Design On Control System Of Electric Vehicle Air Conditioning Compressor

With the emergence of severe environmental pollution problems caused by the shortage of fossil energy, an inevitable trend is the electric vehicle instead of fuel vehicle. Electric vehicle has the advantages of simple structure, no pollution, low use cost.The performance of compressor, which is the core of the air conditioning system,is highly related to running state of the entire air conditioning system.Compressor in electric vehicle is different with that in fuel vehicle because the former has stricter requirement in size and energy,and thus early mechanical compressor has gradually been replaced by the electromotion compressor. The integration control system of brushless dc motor and compressor system is discussed in this thesis. This article is to focus on temperature control system of vehicle compartment and electromagnetic noise suppression of motor in electromotion compressor used in the control system. The main research work is as follows:The temperature control system of vehicle compartment is designed into a three-loop system,which consists of a temperature loop, speed loop and torque loop.The outer temperature loop is used to control temperature of vehicle compartment;the speed loop is used to control the speed of compressor motor according to the output of temperature controller;torque loop is used to control torque of the compressor motor on the basis of controller output in speed loop.The research of temperature outer loop is under the framework of three-loop temperature control system of vehicle compartment. The amount of deviation which is between comfort temperature set by passenger and vehicle real-time temperature is taken as input of temperature controller and given value of the electromotion compressor speed is obtained as output by the sliding mode control algorithm with reaching law.The models of compressor motor, compressor and vehicle compartment are simplified respectively. Model of equivalent object in temperature controller is series of these three equivalent object modes.Simulation research is under conditions with simplified control object model.The results show that the sliding mode controller based on reaching law is not sensitive to the change of thermal load;rise time is shorter and overshoot is smaller in this control system compared with which in the conventional PID control system.The electromagnetic noise of compressor in temperature control system mainly comes from the motor torque ripple.Study on the control strategy of the torque loop in temperature control system is of significance in reducing the torque ripple so as to reduce electromagnetic noise.Direct torque control has good restriction for torque ripple of brushless dc motor. Modified control mode of direct torque control without flux linage is adopted in this thesis.Under this condition, new modified voltage vector are selected and the classical PI closed-loop control speed controller is replaced with sliding-mode controller of reaching law. This control system can not only effectively simplify the traditional method of direct torque control but also has better inhibition for the current and torque ripple.