Research On Measurement And Control System Of Active Magnetic Bearings

With the excellent features of non-contact,wear-free and lubrication-free,active magnetic bearings are widely used in vacuum systems,high-speed turbo machines,medical devices and so on.In a typical active magnetic bearing system,a controller collects position information of a rotor in real time through displacement sensors,calculates electromagnetic forces needed to control the rotor,and drives electromagnets through power amplifiers to achieve the rotor suspension.At present,the development trend of AMB systems is ultra-high speed,highreliability,low cost,miniaturization and so on.In order to meet the needs of measurement and control of high-speed AMB systems,this paper studied a new low-cost displacement sensor,a multi-core architecture control platform and a low noise switching power amplifier.The displacement sensor is one of the important components in a high-speed AMB system,which directly determines the control accuracy of the rotor.In this paper,a new radial displacement sensor called transverse flux sensor was discussed,which has obvious advantages in low-cost and miniaturized AMB system.The theoretical model of the sensor was established at first,and then with the help of FEM software in modeling and simulation,a PCB sensor probe was optimized and a set of design guidelines was summarized.Furthermore,the sensor test platform was designed and constructed accordingly.The static performance test results showed that the sensor had a sensitivity of 38.94 mV/μm,a linearity of 1.87%,a low X-Y coupling degree of 2.14% and a theoretical bandwidth of9.54 kHz,which could satisfy the displacement detection demands of an ultra-high speed AMB system.This sensor was applied to the displacement detection of the rotor of an air compressor and the compressor achieved stable suspension at the speed of 12,000 rpm.A control platform is the core of AMB systems,and complex high order control algorithm has put forward higher requirements for the controller’s operating performance.The paper designed and built an AMB control platform based on FPGA+DSP+ARM multi-core architecture.Compared with the previous generation of lab’s platform,its operational performance increased about 1.7 times.Compared with a traditional DSPbased platform,by introducing the FPGA in charge of signal I/O and preprocessing,the DSP can fully exert its computing performance.Besides,the introduction of the ARM makes up the insufficient expansion ability of the DSP and strengthens the DSP’s controllability and flexibility.A power amplifier plays an important role in the actuators of an AMB system.The paper introduced the working principle of a three-level switching power amplifier and built a current-mode three-level switching power amplifier with a gain of 2.04 A/V,a bandwidth not less than 1.35 kHz,and a current ripple not higher than 1.60% of its bias current.In addition,the modular design effectively reduces the interference between strong currents and weak signals,and channels of the power amplifier can be assembled on demand with more flexible.The multi-core architecture control platform and the power amplifier were applied to a magnetic helium cold compressor.The rotor of the compressor was levitated stably at a speed of 40,000 rpm and the rotation accuracy of the rotor is 10 μm,and the performance of the entire AMB measurement and control system was proved.