The Research On Control Technology Of Air-condition Compressor Driven By Permanent Magnet Synchronous Motor

Permanent Magnet Synchronous Motor(PMSM)has been widely used in motor drive occasions because of its simple structure,easy maintenance, high efficiency, excellent performance. With the air-condition system performance and energy efficiency is becoming increasingly demanding in recent years, the traditional induction motor used in compressor has gradually been replaced by permanent magnet synchronous motor. This paper focuses and elaborates on permanent magnet synchronous motor-driven compressor, and explores new control strategies for the compressor load characteristics and energy-saving purposes.This paper first describes permanent magnet synchronous motor mathematical model in the static three-phase, two-phase stationary phase and two-phase rotating coordinate system. The vector control theory of PMSM and SVPWM modulation method are analyzed and discussed in detail. The principle of direct torque control is then introdued in brief. The rotor flux orientation method of id = 0 is selected to achieve the speed and current dual closed-loop program for permanent magnet synchronous motor-driven compressor system.As the air-conditioning compressor within the operating environment is very poor, the traditional mechanical position sensors can no longer be used, so sliding mode observer is used in this paper to estimate the rotor position and speed of PMSM real-time online. The principle of sliding mode observer and its model of PMSM in theα-βcoordinate system are also analyzed in detail. For chattering phenomenon and the speed of calculation accuracy is not high, approximate saturation function and differential phase-locked loop are used to replace the switching function and directly differential calculation method respectively.In order to reduce energy consumption of PMSM-driven compressor in air-conditioning system, a new strategy namely direct power control is proposed to achieve energy-saving purpose in this paper. Based on the analysis of relationship of the active power,reactive power,torque and stator flux-linkage, the direct power control (DPC) control method for PMSM is studied in detail. It selects optimum space voltage vector to control the instantaneous power through optimum switching table which based on the sector of flux linkage and the output of the active and reactive power hysteresis. The goal of the method is to control reactive power as zero and improve power factor at the same output of active power. Both the results of simulation and experiment show the good performance and accuracy of the proposed method. For a common permanent magnetic synchronous motor (PMSM) single rotor compressor system, cyclical fluctuation of the load torque causes the ripples of speed at the same cycle. The vibration of the air-conditioning system framework, high noise et al. phenomenon caused by the ripple speed is particularly evident when compressor running at low speed. And the efficiency of the system comes down at the same time. After analysis the impact on the system stability of such periodic speed disturbances in detail, a new method aiming to suppress the pulsation of the speed caused by periodic torque disturbance is proposed in this paper. A composite controller consisting of PI controller and repetitive controller which are paralleled together is placed in the speed loop. The PI controller and repetitive controller are used together in the steady-state for better performance of the steady-state, and PI controller is mainly to obtain good dynamic response when non-periodic disturbance appears. Simulation and experimental results show the feasibility and validity of the control program.The sampling of phase current is a core part in motor control. In this paper three-phase current measurement using only a single current sensor in the inverter dc link is proposed based on the relationships among the phase current, DC bus current and inverter switch states, it can minimize the number of current sensors, reduce sensor cost, weight, and volume. The new single current sensor algorithm can solve the difficulty in three-phase current reconstruction by space voltage vector phase-shifting. Simulation and experimental results show that the method is effective and correct.By means of Matlab software and digital control hardware platform, the above-mentioned theories and strategies are verified through simulations and experiments.