Investigation Of Interior Permanent Magnet Brushless DC Motor Sensorless Drive For Electrical Air-conditioning In Vehicles

In the automotive electrical air-conditioning, the compressor system is usually powered by motors. The permanent magnet brushless DC (BLDC) motor is small, high power density and simple. So it is very suitable for the automotive working conditions. In this paper, a permanent magnet BLDC motor sensorless drive has been studied for air-conditioning compressor.It is important for BLDC motor to detect the rotor positions. In an integrated compressor motor system, the motor is assembled and sealed within the compressor, where the conditions are harsh and the sensor method is not suitable. A sensorless method based on zero crosspoints of back-EMF was studied in this paper. In this method, there is no need to draw out the motor neutral line or rebuild the back-EMF. So it is much simple and stable, compared with the traditional back-EMF detecting solutions.The noise and occasional miss of zero crosspoints are common in zero crosspoints detection. Hence, a correction method was investigated in this paper to check the accuracy of zero crosspoints. For the mistake and miss in the zero crosspoints detection, the mistake screening and missed point compensation method were implemented to enhance the stability of system.Based on the preliminary study of automotive air-conditioning, a low voltage BLDC motor drive for 12V, 24V power supply was designed. For the high voltage areas such as the electric vehicles, 144V and 288V BLDC motor drive were developed. The comparison of the hardware has been investigated, and the stability and reliability of the two drives has been verified experimentally. The experimental results have shown that the design can meet the requirements of the air-conditioning in vehicles and the two drives are compact and reliability.For the requirements of high-speed and high power in the BLDC motor in air-conditioning, the optimization of motor was important in optimizing the whole system. Hence, the optimization in both electromagnetic and structural design was considered in this paper. Electromagnetic analysis focused on the effects of bridge on electromagnetic performance. In the structural analysis, these parts also had serve influence on mechnical stresses. So it is the important part in structural optimization too.The electromagnetic model was created by finite element method first. Three types of IPM rotors were analyzed. They were radial shape, V shape and U shape. The electromagnetic forces were calculated from electromagnetic model. And then those forces were transferred to a structural model for deformation and stresses analysis.Results of the three type rotors have been compared in this paper. The bridge and segment area have great influence on both electromagnetic and structural performance. Hence, more attention has been taken to them. Additionally, methods to optimize the rotor were investigated in this paper. Finally, experiments of radial shape rotor were taken to verify the simulation results. The experimental and simulation results have shown that the effect of electromagnetic forces are benifical to relief the stresses on bridges partly. The V shape and U shape rotor can not only increase the flux but also withstand severer stresses. However, the cost will be high.