| In the electromagnetic bearing control system,the output characteristics of the switching amplifier play a key role in the design and stability of the entire system.Current ripple characteristics and different levels of PWM technology are the core technologies studied in recent years.For electromagnetic bearing systems,current-mode switching power amplifiers have higher system stability than voltage-based switching power amplifiers.Therefore,this paper focuses on current-mode switching power amplifiers.The main Innovation includes the following:First,under the premise of not involving the specific pulse width modulation strategy,a unified current ripple model based on the state function of the main circuit switch is established,and the basic principle of using the current ripple characteristics to realize the rotor displacement estimation is analyzed;The second is to combine the current ripple-rotor displacement model and the specific pulse width modulation strategy to analyze the characteristics of the output current ripple of the switch power amplifier from both time and frequency domains.The third is a new type of hybrid pulse width under the condition of the modulation failure of the traditional triangular wave comparison method three-level switching power amplifier.The modulation scheme was verified through simulation and experiment.Fourth,through the above theoretical research,the various hardware modules of the current-mode switching power amplifier of the electromagnetic bearing were designed.Taking the above innovations as context,the main research contents of this paper are as follows:First of all,this article summarizes the current research status of electromagnetic bearings and power amplifiers,and proposes the purpose,methods and other contents of this paper.Analyze the inductance characteristic of the electromagnetic bearing,establish the linearization model of the single degree of freedom electromagnetic bearing system under the differential control strategy,and then combine the characteristics of the current type power amplifier,voltage type power amplifier and magnetic flux power amplifier,analyze the main control scheme of the electromagnetic bearing.Secondly,the category of the electromagnetic bearing switch power amplifier and the main circuit topology are introduced,and the switch state equation is established.Then,the current ripple characteristics(coil current,current change rate,harmonic amplitude,etc.)are analyzed according to different levels.Then based on the characteristics of current ripple,the transfer relationship between the rotor ripple and its displacement is analyzed,and a unified transfer model is deduced.At the same time,a comparison of three current pulse width modulation techniques is used to compare the current ripple pattern with Matlab/Simulink simulation software.Then,the modulation failure mechanism of the three-level PWM switching power amplifier based on triangular wave comparison method is analyzed.Based on the three-level PWM switching power amplifier,a hybrid modulation method combining the triangular wave comparison method and the sample-and-hold method is proposed.The new power amplifier modulates the common bridge arm and the load bridge arm,and the common bridge arm adopts triangular wave comparison.In the method,the load bridge arm adopts an improved sample-and-hold method,and the bias voltage is set by the mean value of carrier amplitude and the quiescent current error,and the correctness of the design is verified through simulation and experiments.Finally,the design instructions of the designed hardware modules of the switching power amplifier are completed,and the hardware of the switching amplifier is made based on the Cadence design software.The linearity,harmonic distortion(THD),tracking characteristics,and current ripple are analyzed.Current response speed and other performance.At the same time,a step-down DC-DC switching power supply is designed based on the MP8675 chip to provide the power supply voltage of the position sensor.Then,a digital PID controller was used to complete the levitation experiment on the single-degree-of-freedom and single-side flywheel rotor electromagnetic bearing experimental platform,and the levitation quality was analyzed by detecting the rotor levitation position and the power spectral density curve. |
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