| The magnetic levitation drive platform has the advantages of no mechanical contact,easy to driver with multiple degree of freedom,fast response,etc.It is widely used in precision machining,dust-free transmission and other fields.Due to the characteristics of the inductive load of the magnetic suspension platform,there is a charge and discharge phenomenon when the power amplifier is driven,which will produce a large current ripple and current lag.It directly affects the control effect of the entire magnetic suspension system.The methods for reducing the current ripple in power amplifier all adopt three-level control.The existing methods for implementing three-level control make the structure of the power amplifier circuit complicated and difficult to debug.In addition,the current controller of the power amplifier mainly uses PI control,which has a long dynamic adjustment time and poor robustness.There are certain danger of setting PI parameters in high-power applications.In view of the above problems and deficiencies,this dissertation uses STM32 to design a new three-level PWM switching power amplifier.The specific work content is as follows:Firstly,the modulation strategy,working principle and current ripple of the two-level and three-level switching power amplifiers are analyzed and studied in detail.The mathematical analysis formulas for the current ripples of two PWM switching power amplifiers are derived.The simulation and experimental analysis verify that three-level switching power amplifier can reduce current ripple.Then the current response speed characteristics of switching power amplifier is analyzed,and the conditions for switching power amplifier to track the current given signal without distortion is given.Secondly,the control method of three-level switching power amplifier is studied.The three-level switching power amplifier simulation model is built in Simulink.The controller uses PI control.It is found that the switching power amplifier has a long dynamic adjustment time,poor parameter robustness,large steady-state error.A fixed-frequency current predictive control algorithm is proposed to improve the above problems.The algorithm is theoretically analyzed and compared with traditional PI control simulation experiments to verify the feasibility of fixed-frequency current predictive control.The results show that the dynamic adjustment time can be effectively reduced,the current response speed and steady-state accuracy can be improved.Then,the traditional three-level PWM modulation principle is studied and its shortcomings are analyzed.An improved three-level PWM modulation method is proposed and compared with the traditional three-level PWM modulation method.The results show that the improved three-level PWM modulation method can reduce the current ripple and the complexity of power amplifier circuit structure.Finally,according to the guidance of the above theoretical research,the development of the hardware circuit system and software system are completed.A physical prototype of the switching power amplifier is made.The validity and feasibility of the design are verified by the relevant output characteristic experiments,and the experimental results shows that the new three-level PWM switching power amplifier has small output current ripple and fast current response speed. |
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