Research On Magnetic Bearing Power Amplifier And Low Power Control

Magnetic bearing is a new type of bearing that keep rotor suspended stably by controllable electromagnetic force. It eliminates friction and wear which exists in traditional mechanical bearings and has many advantages, such as high speed, long life, no lubrication, and which conditions can be monitored. Since it appeared at the beginning, it attractes the industry and academia’s attention. This paper focuses on switching power amplifier and low power controller on magneitc bearing.First, in order to save axial space of long roter in magnetic bearing, a new method of axial displacement detection is described. The eddy current sensors are radial symmetrical installed and rotor axial displacement is measured by use of characteristic of eddy current sensor which sensitive to the stepped surface. According to mathematical arithmetic processing with two sensors output, it eliminates the influence on the detection result of the variation of the radial distance between the sensor coil and object. Gaussian noise which existes in the output voltage of sensors are analysed in time domain and frequency domain. The result shows that noise is main existed in low frequency domain. Kalman filter method is used to estimate the signal of rotor displacement, it reduces the influence of noise and improved the signal-to-noise ratio. This detection method used in maglev blower, the results show that it has a good linear relationship and sensitivity between the sum of two sensor output voltage and the rotor axial displacement, which realize accureate measurement and space-saving target.Three-level pulse width modulation switching power amplifier based on FPGA(Field Programmable Gate Array) is studied, Simulink-based mathematical model is established to simulate the FPGA in Embedded MATLAB Function module workflow. A method of construction disturbance observer is presented to compensate time delay in digital switching power amplifier, The time delay in the forward passage are equivalent to the input as a disturbance to compensate the time delay, and the disturbance is estimated by constructing a disturbance observer and switching power amplifier time delay compensation is realized and then the impact of the load parameter perturbation to the delay compensation effect is analysed. On the basis of the nonlinear phenomena analysis of two-level switching power amplifier, nonlinear phenomena in three-level switching power amplifier is studied. For the Full-bridge topology in the magnetic bearing three-level switching power amplifier, the existing chaotic behavior of full-bridge converter are studied. First, the a non-linear model of the full-bridge converter is established by using the stroboscopic map method, bifurcation stability and chaos characteristics are analyzed and the current control proportional coefficient, the carrier frequency and the stable region of the power supply voltage are calculated and determined by numerical computation, and Lyapunov exponent is calculated to verify the existence of chaos, which reveals the stable operating range of the parameter.In order to reduce the quiescent current loss of the magnetic levitation bearings, zero power control is studied. Displacement feedback method is used to improve the stiffness of control system to ovecome the characteristics of low stiffness in zero power control. In order to achieve compromise of stiffness and low power, switching function is designed. Zero power control based on variable stiffness is varified in maglev artificial heart pump, which reduces power consumption and has enough stiffness and damp.