Research On Linear Active Disturbance Rejection Load Control For Stable Operation Of Free Piston Electromechanical Hybrid System

Because of its unique composition and operation,Free piston electromechanical hybrid system（FPEHS）is regarded as a new power unit with great potential for development due to its simple structure,variable motion stroke and small friction loss.FPEHS can be used as a driving system for electric vehicles or as an auxiliary power for mobile delivery vehicles.However,the removal of crank connecting rod also makes it face some problems,such as unstable motion,difficult starting and misfire.Nowadays,one of the key technologies hindering the practical and industrial development of FPEHS is the lack of reliable motion control.In order to ensure the advantages of the unique structure of FPEHS and promote its industrialization,reliable motion control is indispensable.To solve the problem of FPEHS operation instability,a control strategy is designed to realize the operation stability of FPEHS by adjusting the load under the change of combustion,and theoretical analysis and simulation calculation verify the feasibility of the control strategy.Based on the power transmission path and system dynamics of FPEHS,the mathematical model of FPEHS is established with the help of thermal,electrical,magnetic and nonlinear dynamics theory.The FPEHS operation simulation model is constructed through the Matlab/SIMULINK simulation platform,and the validity of the model can be proofread by the test results and the mutual proofing of the simulation calculation results.In addition,the linear active disturbance load control（LADRC）model is coupled on the FPEHS mathematical model.The combustion variation is taken as the interference factor in the operation of FPEHS,and the specific form is the fluctuation of input energy.Given the expected trajectory of FPEHS,when the interference factor causes the error between the real time trajectory of FPEHS and the expected trajectory,the LADRC processes the error signal to adjust the electromagnetic force to control the trajectory of the piston assembly,so as to achieve the stable operation of FPEHS.This paper compares and analyzes the system performance of FPEHS under the action of LADRC and the classic PID controller when the interference factor appears in the start up stage and the operation stage.The results show that in the absence of controller,whether the interference factor appears in the FPEHS start up stage or the operation stage,it directly lead to changes in its operating frequency and operation stroke,When the input energy is reduced below380j,the FPEHS stops operation directly.When using the controller,either the LADRC controller or the PID controller can maintain the stable operation of FFEHS when the interference factor appears,but there are still some differences in the control performance between them.When the interference factor appears,the PID controller has a large overshoot phenomenon,and the system needs a long time to achieve stable operation;while the use of LADRC controller,FPEHS no obvious overshoot phenomenon,with good start up performance,and control accuracy is higher than PID controller more than one magnitude level.The different choices of observer bandwidth,controller bandwidth,and control gain（w₀,w_c,and b₀）have a significant effect on the operational performance of FPEHS.The increase of w₀ from 5 to 13 and w_c from 3 to 11 will increase the load coefficient,which causes LADRC to give off a stronger control effect.The electromagnetic force of the linear motor enhances,the thrust of the piston assembly weakens,and the running cycle of the piston assembly increases due to the decrease in velocity and acceleration.However,the continuous increase of w₀ and w_c abate the control accuracy of LADRC,and the compression ratio fluctuates.The effect of b0 on FEHS is the opposite of w₀and w_c.The increase in b₀ reduces the control effect,shortens the range of fluctuations in electromagnetic forces,accelerates the running cycle of piston assembly.When the b₀ value is small,the FPEHS compression ratio curve fluctuates significantly.With the increase of b₀,the compression ratio becomes stable.But,the excessive b₀ value weakens the control function of the LADRC controller,resulting in a gradual increase in the difference between the real time trajectory of the piston assembly and the desired trajectory.