High-speed Permanent Magnet Synchronous Motor Loss Analysis And Temperature Field Calculation

Permanent magnet synchronous motor (PMSM) is a good choice for high-speed operation due to the high efficiency, simple structure, high power factor and excellent control performance. PMSM is used widely in many applications such as mechanical process, tooling machines, flywheel applications, high-speed centrifuges, high-speed compressors, and so on. Accurately calculate the winding AC loss, stator core loss and rotor eddy current loss are key problems of high-speed PMSM and hot topics of academe. The research mainly focuses on high frequency loss and thermal problem which contains: analytical and numerical calculation of high frequency winding copper loss, core loss, rotor eddy current loss and related experiments; analysis of the influence of drive mode and the rotor position detection error on PMSM loss and construction of high-speed PMSM third-harmonic sensorless control experiment platform; electromagnetic field and temperature field two-way coupled calculation of high-speed PMSM.This dissertation analyses winding skin effect and proximity effect caused by high frequency current deeply. The effects on high-speed PMSM winding AC loss due to inverter PWM current harmonic are studied and the curve of AC/DC loss ratio with PWM carrier ratio is described. The change rule of winding AC loss with motor slot width and slot height variation is analyzed. Through the analysis of influence on AC and DC loss by conductor diameter, get conclusion that there is a minimum value of conductor total loss which changed with diameter in certain current frequency and amplitude. The method adopts multi-strands to reduce the high frequency AC loss in conditions of maintain total area of the conductor constant is researched. Keeping the conductor total area equal, different strands number winding has different critical frequency, multi-strands winding AC loss is smaller than single conductor winding AC loss when below the critical frequency, but above the critical frequency multi-strands winding AC loss is larger. The experiments about the impact of PWM harmonic current and multi-strands on the winding high frequency AC loss are studied and the results proved the correctness of finite element method.Focus on high frequency for high-speed motor and the traditional core loss model which need to measure high frequency loss curves or just estimates loss coefficient by experience, proposes a variable loss coefficient orthogonal decomposition core loss model which comprehensive consideration of motor rotation magnetization and high frequency skin effect. The model can be fitted correlation loss coefficient just through silicon steel loss curves measured on low frequency alternating magnetizing mode by factory and particularly suitable for high-speed motor core loss calculation. Experiments show that the proposed model has a high accuracy both in low frequencies and high frequencies. The improved model is employed to analyze the effects of current harmonic due to PWM chopping, magnetizing direction, the beveling angle of magnets and temperature on stator core loss of high-speed PMSM.A PMSM rotor eddy current loss analytical calculation model which considers the effects of motor airgap, retaining sleeve, eddy current armature reaction field and limited length is established based on the equivalent current sheet. The rotor eddy current loss that caused by stator harmonic current is analyzed through the proposed analytical calculation model. The rotor eddy current loss are also studied by time-stepping FEM and the effects of inverter harmonic current, stator slot-opening, airgap length, retaining sleeve material and thickness on the rotor eddy current loss is researched in depth. The loss separation experiment proves that the analytical method and FEM results are correct.PMSM can be divided into square wave drive PMSM (BLDCM) and sine wave drive PMSM (BLACM). The current waveforms of BLDCM and BLACM are different, so the motor performance and loss are also different. The loss of BLDCM and BLACM is comparative studied by Finite element method and experimental method. The results show that the BLDCM loss is larger than BLACM loss, and the difference become greater with the speed increasing. The influences of rotor position detection error on the high-speed PMSM loss are analyzed in detail and Points out that rotor position detection error impact on high-speed PMSM loss greatly. For the disadvantages that larger loss on sensorless BLDC mode and difficult to start and poor low speed performance on sensorless BLAC mode, a novel third harmonic sensorless PMSM drive system which combined BLDC mode and BLAC mode is proposed. Rotor position detection error of third harmonic sensorless method is studied by theory and experiment. The first-order hold method is used to extend the accuracy of rotor position estimation and improve the system dynamic and static performance.Through the study on NdFeB material temperature sensitivity and the impact of temperature on winding copper loss, stator core loss and rotor eddy current loss under constant current control and constant torque control, points out that it is necessary to realize electromagnetic field and temperature field two-way coupled calculation for accurate calculation of PMSM performance and the temperature rise of parts. A high-speed PMSM 3D transient temperature field model is established. Iterative method is used to achieve electromagnetic field and temperature field two-way coupling and components temperature rise of high-speed PMSM under constant torque control is calculated. The experiments show that the iterative two-way coupling method results closer to experimental values than the traditional one-way coupling results.