Research On Low-speed Bldc Performance For A Satellite Air Conditioning System

The air conditioning compressor, as the core of the refrigerating system, is a kind of driven fluid machinery which can boost low-pressure gas to high-pressure gas using piston driven by brushless DC motors(BLDC). BLDC is widely used in serve control, electric vehicles, robotics, and household appliances due to its simple mechanism, convenient maintenance, good speed regulation performance and high operation reliability. Efficient and precise starting and stable operating the BLDC is a prerequisite for the compressor to work normally. In the issue, we research on low-speed performance of BLDC in compressor based on the control of compressor in a satellite air conditioning system.On one hand, when the air conditioning system works, refrigerating fluid in the compressor has an effect on the position sensor. On the other, the engine oil in the compressor corrodes the position sensor. In addition, the compressor is designed to be sealed so that the position sensor can not be installed in the compressor. To sum up,we utilize BLDC without position sensor to drive the compressor which can cover the shortages, decrease the system failure rate, reduce the system mass, and lower the consumption of the compressor control system.In the control of the BLDC, measuring the rotor’s position precisely is a prerequisite for BLDC to commutate accurately. We get the rotor’s position of BLDC without position sensor indirectly by detecting the signals of back electromotive force(BEMF). To ensure the power supply of the other parts in the satellite, the air conditioning system should try to lower its consumption. So the BLDC is required to have a good low speed capability. However, it is impossible to exactly detect the rotor’s position because the BEMF signals are weak when the BLDC is at a low speed. By using the state-space equation, the Luenberger observer,with directly detected input signals, is able to estimate the current BEMF signals. We analyze and improve the observation capability of traditional sliding mode observer(SMO) and Luenberger observer. In addition, we simulate to prove the effectiveness of the designed observer. Finally, we do experiment on the hardware system, and estimate the BEMF signals of low-speed BLDC.The research originates from the design of micro refrigeration system controller project. Based on the sliding mode observer, we would design a compressor used in the satellite air conditioning system. The research is helpful to promote the sliding mode observer used in the satellite air conditioning system.