High Power Factor Control Of Pmsm Drive System Without Electrolytic Capacitor For Air-conditioner

Nowadays, permanent magnet synchronous motor(PMSM) drive systems are more and more widely applied in the field of home appliances to meet requirements of energy-saving and environmental protection. In the conventional motor drive system, the electrolytic capacitor has many shortcomings, such as short lifetime and poor reliability. Besides, the switching element and inductance of power factor correction(PFC) circuit in the drive system not only increase the cost of the volume, but also bring additional losses. The drive system called electrolytic capacitor-less drive system has many advantages such as high reliability, low cost and small size, which using film capacitor instead of electrolytic capacitor. However, this kind of electrolytic capacitor-less drive system would bring out low power factor, large amount of harmonics of input current and instability of the DC-link voltage. In order to solve the problems, the control strategies of electrolytic capacitor-less drive system for air-conditioner are investigated in this thesis.Since high power factor control of PMSM drive system without electrolytic capacitor is based on sensor-less control, a position observer for the air-conditioner PMSM drive is studied firstly. The stator voltage equation model in synchronous reference frame of the PMSM is established based on its structural characteristics. Then, the position observer of PMSM for air-conditioner compressor can be designed. The back electromotive force can be extracted effectively via the observer. By using phase lock loop(PLL), the position and velocity information can be obtained in order to achieve sensor-less control of the electrolytic capacitor-less drive system.The inverter output power adjustment strategy of the electrolytic capacitor-less drive system is studied, which focuses on controlling the output power of the inverter to achieve high power factor. The proposed strategy regards d-q axis current as a whole to generate the current reference to meet the average load torque requirement while minimizing the power error between the actual and the reference values. By using the output power compensator to compensate the power error, the inverter output power can track power reference effectively to meet high power factor requirements of PMSM drive system without electrolytic capacitor for air-conditioner.In order to enhance stable operation of the electrolytic capacitor-less drive system, the strategy to maintain DC-link voltage stable is proposed. Considering the phenomenon that the DC bus voltage is not stable, the inverter system is modeled and the DC-link voltage stability condition is derived. Then the DC-link voltage stabilization control strategy is studied, which aims to avoid occurrence of the DC-link voltage resonance phenomenon.On the basis of theoretical analysis and simulation verification, the proposed control strategies are validated on the electrolytic capacitor-less drive system of a 1.5P commercial air-conditioner based on TMS320F28034 DSP. The feasibility and effectiveness of the proposed control strategies are verified by the experimental results.