The Research On Variable Frequency Control System Of Movable Air Conditioner

Variable frequency air conditioner becomes widely used because of its advantage of comfortability, low power consumption, high temperature control accuracy and so on. Therefore, the study of its controller is vitally important. The application of movable variable frequency air conditioner aims at some specific places such as communication center ,oil rig electrical control center and military command center powered by movable power station. So it is important to study the variable frequency air conditioner control system in order to improve working environment and enhance working efficiency.As the core partial of variable frequency air conditioner, the compressor's control performance is vital to the whole system. Main circuit and corresponding control strategies of movable air conditioner compressor variable frequency control system are studied in this paper.Movable power station is low-capacity independent electric network. So it has severe demand of harmonic suppression. According to this characteristic of movable power station,PWM rectifier is introduced to air conditioner converter. Topology and current control strategy of three phase three-level PWM rectifier is studied in this paper. Harmonic analysis of input voltage and current have showen that harmonic distortion is reduced effectively,and power factor is improved.The main circuit of air conditioner converter is symmetric three-level structure, PWM control strategy both adopt Space Vector Pulse Width Modulation-SVPWM technique. Based on systematic analysis of principle and general modulation method of two level SVPWM,a low switching consumption SVPWM algorithm of three-level converter is studied in this paper.Speed ripple of compressor motor is serious in low speed range when constant voltage-frequency ratio control method is adopted. To solve this problem, speed sensorless vector control scheme is used in air conditioner variable frequency control system. Closed-loop control of the motor speed is implemented through speed estimation and rotor flux observation. Simulation results have proved that the control system has sound static and dynamic propertities at low speed.The control system is implemented using 16 bit digital signal controller dsPIC30F6010A. Both harware and software of the control circuit are designed.