PM Assisted Synchronous Reluctance Machine (PMA-SynRM) receives increased interests in industry applications. It reduces and the PM usage and offset the torque reduction by employing reluctance torque, achieving comparable performance with lower cost. This type of machine features with low PM flux linkage which is very suitable for fault tolerant application. The machine drive performance and fault-tolerant ability are closely related to their windings. Therefore, this article compares two fault-tolerant motor topology with multiple 3-phase distributed winding and multiple 3-phase concentrated winding.
First, in order to compare and analyze the performance of two types of motors in fair, the two motors should be designed under the same technical specifications, requiring the motor to operate at the rated point with 24 Nm torque at 2000 rpm. For each design sample, simulation calculations are first conducted in Flux, and the relevant data is imported into Hyper Study. Then, Hyper Study uses genetic algorithm to calculate the relevant parameters for the next iteration until the final optimization parameters of the two motors are achieved. Secondly, 2D finite element simulation models of distributed winding motor and centralized winding motor were established using Flux finite element simulation software. The two motors were simulated and analyzed, and the back electromotive force, MTPA curve, output torque, fault behavior and fault tolerance capability under different fault modes are compared and studied. The results show that the efficiency of the concentrated winding motor is 1.1% higher than that of the distributed winding motor. Concentrated winding motor has a lower proportion of reluctance torque and its output torque is 1.2 Nm higher than that of the distributed winding motor when under open circuit condition, but lower than that of the distributed winding motor when under short circuit condition. When under inter turn short circuit, after taking the terminal short circuit(TSC) protection action, the short circuit current of the centralized winding motor is only 80% of that of the distributed winding motor, indicating that the centralized winding motor has stronger fault tolerance performance. Finally, by processing the prototype and building an experimental platform, different load currents are applied to the two motors under healthy operation condition and different fault modes for testing. It was found that the output characteristics and fault tolerance characteristics of the two motors are consistent with the FE simulation results. The experimental results verified the accuracy of the simulation model.
The following conclusions can be drawn: (1) Distributed winding motor rely more on reluctance torque, while centralized winding motor rely more on permanent magnet torque. Centralized winding motor has higher efficiency due to much lower end windings, smaller torque ripple, and better performance. (2) Under open circuit condition, two motors can achieve fault operation through the remaining healthy three-phase windings, and the concentrated winding motor exhibits higher output torque capacity. (3) Under short circuit fault condition, both motors could effectively suppress the short circuit current after TSC, but the distributed winding motor has higher output torque. (4) Under inter turn short circuit fault, after adopting TSC protection action, the inter turn short circuit currents of both motors are significantly weakened, and the fault current of concentrated winding motors is smaller. Fault tolerance performance of the concentrated winding motor for inter turn short circuit is better than that of distributed winding motor. In summary, the two multiple 3-phase PMA-SynRMs are both good candidates for safety critical application. The distributed winding machine is suitable for relatively high speed range while the concentrated winding machine is more suitable for medium and low speed range.
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