| Magnetic bearings as a new type of controllable support device,with its non-contact and stiffness damping adjustable and other unique advantages are widely used in aerospace,transportation and energy and other fields.As one of the most important parts of the control system,the switching power amplifier has the biggest interference and the most serious lag.Therefore,it is necessary to improve the performance of the switching power amplifier in order to improve the bearing capacity of the whole magnetic bearing system.In this paper,the performance of the switching power amplifier is studied in all aspects from the theoretical analysis,the experimental verification and the simulation verification,and applied to the platform of magnetic bearing system with five degrees of freedom on the suspension experiment,the following is the main content of this article:Firstly,the advantages and disadvantages of different types of magnetic bearing switching power amplifier are compared and analyzed from the perspective of mathematical model.The coil current model of the magnetic bearing is established by single coil and double coil winding.The advantages and disadvantages of the half bridge and full bridge switching power amplifier are compared and analyzed.The mechanical model and the dynamic model of the magnetic bearing and the electrical model and transfer function model of the switching power amplifier are established.The current and voltage switching power amplifiers corresponding to the two control schemes are compared and analyzed.And the current ripple model of two level and three level switching power amplifier is established.The advantages and disadvantages of these two levels of switching power amplifier are compared and analyzed.Secondly,based on the mathematical model,the characteristics of the magnetic bearing switching power amplifier are analyzed theoretically and experimentally.In view of the half bridge,current type,three level PWM switching power amplifier used in our laboratory,the electrical parameters of the load coil inductance,switching frequency,frequency bandwidth,drive current,power supply voltage and power device are determined.The performance indexes such as efficiency,distortion,current ripple,current response speed and output characteristics are studied.The influence of the selection of the electrical parameters of the switch power amplifier on its performance index and the whole magnetic bearing system is also discussed.The reason and harm of the distortion of the switching power amplifier are revealed,and the relationship between the current ripple,the response speed of the current and the frequency and duty cycle is analyzed and experimentally verified.Moreover,the interference of the switch power amplifier is also introduced.Thirdly,based on the distortion analysis,the characteristics of the magnetic bearing switching power amplifier are improved and verified by simulation.A kind of digital switching power amplifier based on fuzzy control is proposed to improve its hysteresis distortion.The simple circuit design,program design and anti-jamming design of the digital switching power amplifier based on hardware and software are introduced.The hardware circuits such as current feedback circuit,signal sampling circuit,phase shift PWM circuit,isolation drive and protection circuit,and software program such as system main program,interrupt service routine are analyzed.The simulation results show that this digital switching power amplifier based on fuzzy control improves its tracking performance and restrains the magnetic interference very well.Finally,the switching power amplifier is applied to 10 kWh flywheel energy storage system magnetic bearing prototype for static and dynamic suspension experiments.In the static suspension experiment,the rotor displacement,coil current and sensor output voltage of axial and radial magnetic bearings are compared and analyzed.In the dynamic low speed suspension experiment,the rotor displacement and coil current of axial and radial magnetic bearings is compared and analyzed.In the dynamic high speed suspension experiment,the rotor displacement,amplitude spectrum,phase spectrum,power spectrum and axial trajectory of axial and radial magnetic bearings are compared and analyzed.The suspension results show that the rotor of the magnetic bearing can be suspended in the ideal position at the axial and radial degrees of freedom,that is to say,the switch power amplifier researched in this paper can basically meet the requirements of the magnetic bearing system. |
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