Design and Control of a New Compound Double-Rotor Electric Machine for Hybrid Propulsion System

In this article, a new compound consequent-pole double-rotor electric machine (CCPDRM) is proposed for hybrid propulsion system application. First, the operating principle and harmonic components in CCPDRMs are elucidated. The winding factor theory for conventional permanent magnet (PM) electric machines is further extended and applied in CCPDRMs. Then, this improved theory is adopted to investigate the structure and winding scheme requirement of the proposed CCPDRMs. In addition, the control strategy for the proposed CCPDRM is established. By utilizing a parameter sweep method, the variation trends of CCPDRMs’ torque density with respect to various geometrical parameters are revealed. Based on this, the structure of CCPDRMs is optimized to acquire a better electromagnetic performance. Next, the proposed CCPDRM is compared with a conventional compound bipolar double-rotor electric machine (CBDRM). It is found that the improved topology has a similar torque density but a much higher PM utilization factor and a lower PM demagnetization risk when compared with the CBDRM. Finally, a prototype is manufactured and tested in different operating modes. Furthermore, various mode-switching processes are performed to emulate the practical driving cycle of hybrid transportation. Both steady-state and dynamic mode-switching experimental results prove the effectiveness of CCPDRMs.