Study On The New Low-Power Hybrid Magnetic Bearing With Bias Permanent Magnet

Magnetic bearing suspendes rotor with noncontact magnetic force, realizes the zerofriction running between rotor and stator. Magnetic bearing has the advantages of zerofriction, low noise, ultrahigh speed and long service life etc, can be applied to the domains of wind power generator, ultraclean vacuum environment, high speed machine, mechanical processing, rotating motors, transport and medicine etc.In order to solve the present problems of magnetic bearing structure, such as gravity disturbance, high power consumption, magnetic path coupling, complicated control, and high cost, etc., the paper puts forward a new structure of low-power hybride magnetic bearing with bias permanent magnet. It adopts the "up-suction and down-repulsion" permanent magnet force to counteract the gravity of rotor; it adopts the repulsion force between electromagnet and permanent magnet to adjust radial displacement of rotor, the coil current of±X and±Y directions can be changed by the method of simultaneous increase or decrease, or by the arithmetic of PID (Proportion Integration Differentiation); it also adopts the suction force among iron plate, electromagnet and permanent magnet to adjust axial displacement of rotor, the bias current is zero at axial direction, thus the current consumption can be lower. On the base of material research, the paper deduces the expression formula of gravity counteract force, radial adjusting force, axial adjusting force, which is consistent with the magnetic bearing structure, then gets the mathematical model, the displacement rigidity coefficient, the current rigidity coefficient, the transfer function of S domain under single degree-of-freedom (dof) and five dof, simulates the flow direction of magnetic force lines in magnetic bearing structure, and simulates the five dof movement of magnetic suspension rotor.The paper also researches the double closed-loop control system of hybrid magnetic bearing, which adopts the no sensor detecting method of "high frequency injection and parameters estimation" to measure the displacement of rotor at outer loop, also adopts the HALL current device ACS712 to measure the coil current at inner loop, thus abandons the displacement sensors of electricity eddy, cuts the cost lower, improves the response speed of coil current. Designes the control circuits of 10 current inputs,5 displacement inputs, as well as 10 PWM (Pulse Width Modulation) outputs, gets the circuit relationship between inputs and outputs, gets the transfer function of control circuit, gets the transfer function of double closed-loop control system, simulates the response curve of traditional PID control system. For the control demand of imprecise mathematical model, non-linear, uncertainty, unknown system, the paper studies on the neural network PID algorithm which is based on RBF (Radial Basis Function) prediction model, through off-line and on-line training of neural network, the weights values are revised continuously, so improves the robustness and adaptability of system, simulation shows that the response curve of neural network PID control system has less overshoot and shorter stable time.The paper builds a magnetic suspension experiment platform, draws the software flowchart, developes the procedure code of CCS and VC++, gets the experimental data and curves, the experiment shows that displacement fluctuations of magnetic suspension rotor is within±0.1 mm, coil current fluctuations is within±0.4A, the raotor has been suspended noncontactly, and the displacement fluctuations is smaller under the control method of simultaneous increase or decrease, the current consumption is higher. Optimizing the control strategy, reducing displacement fluctuation of rotor and current consumption of magnetic bearing, improving overall performance would be the next work.