Research On Parameter Matching And Energy Management Strategy Of Pure Electric Vehicle Compound Power Supply

In the context of the current energy crisis and increasingly serious environmental pollution,it has gradually become an international consensus to vigorously develop energy-saving and new-energy vehicles to reduce dependence on fossil energy and reduce air pollution.It is also a key area of China’s strategic emerging industries and "Made in China2025".According to statistics from the China Association of Automobile Manufacturers,the annual production and sales of New energy vehicles in China reached 794,000 and 777,000 respectively in 2017,ranking first in the world for three consecutive years,and the total promotion volume has exceeded 2 million so far.Obviously,the new energy automobile industry has ushered in an unprecedented significant development opportunity,which at the same time drives the rapid development of the power battery system industry.However,the current power battery system technology is difficult to meet the multiple requirements of high specific power,high specific energy and low temperature and high start-up power at the same time,so the development of power battery and supercapacitor composite power system has become an effective solution.The key technology of designing composite power system is the parameter matching and energy management.At present,the energy management strategies of electric vehicle composite power supply mainly include logical threshold control,power distribution control based on speed and fuzzy logic control.Optimal capacity design,accurate energy state estimation and power demand prediction are the prerequisites for optimizing system performance and establishing efficient energy management strategy.In this paper,an optimized fuzzy control method for power distribution of power cells and supercapacitors is presented.The method based on genetic algorithm(ga)theory to the power battery energy loss in the circulation condition of minimum as cost function,according to each moment power battery and super capacitor charged state,by controlling the power output of the super capacitor in each moment to implement power battery and super capacitor between the optimal allocation of power.An effective energy management strategy was established to improve the efficiency of the composite power system.Finally,an experimental platform was set up to study the composite power system.Specific research work includes:First,the composite power supply parameter matching.The matching of composite power is divided into energy configuration and power configuration to determine the number of series and parallel of power battery and ultracapacitor.Together,they guarantee the energy and power requirements of the composite power supply.And the specific energy,specific power,specific price parameters of energy storage components and the design scheme of the whole vehicle constitute the constraints of system parameter matching.Three working conditions,UDDS,SC03 and NEDC,were selected for analysis in this paper.By combining the three working conditions,the capacity cost of capacitor and the life cost of battery were selected as the optimization goal,and finally a reasonable configuration scheme of the composite power system was obtained.Second,composite power modeling.As a component of composite power system,the accurate modeling of power battery and supercapacitor is one of the important contents in the research of composite power system,and the accurate modeling is the foundation of the control and energy management of composite power system.In this paper,the structure of the composite power supply is firstly determined.PNGV model is selected for the power battery model.The model is simple,the parameters are easy to identify and the accuracy is relatively high.In this paper,the classic RC model is selected to identify the parameters in the model in order to obtain accurate state values,that is,to obtain relatively accurate model parameter values,which can be used for subsequent state estimation and energy management strategy formulation.The sensitivity of DC/DC is relatively high.In this paper,the transient response is not taken into account.Instead of the simulation model,a two-dimensional efficiency model is established to complete the overall modeling of the composite power supply with the established model.Third,research on energy management strategy of composite power source.In order to decrease the power battery charging/discharging rate and surge current,improve the system of high power charge/discharge ability,the purpose of energy management strategy in the process of system working power battery is required to provide stability and the demand of low frequency power,ultracapacitors provide peak power,high frequency power for a short period of time,and most of the braking energy recycling.The biggest advantage of fuzzy logic control is that it can realize smooth transition between regions and states according to the set working area,and at the same time it can show some fuzzy concepts that cannot be determined by rules.In addition,the fuzzy control is optimized according to the genetic algorithm theory.The structure of fuzzy optimization controller based on genetic algorithm is determined.Fourth,the composite power system hardware in the loop experiment.According to the existing laboratory equipment,build a compound power bench experiment,compared with the result of optimization of before and after optimization analysis,get the optimized control strategies significantly reduces the output current of power battery,the power battery power output is more stable,improve the energy efficiency of the vehicle,extended the travel distance of,verify the effectiveness of the energy management strategy.