Study On Self-sensing System Of No Displacement Sensor Magnetic Bearing

Magnetic Bearing is a electromechanical product, which involves mechanics, rotor dynamics, control theory and control engineering. It is a kind of bearing making use of magnetic force to suspend the rotor in the air without mechanical contact between rotor and stator. Compared with the conventional bearings, it has a series of merits such as no mechanical wear, low energy consumption, no lubrication, long life and so on, and has a broad application foreground in energy, transportation, machinery, aerospace and other fields.In order to accurately measure changes in air gap, magnetic bearing needs more displacement sensors, which makes the cost much high, the size larger and the dynamic performance and reliability of the whole system both decrease. Due to the limitation of the system structure, displacement sensor can not be installed in the middle of magnetic bearing making the system controller design become complicated. Therefore, It is necessary to apply self-sensing technology in magnetic bearing without displacement sensor into the bearing rotor suspension control system, which can overcome these deficiencies and reduce the cost of bearing.The paper introduces the basic theory of magnetic bearing without displacement sensor, sets up math model of rotor with single freedom and finds inductance of the bearing windings. There mostly are two methods in self-sensing of magnetic bearing without displacement sensor, differential transformer and small test-signal injection. Test-signal is rather hard to capture adopting the former one, but the later one is simple and the detecting-signal is accurate that when a small magnitude signal is injected into the input of the linear power amplifier, rotor displacement change information can be acquired by detecting inductance of electromagnatiam windings.The small-signal injection self-detecting system is studied thoroughly in the paper, and sets up software and hardware sructure of the system. Software design mainly aims at fuzzy adaptive PID controller applied in self-detecting system, and hardware design aims at detecting circuit and the continuous linear power amplifier. Finally simulation and debugging of the system are carried out.