2D Temperature Field Analysis And Calculation Of Brushless Doubly-fed Machine Considering Global Region And Different Operating States

Brushless Doubly-Fed Machine（BDFM）has the excellent characteristics such asbrushless structure, high reliability, small capacity of its frequency converter, flexiblemodulation of its power factor and speed. Because BDFM can be used as a motor in ACfrequency conversion adjustable speed drive system or as a generator in variable speedconstant frequency generation system, it has wide applicable potentials. However, theharmonic of in BDFM is large, and the loss and temperature rise are serious, it is lack ofthe study of its temperature field calculation. Based on the Project of State KeyLaboratory of Power Transmission Equipment&System Security and New Technologyof Chongqing University, the thesis focuses on the research of2D temperature fieldcalculation considering global region and different operating states of the BDFM withcage rotor.Firstly, the basic structure, electromagnetic field and harmonic loss calculation of2D time-stepping finite element model coupled with the circuit of BDFM were brieflyintroduced. Then, considering the thermal coupling of air gap, based on the air-gapcoefficient of thermal conductivity method and the air-gap coefficient of heat transfermethod, the BDFM2D global region steady-state and transient temperature fieldcalculation model were established respectively. For different materials, the changing ofthermal conductivity with the temperature of thermal properties and the changing oftransfer coefficient with the cooling wind speed were considered in detail, and themethod of processing the installing micro air-gap between stator core vs. frame wasanalyzed. Thirdly, according to the calculation of the2D global time-varyingelectromagnetic field and steady state and transient temperature field of finite elementby the Ansoft/Maxwell and Ansys Workbench software, the data and variation tendencyof BDFM heat sources and the temperature distribution were obtained. The correctnessof the presented models and the calculated results were verified by the consistency ofthe steady state and transient temperature field calculation results and the temperatureexperimental data of the similar structure of the induction motor. Fourthly, thetemperature distribution considering the various different structures and operating statesof BDFM were obtained. And then the distribution of temperature in BDFM wasdiscussed with the rotor broken bar fault and stator winding interturn short circuit faultcases. The results show that the temperature of BDFM is not evenly distributed with thegrowth of the running time. The maximum temperature is located at the stator controlwinding near the junction box. When the current frequency of control winding keepconstants, the temperature rise will be dropped by increasing the fins height, improvingthe fins shape and wind speed, reducing the load torque and the voltage of controlwinding. The temperature rise is higher at the sub-synchronous operating mode thanthat at the super-synchronous mode with the constant ratio of control winding voltage tofrequency. The temperature rise is reduced significantly at the singly-feed asynchronousoperating mode or at the doubly-fed synchronous operating mode. The temperature riseof the BDFM may significantly increase when rotor broken bar fault or stator windinginterturn short circuit fault occur.The study of this thesis reflects the whole process of2D finite element calculationof electromagnetic field and temperature field in BDFM with cage rotor. Thetemperature distributing regularities of BDFM was revealed. And it is valuable for thesafe operation of BDFM prototype.