Research On Energy Management Strategy Of The Electromechanical Flywheel Electric Vehicle Based On Driving Condition Prediction

For the sustainable development of society,the development of efficient electric vehicles is imperative.At present,lithium battery has become the primary choice of energy source with the advantage of high energy density.However,under the condition of mutational load,the lithium battery will charge or discharge rapidly with high power current,which has the negative impact on the efficiency and life.Maenwhile,the lithium battery is affected by the chemical reaction speed of the "active substance",and the capacity for energy recovery is limited under the condition of high-intensity braking.Due to high power density and high efficiency for energy conversion,flywheel is suitable as an auxiliary energy source for electric vehicles,which can effectively reduce the negative impact of high power current on lithium batteries.The electromechanical flywheel electric vehicle adopts the electromechanical flywheel system,which forms a set of dual energy source and dual motor electromechanical flywheel composite energy storage system with lithium battery and main drive motor.First of all,according to the driving requirements of MPV,two system schemes are designed,which are electromechanical flywheel hybrid scheme(EFHS)and single motor direct drive scheme(SMDDS).The structure and working mode of electromechanical flywheel system are determined,and the working principle of each mode and the working state of each component are analyzed in detail.On this basis,the parameter optimization design of the two schemes is completed,then the efficiency of the electromechanical flywheel system in different modes is analyzed,and the operation range of the flywheel energy state SOE is determined.Secondly,the forward simulation models of electromechanical flywheel electric vehicle and electric vehicle are established by using Matlab/Simulink software,mainly including driver model,powertrain model,communication system model,control system model,etc.Among them,the driver model uses the speed following coefficient based on PID algorithm to calculate and output the driving and braking torque required by the vehicle;the powertrain model generates and transmits power,and completes the state update and control of the vehicle and its components according to the control signal from the control system.Thirdly,based on Markov chain,the conditions of J1015,NEDC and HWFET are predicted accurately.On this basis,the significance of condition prediction for adjusting flywheel energy state and recovering flywheel energy in parking recovery mode are studied.According to the complex modes of electromechanical flywheel electric vehicle,a logic threshold strategy based on condition prediction is proposed,which is divided into driving torque control strategy and braking torque control strategy.Among them,the driving torque control strategy introduces the intervention torque of electromechanical flywheel system to realize the effective intervention of electromechanical flywheel system;when studying the braking torque control strategy,the braking torque strategy based on I curve and ECE braking regulations is used,which can not only ensure the vehicle braking efficiency,but also increase the vehicle energy for recovery.Finally,through the analysis of the simulation results of electromechanical flywheel electric vehicle in the conditions of J1015,NEDC and HWFET,it is found that the energy management strategy can reasonably distribute the torque,ensure the normal operation of the motor and flywheel,and fully and quickly recover the braking energy.In addition,the condition prediction can increase the participation time of flywheel,transfer part of the low efficiency points of main drive motor to the high efficiency area of speed motor.Compared with the SMDDS,the EFHS has better acceleration and climbing performance In terms of economy,compared with the SMDDS,the EFHS can significantly improve the matching degree between the cycle condition and high efficiency area of the motor.Under the conditions of J1015,NEDC and HWFET,compared with the SMDDS,the average efficiency of the EFHS is increased by 8.2%,5.6% and 4.3% respectively,and the average power consumption per kilometer is reduced by 0.02 k W·h,0.03 k W·h and 0.048 k W·h respectively.In the EFHS,the flywheel plays the role of "peak shaving and valley compensation",absorbing or supplementing the residual power beyond the power of lithium battery,reducing the impact of instantaneous peak power on lithium battery,making the input and output of lithium battery stable,efficiency higher and life longer.