| Magnetic levitation bearing is a kind of bearing which makes no mechanical contact between rotor and stator by electromagnetic suction.Compared with traditional bearing,it has advantages of small mechanical wear,long life and low working environment requirements.It is widely used in high speed rotating machinery,oil free working environment,rotor active control and other fields.The power amplifier,as an important component of electromagnetic suspension bearing,changes the magnetic field formed by the coil by controlling the current flowing through the coil,and then controls the electromagnetic suction to the rotor part.Traditional magnetic bearing power amplifier is a kind of half-bridge switching power amplifier whose switching tube works in hard switching state,it requires a large enough radiator to conduct heat.High voltage change rate and current change rate will bring electromagnetic noise and interference.Aiming at the defect of power amplifier in hard switching operation,a new type of soft switching power amplifier is proposed in this paper.The topology inherits the working characteristic of traditional power amplifier to track and output given current,and realizes zero-voltage conduction of half-bridge structure switch tube by controlling dc bus voltage.In this paper,the main research content of power amplifier includes the following aspects:(1)According to the working principle of electromagnetic suspension bearing and the demand for power amplifier,the relationship between electromagnetic suction and coil current,the relationship between duty cycle and stable current,and the influencing factors of current ripple are deduced.(2)A new soft switching power amplifier for electromagnetic suspension bearing is proposed.Its working mode is divided by current flow direction,and the variation process of main electrical parameters such as bus voltage,voltage at both ends of each capacitor,current flowing through the inductor and the realization form of soft switching of each switch tube are analyzed under each working mode.(3)Considering the limitation of the number of coils and the difficulty of control,the simplified study of the new soft switching power amplifier is carried out.The precircuit and the back-end half-bridge switching device are simplified respectively,and then the current control ability of the simplified two power amplifiers is analyzed.(4)The PSIM software is used to simulate the new soft switching power amplifier,and the simulation waveform is used to verify the soft switching characteristics of each switching tube.By comparing with the hard switching power amplifier,the control ability of the new soft switching power amplifier on the coil current is studied.(5)Design the related hardware circuit of the magnetic bearing control system and assemble the magnetic bearing control platform,then analyze the operation principle and related performance of each component module.Based on DSP28377 D controller,the control program is designed according to the sampling circuit,the control requirements of displacement loop and current loop,and the control strategy of magnetic bearing power amplifier.(6)The soft switching characteristics of the new soft switching power amplifier are verified experimentally.The performance of the new soft switching power amplifier and the traditional power amplifier is studied by comparing the current output characteristic experiment and efficiency experiment. |
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