Beat-less Control Strategy Of Electrolytic Capacitor-less Air-conditioning Motor Drive System

The variable frequency air conditioning has many advantages,such as self-regulating room temperature,comfortable user experience and low energy consumption.The variable frequency air conditioning has a great significance for energy saving and emission reduction.The permanent magnet synchronous motor has the advantages of high power density,high dynamic performance and flexible control.It is widely used in the air-condition field.The using of electrolytic capacitor in the traditional air conditioning motor dri ve system reduces the stability of the system.For this purpose,the electrolytic capacitor is replaced by the film capacitor and the power factor correction link is taken out,which is the electrolytic capacitor-less drive system and it can effectively reduce cost and increase the system lifetime.The capacitance of the used film is small and the dc link voltage fluctuates at twice the grid frequency.In the end,there is beat phenomenon when the motor runs at specific running frequency.In addition,the decrease of the capacitor will influence the system stability.Therefore,this paper studies the beat phenomenon issue and the stable operation control in the electrolytic capacitor-less air condition motor system.Firstly analyzing the permanent magnet synchronous motor operating principle and the mathematical model of motor under different coordinates is obtained through the comprehensive vector.Based on the analysis above,the double closed-loop vector control strategy is analyzed.The permanent motor model in two-phase rotating coordinate obtained through coordinate transformation is linearly decoupled.Therefore,the vector control strategy is adopted in this coordinate to make the excitation component and torque component of stator current decoupled.To eliminate the beat phenomenon that exits at specific operating frequencies,a beat suppression strategy based on the current tracker is studied.Through the analysis of beat phenomenon when motor runs at specific frequencies,here comes the conclusion that the fluctuating dc link voltage is the root cause for beat phenomenon.The modulated wave movement is calculated by the current tracker and a voltage compensation will be obtained,which can compensate the motor stator voltage deviation caused by the fluctuating dc link voltage,then the beat phenomenon is suppressed.Then the beat phenomenon is eliminated.The effectiveness of the studied strategy is verified through the simulation.In order to improve the stability of the electrolytic capacitor-less air condition motor system,the active damping control strategy is studied.Based on the models of input and output impedance and the analysis of characteristic of models,the current and voltage two kinds of active damping control strategies are proposed and then the corresponded input impedance models after using the control method are derived.Through the analysis of the system characteristic equation and the total impedance frequency characteristic,the effectiveness to improve the system stability of the studied active damping control strategy is verified.The effectiveness of the active damping control strategy is verified through the simulation.Finally,based on the analysis of theory and simulation,the current tracking method to depress the beat phenomenon and the active damping control strategy to improve the system stability are realized by digital algorithms and verified in 1k W electrolytic capacitor-less air condition experiment platform.Experimental results demonstrate the effectiveness of the proposed methods.