Design Optimization and Experimental Verification of Permanent Magnet Synchronous Motor Used in Electric Compressors in Electric Vehicles  
[PERSON]  
1 Department of Automotive Engineering, Honam University, 417 Eodeung-daero, Gwangsan-gu, Gwangju 62399, Korea; [EMAIL_ADDRESS]
2  
[PERSON]  
Recently, the PMSM has been used in parts for electric vehicles because it has excellent efficiency characteristics compared with induction motors [5]. PMSM is a structure in which a permanent magnet is embedded in the iron core of the rotor, and the magnetic flux weakening operation area can be widened depending on the difference in inductance of the d-q axis [6]. Because of these advantages, it is widely used in EV or HEV where variable speed operation is required [7]. An electric compressor for air conditioning of electric vehicles has been developed, and by applying high-efficiency PMSM to the compressor, it has the advantage of increasing fuel efficiency regardless of the vehicle's driving speed [8]. Optimal design is essential to meet the various design requirements of PMSM. Optimal design is a method of finding the value of a design variable and obtaining an optimal solution within a limited design area [9]. The previous researches on the optimal design of PMSM can be divided into two categories. First, there are studies using the magnetic equivalent circuits (MEC) model [10,11]. In [10], it was proposed as a study on optimization using MEC model. It has been reported that the MEC optimization method combined with the optimization algorithm can optimize the volume and energy loss of PMSM. In addition, a novel MEC model of PMSM was developed to obtain maximum efficiency, minimum weight and price [11]. However, MEC-based design has a problem in that it is difficult to accurately consider the nonlinearity of parameters. Second, there are studies that combine numerical analysis methods of electrical devices such as finite element analysis (FEA) with optimal design algorithms [12,13]. FEA was performed to take into account the nonlinearity of permanent magnets and electrical steel sheets, which are difficult to consider in MEC. In [12], an optimal design of PMSM based on dynamic characteristics and finite element analysis of PMSM was performed. Design variables that influenced the efficiency characteristics of PMSM were selected and the efficiency and response characteristics were improved through experiments. In [13], the authors announced the optimization design process of PMSM for electric compressors of air conditioners applied to electric vehicles and hybrid vehicles. Research on the optimal design of PMSM using the response surface method has been carried out. In particular, the response surface method is often used in the optimization design of permanent magnet motors. The response surface method typically uses a second order polynomial regression model. However, it is difficult to accurately predict the optimum value because the response surface method becomes highly nonlinear and yields an unstable high-order prediction function. As a similar study related to PMSM, the rated efficiency was improved through the optimum design of 110 W small brushless direct current (BLDC) motor [14]. In addition, a study was conducted to improve the performance of the electric variable valve timing system for improving fuel efficiency and emission of automobiles [15]. Cogging torque is one of the most representative components of torque ripple in PMSM. This phenomenon can be a critical issue to automotive applications that need precision control of the PMSM and are sensitive to noise and vibration. Therefore, recently, studies to improve efficiency and reduce cogging torque have been actively conducted, and mainly focused on reducing the cogging effect by adjusting the combination of pole slot number, pole arc, and core shape [16,17]. Furthermore, the study of [18] performed multi-purpose shape optimization of PMSM based on FEA and particle swarm optimization algorithms.