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With the deterioration of the natural environment and the scarcity of fossil energy, it is increasingly important to protect the environment, save energy and reduce emissions to achieve sustainable development. The use of motors is increasing in the field of new energy, especially permanent magnet synchronous motors (PMSM), which are widely used due to their slip-ring and brushless structure, low noise level, high output torque and high efficiency (Qiu, 2020). However, due to the presence of cogging torque, permanent magnet motors can have large torque fluctuations during operation, bringing noise and vibration, affecting the motor's operating performance and control accuracy, reducing the life of the motor and increasing costs (Hu et al., 2020). It is particularly important to reduce the cogging torque of PM motors because it is unavoidable.
At present, there has been a great deal of research to find ways to achieve the weakening of slot torque by optimising the structural parameters of different parts of the motor, such as arc coefficient (Wang et al., 2005; Yang et al., 2007), skewed pole (Jeihoon et al., 2016), magnetic pole eccentricity (Song et al., 2004) and stator teeth notching auxiliary slot (Wang et al., 2002). These methods optimised a single structural parameter, which can suppress the cogging torque. However, they also had problems, such as reduced torque density and increased cogging losses. In order to solve the problems caused by the optimisation of a single structural parameter, some scholars have optimised multiple parameters simultaneously, which not only reduces the cogging torque but also improves the performance of the motor to a certain extent. Yao (2023) used a structural combination of different slot widths and unequal-thickness permanent magnets to effectively reduce the cogging torque, but no method was given to determine the optimal combination of slot width and unequal-thickness permanent magnets. Yang et al. (2023) first optimised the symmetry coefficients of the rotor parameters Rib and HRib and then improved the nonuniform air gap, which can effectively reduce the cogging torque of the built-in V-shaped PM motor. In the literature (Ma et al., 2023), the permanent magnets were first segmented, and then the segmented permanent magnets were designed into a diagonal pole structure. Although the weakening of the cogging torque could be achieved, the method was complicated to produce. Feng et al. (2023) proposed a suitable combination of the pole arc coefficient and eccentricity of the permanent magnets to achieve the weakening of the slot torque. Ma et al. (2022) used a suitable combination of the pole arc coefficient of the permanent magnets and different tooth shapes and tooth widths of the stator to optimise the slot torque, and Jia et al. (2013); Deng et al. (2022); Guo et al. (2022) and Wang et al. (2016) proposed the Taguchi method to optimise multiple parameters of the permanent magnet motor to achieve the weakening of the slot torque. Yang et al. (2022) reduced the cogging torque of the built-in V-type permanent magnet motor by combining the uneven air gap structure and magnetic isolation bridge. Zhang et al. (2020) studied the influence of permanent magnet remanence, number of chutes and slot width on cogging torque for permanent magnet motors. Wang et al. (2021) proposed an optimisation method based on embedded magnetic pole offset and uneven air gap eccentric rotor to weaken the cogging torque of double-layer embedded PMSM.