Research On Micro-arc Oxidation Load Equivalent Model And Current Type Pulse Converter

Micro-arc oxidation(MAO)technology is a treatment technology that uses pulsed power in the electrolyte to modify the surface of light metals.Since the pulse electrical parameters are very important to the processing effect of the micro-arc oxidation load,in-depth study of the demand of the micro-arc oxidation power supply and optimizing the power control have become the main research direction to further improve the technology.This paper focuses on the research of load equivalent model of MAO,parameter identification,the generation of special pulse waveform and pulse control strategy.Firstly,in order to explore the growth process of the oxide film under the conditions of the micro-arc oxidation process from the perspective of electrical load,In this paper,the equivalent load model of micro-arc oxidation is established,and the experimental data of micro-arc oxidation in different reaction stages are selected,the Forgetting Factor Recursive Least Squares(FFRLS)algorithm is used to identify the model parameters,and the load terminal voltage obtained by the identification parameter fitting is consistent with the actual measured load terminal voltage.The correctness of the load equivalent model and the accuracy of the parameter identification method are verified.Furthermore,according to the change rule of the load waveform after adding the negative pulse,the equivalent model of the first-order pure resistance load is analyzed and the relevant parameters are solved.Based on the results of model parameter identification,the parameter change rule is summarized,and the internal relationship between the growth process of oxidation film and model parameters is discussed,which provides theoretical guidance for power supply design.Secondly,according to the load equivalent model,the relationship between the micro-arc oxidation reaction and the pulse form is analyzed,and the pulse demand of current-type asymmetric multi-level is obtained.In order to realize this kind of pulse,a kind of pulse converter which with Buck+Full bridge is deeply studied,the working process of the converter periodically realizing pulse output is described.In order to meet the requirements of fast response of pulse current and low ripple current,an interleaved parallel Buck circuit is used,and the ripple expression of output current is analyzed and deduced.Aiming at the problems of large-range frequent fluctuations in load and sudden changes in output current during micro-arc oxidation reaction,a predictive current control method applied to the converter is studied.And aiming at the one-beat delay problem of the digital controller,a two-step prediction is introduced to compensate the predictive current control.Meanwhile the robustness of the predictive current control strategy under the condition of inductance parameter mismatch is analyzed.Finally,in order to verify the analysis of the pulse converter topology and control strategy,a pulse converter simulation model was built,and the system hardware circuit and software program were designed,and an experiment platform was built.The result of Simulation and experimental show that the pulse output converter can achieve asymmetric multi-level pulse output with independent adjustments of pulse amplitude,duty cycle and polarity,and can meet the needs of different micro-arc oxidation load pulses.The designed two-step predictive current control can make the output current pulse reach the expected value quickly under various abrupt conditions,and improve the dynamic performance and anti-interference of the pulse output converter.