Analytical Prediction of Optimal Split Ratio for Short-Time Duty PM Brushless DC Motors Considering Winding Thermal Limitation

ABSTRACT

The temperature gradient of high-torque-density short-time duty permanent magnet (PM) brushless DC motors (BLDCM) is large. Increasing the torque will cause the copper loss and the winding temperature to rise rapidly, which will lead to the risk of the winding insulation damage. A split ratio optimization method is proposed to raise the torque considering winding temperature limitation in this paper. The analytical relationship between the torque, the losses and the split ratio is derived. The transient temperature of the winding is calculated analytically based on the expressions of this analytical relationship. The maximum allowable temperature rise of the winding is converted to the optimization constraint. The optimal split ratio is calculated and the maximum torque within the temperature limit range is obtained. The method is verified by finite element (FE) simulation and experimental test. The FE predicted optimal split ratio value is equal to the analytically predicted value. The error between the simulated and calculated torque is less than 5.7%. The maximum error between measured and analytically predicted temperature is 7.2%. The verification results show that the proposed method can accurately calculate the optimal split ratio and maximizes the torque within the winding temperature limitation.

KEYWORDS:

• Brushless DC motors
• Design optimization
• Finite element analysis
• High-torque-density
• Short-time duty
• Thermal limitation

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number 51809218] and supported by the Fundamental Research Funds for the Central Universities [grant number 2452019257].

Notes on contributors

Quanwu Li

Quanwu Li received the BS and PhD degrees in electrical engineering from Northwestern Poly-technical University, Xi’an, China, in 2009 and 2017, respectively. He is currently a lecturer with Northwest A&F University, Yangling, China. His research interests include of electric motors design, electromagnetic thermal integrated motor design, etc. Email: [email protected]

Zili He

Zili He received the BS, MS, and PhD degrees in agricultural soil and water engineering from Northwest A&F University, Yangling, China, in 2000, 2006, and 2012, respectively. In 2000, he joined the Department of Power and Electrical Engineering at Northwest A&F University, where he is currently an Associate Professor. His research interests include electrical control and hydroelectric power generation. Email: [email protected]

Wei Jiang

Wei Jiang received the MS degree in fluid machinery and engineering from Jiangsu University, Zhenjiang, China, in 2010, and received the PhD degree in fluid machinery and engineering from Xi’an Jiaotong University, Xi’an, China, in 2016. He is currently a lecturer with Northwest A&F University, Yangling, China. His research interests include the design of special pumps, numerical simulation of fluid field, etc. Email: [email protected]

Ze Liu

Ze Liu received the BS and PhD degrees in control theory and control engineering from Xi’an Jiaotong University, Xi’an, China, in 2012 and 2017, respectively. He is currently a lecturer with Northwest A&F University, Yangling, China. His research interests include motion control technology, power electronics, etc. Email: [email protected]

Wei Dong

Wei Dong received the PhD degree in energy and power engineering from Northwestern Polytechnical University, Xi’an, China, in 2018. He is currently a lecturer with Northwest A&F University, Yangling, China. His research interests include design and optimization of motor, simulation analysis of multi-physical field, etc.