Research On Efficiency Optimization Control Of In-wheel Motor Based On Magneto-thermal Coupling

As the most typical driving element of the distributed drive system,the in-wheel motor is called the final driving form of electric vehicles.The In-wheel motor is integrated in the wheel,which is difficult to dissipate heat and the temperature rise is high,which causes the loss of the motor to increase,reducing the efficiency of the motor.High-quality in-wheel motor and its control have become important research directions in the field of electric vehicles.There is a complex multi-physics field coupling system inside the motor.The electromagnetic field interacts with the temperature field.The traditional model-based minimum loss control strategy relies heavily on electromagnetic parameters.It does not fully consider the variation of the electromagnetic parameters inside the motor under the coupled system,and the electromagnetic parameter error is large.Therefore,studying the changing law of electromagnetic parameters in a magnetic-thermal coupling system,improving the parameter estimation accuracy,and improving the traditional model-based minimum loss control strategy can further improve the efficiency of in-wheel motors.First,a electromagnetic-thermal coupling model of an in-wheel motor is established to study the changing law of electromagnetic parameters.The electromagnetic field finite element model of the in-wheel motor and the equivalent thermal network method temperature field model are established.The characteristics of the electromagnetic field and temperature field in the coupled system are studied.The loss and temperature rise performance of the motor are analyzed.Simultaneously,the simulation is verified by the temperature rise experiment of the motor platform.Using magnetic-thermal coupling analysis,the effects of speed,orthogonal axis current,temperature and other factors on the permanent magnet flux linkage,winding resistance,iron loss,and inductance were studied,and the key electromagnetic parameter changes of the motor loss under multiple factors were obtained.Secondly,the traditional model-based minimum loss control strategy is analyzed,and the influence of parameter errors on the control strategy is studied.According to the motor loss model and the motor loss minimization as a condition,a MATLAB/Simulink simulation model of the control system is established,and the control strategy and two different command current calculation forms based on the model loss minimum control strategy are compared and analyzed.The degree of influence of electromagnetic parameters on the control effect of the minimum loss control strategy.The error variation curve of the control accuracy affected by the electromagnetic parameters is obtained.It can be seen that the traditional model-based minimum loss control strategy is affected.Thirdly,the parameter estimation method is studied based on the magnetocaloric coupling.According to the simulation data,the mathematical model of parameters such as permanent magnetic flux linkage,winding resistance,and iron loss resistance is fitted.Considering the difficulty of measuring the temperature of permanent magnets,a method for predicting the temperature of permanent magnets based on the thermal circuit method was proposed.L-M algorithm was used to tune the coefficients.Finally,the calculation method of command current based on the electromagnetic parameter estimation was obtained.In order to verify the feasibility,a processor-in-the-loop experiment was performed on the DSP F28335 platform.Finally,according to the parameter estimation method,the traditional model-based minimum loss control strategy is improved.The control strategy is simulated and analyzed under multiple operating conditions.The improved control strategy has good dynamic performance.The improved control strategy reduces the loss of about 27 W and the efficiency of 2.8% under the conditions of 500 rpm and 20 Nm,and reduces the loss of about 81 W under the conditions of 1000 rpm and 30 Nm,improved the efficiency by 2.6%.