Research On The Control Strategy Of The Beam Power Supply Based On Fractional-order Control

With the development of deep space exploration globally,exploration tasks have become more and more frequent.As an advanced technology in space exploration propulsion technology,electric propulsion technology has been widely concerned.The beam power supply is the core component of the power processing unit of space electric propulsion system.By establishing an electric field between the two grids of the thruster,the beam power supply provides power for the aggregation,acceleration,and extraction of ionized xenon ions in the discharge chamber,thus generating thrust to realize the operation of spacecraft position keeping.Due to the influence of the distance between the spacecraft and the sun,the power processing unit of the electric propulsion system has very high requirements on the output voltage and power of the beam power supply to ensure the safe and reliable operation of the electric propulsion system in a wide range of working points.In the beam power supply’s past design,the circuit design was updated and reformed based on the application of the existing analog control chip and DC/DC module.In the face of the beam power supply’s performance requirements,such as wide range regulated output and smooth switching operation of multi-task mode,the use of analog control technology limit the performance improvement space of the beam power supply to a certain extent.Therefore,digital power supply technology can be applied to the design of beam power supply.Combined with its programmable,intelligent mode switching,timing management,online parameter adjustment,and other advantages,the fractional-order control strategy of beam power supply is studied.The main research work is as follows.(1)This thesis analyzes the topology selection and structure design of beam power supply at home and abroad based on combining the structure and working characteristics of the ion thruster electric propulsion system’s power processing unit.Combined with the development trend of digital power supply,this thesis expounds on the development demand of beam power supply digital control and summarizes the development status of fractional order control technology.(2)According to the design requirements of beam power supply,such as fast response,anti-interference,stable and adjustable output voltage in a wide range,the input parallel output series-parallel double full-bridge topology is selected to sort out the working modes of beam power supply dual full-bridge DC/DC converter in one control cycle.The switching principle of input parallel output parallel mode and input parallel output series mode is analyzed.According to the requirements of spacecraft thrust control,the switch timing,duty cycle,and phase-shifting angle are adjusted to realize the dual-mode switching of beam power supply.By analyzing the topology of beam power dual full-bridge converter,the small-signal model of full dual bridge DC/DC converter is established,which provides a theoretical basis for the research of beam power supply fractional order control strategy.(3)Considering a complete dual bridge DC/DC converter’s structural characteristics,a voltage-current dual closed-loop fractional-order PI~λcontrol strategy is proposed.In this method,by analyzing the topology of beam power supply dual full-bridge converter,based on the small-signal model of full dual bridge DC/DC converter,the voltage,and current double closed-loop control structure in the average current mode is adopted,and the fractional-order operator is approximated by the improved Oustaloup digital implementation algorithm,and the fractional-order PI~λcontroller is established.In order to optimize the parameters of the fractional-order PI~λcontroller to meet the control performance requirements of the beam power supply,an improved genetic algorithm is used to optimize the parameters of the fractional-order PI~λcontroller.The double closed-loop fractional-order PI~λcontroller is applied to control the beam power supply’s output voltage and current.Based on Matlab/Simulink simulation platform,the dual loop fractional-order PI~λcontrol is compared with the traditional dual loop PI~λcontrol under the conditions of load mutation,input disturbance,mode switching,and so on.The simulation results show that the fractional-order PI~λcontrol has better performance.(4)In order to solve the problem of the time-varying model in harsh external conditions during spacecraft mission,and because the fractional-order PI~λcontroller and the conventional PI controller do not have the function of online parameter tuning,it is challenging to realize the parameter self-tuning requirements of fractional order PI~λcontroller under different working conditions.Therefore,in order to ensure the stable and reliable operation of the beam power supply,the fractional-order PI~λcontroller should be used in the beam power supply.Based on the double closed-loop fractional-order PI~λcontrol and fuzzy control,the parameters of voltage and current loop fractional-order PI~λcontroller are adjusted.The optimal parameters of the controller are satisfied by fuzzy reasoning,and the design of the double closed-loop fuzzy fractional-order PI~λcontroller for beam power supply is realized.Based on Matlab/Simulink simulation platform,the fuzzy fractional-order PI~λcontrol,fractional-order PI~λcontrol,and traditional PI control are simulated and compared under different working conditions.It can be concluded that the fuzzy fractional-order PI~λcontrol has a minor overshoot and faster response speed under startup and mode switching and has better dynamic performance and robustness under input disturbance and variable load conditions.(5)The experimental results of fuzzy fractional-order PI~λcontrol are consistent with the simulation analysis,which shows the superiority of the proposed fuzzy fractional-order control strategy.Compared with fractional-order PI~λcontrol and PI control,the beam power supply based on fuzzy fractional-order control has excellent steady-state and dynamic performance and can achieve comprehensive range voltage stabilization.The output and working mode switch smoothly.