopted in which the magnetic circuit and the electric circuit are coupled in the time domain, thus providing the convenience of system-level simulation. The modeling tools for the co-simulation are composed of 2 separate packages, namely, the magnetic solver Maxwell 2-D and the circuit solver Simplorer. The magnetic solver performs finite-element analysis (FEA) of the FT-FSPM motor, while the circuit solver performs electric circuit analysis of the power converter. At each time step of co-simulation, the magnetic and circuit solvers exchange the calculated data, and the results produced by one solver will be exported to the other solver in the next step. Consequently, the system performances can be accurately predicted. The simulated results show that the torque can be kept the same as normal and the torque ripple decreases to 13.7% under fault condition when adopting the presented control strategy, while the torque ripple is 33.3% without adopting the strategy. Third, a digital signal processing is used to implement the control for this experiment. A separately excited DC (direct current) generator is used as the variable load. To measure the torque of the proposed motor drive, a transient torque transducer is mounted between the five-phase FT-FSPM machine and the DC generator. Moreover, the currents are sensed by the Hall-effect sensors and the position signal is obtained by the optical encoder with an accuracy of 2048 counts per revolution. It can be found that the torque performance is very good under fault-tolerant condition from the experimental results. Also, it verifies that the FT-FSPM motor drive can successfully perform self-starting capability under the open-circuit fault. From the comparison between simulated and experimental results, it shows that the proposed control strategy can reduce the copper losses, maintain the torque performance and minimize the torque ripple during the open-circuit fault. The correctness and effectiveness of the proposed remedial control strategy are verified. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.