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Pulse width modulation (PWM) converters generate switching common-mode voltages (CMV) across the load terminals. These voltages cause common mode currents, leading to bearing failure in motor loads and electromagnetic interference problems. This study proposes a novel space vector PWM strategy to reduce the CMV in the dual three-phase permanent magnet synchronous motor (PMSM) driven by two-level six-phase inverter. The novel space vector PWM algorithm discards the use of zero vectors. Firstly, the two largest voltage vectors of each sector are selected as main vectors to synthesise reference vector. Then, three groups voltage vector, which are opposite to the main vectors, have been selected as auxiliary vectors. Appropriate auxiliary vector selected is based on the length of zero voltage vector working time. Next, zero vector working time is distributed to the main and selected auxiliary vectors based on voltage-second principle. In addition, CMV and the harmonic component in z1z2 subspace of the proposed space vector PWM are analysed in detail. Finally, the expected CMV reduction to one-sixth of DC voltage and change rate of CMV in each cycle promised by the proposed novel space vector PWM are demonstrated with simulation and experimental results.

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Permanent magnet synchronous motor (PMSM) shows the great potential for use in direct drive system because of its excellent low‐speed direct‐drive capability. However, it suffers from the adverse effect of the cogging torque in comparison with the asynchronous motor. Therefore, reducing the cogging torque, especially the external‐rotor PMSM (ERPMSM) for belt conveyor application, is necessary for enhancing the stable operation and precise positioning performances of the belt conveyor.Herein, a novel tangential magnetization low‐speed high‐torque ERPMSM is proposed and analysed. Furthermore, the expression of the cogging torque of the proposed ERPMSM is derived by energy method. Based on the special structure of the ERPMSM, a new method for cogging torque reduction is introduced. The comparative FEA results for four ERPMSM models are presented to verify the accuracy and effectiveness of this method. The accuracy of the cogging torque FEA results is confirmed by a prototype. Finally, the influence of this method on ERPMSM performance is also analysed carefully in this paper.

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