Research On Method Of Electromagnetic Loss Derivation Over The Entire Torque-speed Envelope And Thermal Field In Permanet Magnet Synchronous Motor

As the first candidate of the driving motor for new energy vehicle, the permanent magnet synchronous(PMSM) motor have the characteristics of high power density and high efficiency over a wide range, so that the vehicle can consume the least amount of energy in the whole driving duty cycle. However, due to the strong coupling between electromagnetic and thermal field within the PMSM as well as the real-time variation of working operation of motor, the loss predictions and thermal analysis over the driving duty cycle becomes a great challenge to PMSM for new energy vehicle application. At present, the key to solve the above problem is to map all the loss components over the torque-speed envelope in a timly manner and effectively decouple the internal electromagnetic field and temperature field in the motor design level. This research involves the aspects of derivations of winding loss, iron loss, permanent magntic loss over the entire torque-speed envelope, loss prediction and thermal during the driving duty cycle, which provides theoretical criteria for design and optimization of PMSM for new energy vehicle application.Firstly, calculation formula of AC winding loss in thermal field, which could take temperature factor account, is derived. In order to validate the accuracy of proposed technique, different winding protoypes and their corresponding 2D finite element models are built. Experimental and finite element method are utilized in validation to measure/calculate the value of winding losses. In order to have some insights into the method, the 2D finite element method is used to separate the loss components those come from skin-effect and proximity-effect, then the thermal effect on these two kinds of AC loss components is explained. The method of interpolation is used to derive t Rac/Rdc under different operating frequencies. At last, the winding loss deriving technique over the entire torque-speed envelope which takes temperature correction account is proposed.Secondly, in order to exploit the PM power loss mapping technique which take axial segmentation and temperature correction account, the 2D finite element method is used to illustrate the change tendency of PM power loss with change of quadrature-axis current, direct-axis current and frequency, 3D finite element method is used to illustrate the change tendency of PM power loss with change of number of axial segments and winding end effect. Both 2D FEA and analytical method are utilized to analysis the temperature effect on electrical resistivity and residual of PM material. The proposed loss mapping procedure accounts for the axial segmentation of the PM array through the use of an equivalent electrical resistivity of the segmented PM array, which is obtained from three-dimensional 3D FEA. The PM loss can be accurately mapped across the full operational envelope, including the field-weakened mode, through a single 3D and four twodimensional time-step FEAs. The proposed methodology is validated on both an 18-slot 16-pole and 48-slot 8-pole surfacemounted PMSM designs. The loss mapping procedure results closely agree with the computationally demanding alternative of direct 3D finite-element prediction of the PM power loss undertaken at each of the machine’s operating points. The temperature correction is also validated by 2D FEA.Then, based on existing iron loss calculating equation, the iron loss mapping technique is established, which uses dq current and frequency as input dependent variable. Two temperature correctons, one for lamination and the other for PM, are introduced into the proposed technique to take the temperation effect account. In order to validate the accuracy of the proposed mapping technique, a test bench is set up. And the calculation results closely agree with the experimental results loss undertaken at each of the machine’s operating points.Finally, the lumped parameter thermal method is adopted to build the thermal model of forced water cooling surface-mounted PMSM. The detail of how to build the thermal model is presented. The parameter of potential vehicle is carefully selected and operating points are calculated according to theory of vehicle dynamics. Combining with proposed loss mapping techniques, the variation of loss and temperature distribution of the studied 350 kW PMSM within a UDDs driving duty cycle is predicted. Experiments have been carried out to measure the temperature distribution in a motor prototype. The calculation and experiment results are compared and discussed.