Electrolytic Capacitor-less Control Strategy For Air-conditioner Pmsm Drives

Variable frequency controlled permanent magnet synchronous motor(PMSM) drive systems are widely used in household appliances, especially in air-conditioners. PMSM drive compressor can improve the performance of system as well as reduce the consumption of the energy by a large margin. In recent years, the short lifespan of the electrolytic capacitor has become a key factor making the fault of drives, and traditional PFC circuits in air-conditioner PMSM drives need using inductances and power switching devices, which increase the cost of the systems. By replacing electrolytic capacitors with film capacitors, the reliability of the drive systems can be improved. Meanwhile the cost and the volume can be reduced. However, it would bring about the vibration of DC-link voltage and large amount of harmonic current on the line side at the meantime, making it difficult to control the motors. To improve the performance of PMSM drive of the air-conditioner, the control strategy of air-conditioner PMSM drive with electrolytic capacitor-less is investigated in this thesis.As electrolytic capacitor-less control is based on sensorless drive system, a position observer for the air-conditioner PMSM drive is studied firstly. According to the mathematical model and the transformation of coordinates, an extended electromotive force(EMF) model is built and then the position observer of air-conditioner PMSM can be designed. Then the rotor position information is effectively extracted by using phase lock loop(PLL), which is critical for the research of electrolytic capacitor-less and position sensorless drives.To solve the problem of the current reconstruction in the region where the current fails to be sampled at high speed, a reconstruction method of phase current using the three-shunt sampling based on pulse width modulation(PWM) phase shift is proposed. On the basis of analyzing the principle of phase current reconstruction, the immeasurable region can be gained. According to the four different regions where the phase current cannot be sampled, the voltage vector is injected to compensate for reference voltage. Due to the adjustment of the phase shift of PWM, the sampling time of the current is greater than the minimum sampling time, and then the valid reconstructed current is obtained which provides the feedback signal for the current closed loop control of the electrolytic capacitor-less drive.The control strategy for the electrolytic capacitor-less drive based on output power control of the inverter and DC-link voltage feedback is studied. Mechanisms of d-q axis current reference distribution and d-q axis voltage compensation which can realize high power factor are established. After analyzing the relationship between the input current and the load power, the implement approach to improve power factor is clarified. The current control strategy for q axis is based on the adjustment of inverter output power and employing a proportional resonant(PR) controller. Meanwhile, the d-axis current adopts field-weakening control to improve the power factor of the system further. After that, the stability of DC-link voltage is analyzed. Then the DC-link voltage control strategy is adopted by injecting the compensation voltage on the output voltage of current controller. Therefore, the stability of the DC-link voltage is realized.On the basis of theoretical and simulation analysis, the proposed electrolytic capacitor-less control strategy is realized by using a TMS320F28034 DSP, and the feasibility and effectiveness of the proposed control strategies is validated on a 1.5P media air-conditioner PMSM drive.