Research On Permanent Magnet Brushless DC Motor Applied In Vehicle Air-Conditioning System

In vehicle electrical air-conditioning systems, the power of compressor is commonly driven by electric motor. Permanent magnet brushless DC motor has the characteristics of small size, high power density, simple structure and etc., thus it is suitable for using in vehicle environment. In this paper, a vehicle air-conditioning compressor system based on a permanent magnet brushless DC motor was designed.In terms of brushless DC motor control system, the detection of rotor position is a critical technique. In the compressor drive system, the motor and compressor used to share a same work space which is rather poor for machines, resulting the restrict of using the position sensor. The position sensorless control method based on back-EMF zero crossing detection which has a key point of detection of the rotor position is studied in the paper. Compared with the traditional back-EMF zero crossing detection method, the terminal voltage detecting method used here need neither lead wire nor fit motor neutral, simple circuit structure, improve the reliability by complex circuits. However, many higher harmonic components are existed in voltage due to the drive switching signal influenced by chopping. Futhermore considering the practical problems of armature reaction, detected electromotive back EMF waveform need to be filtered. A deep first order filter is applied in system next to the detection of back EMF in order to get a high quality of voltage and to assure the subsequent action by the accurate judgement of rotor position. For filter is bound to cause drift of zero crossing, a software method to compensate for the phase shift is introduced in this paper.Through the study of the characteristics of the vehicle air conditioning system, low voltage and high current brushless DC motor driver solution is designed. After comparing of different driven circuit, a stable and reliable one is choosen to simulate in MATLAB/SIMULINK. The results show that the control system designed in this paper can well meet the control requirements of vehicle air-conditioning systems with compact drive structure and reliable operation.