Modularized Modeling And Integrated Simulation Of Thermal Management Systems Of Electric Vehicles Based On Dymola

As an energy-saving and environmental-friendly way of transportation,electric vehicles(EVs)have gained tremendous attention and development in the past few years.At the present stage,vehicle-mounted power batteries are still dominated by Li-ion chemical batteries,whose performances are pretty susceptible to the temperature.Li-ion batteries will face with low energy efficiency when at low temperatures,thus from the perspective of saving energy,some heating measures should be taken.One the other hand,Li-ion batteries will also suffer from severe capacity loss when at both high and low temperatures,so from the perspective of lowering battery replacement cost,some temperature control measures are also required.To solve above problems,this paper,based on an electric coach project,designs a hydronic heating system to preheat batteries in winter and a double-evaporator air-conditioning system to cool the cabin as well as batteries in summer.With the help of Dymola that is suitable for modularized modeling and integrated simulation,the aforementioned thermal management systems(TMSs)are divided into sub-modules and corresponding sub-models are built.These sub-models are then integrated into TMS models in Dymola.TMSs' behavior and batteries' performances under different driving conditions and thermal management schemes are analyzed by simulation.According to the simulation results of the preheating system,the relationship between ambient temperatures,driving ranges and batteries' preheating demands is concluded qualitatively.As for the cooling system,the effect of different cooling methods upon batteries is validated.Eventually based on the actual project demand that batteries need to be preheated at subzero temperatures,the preheating system is optimized by determining its operating objective.Under the goal of minimizing vehicle operation cost,batteries' optimal preheating target temperatures under different ambient temperatures and driving ranges are determined quantitatively.Vehicle tests are also conducted in this paper.The detailed contents of this paper are as follows:(1)Domestic and oversea literatures related to relevant research areas are referred to.The research status of batteries' electro-thermal and degradation characteristics,EV TMSs' development and Dymola/Modelica's applications is particularly investigated.Consequently the research contents and focuses are confirmed.(2)Based on previous studies,the advantages and disadvantages of different thermal management methods are analyzed,as a consequence,liquid is chosen as the thermal management media.A hydronic preheating system which aims at low-temperature batteries is schemed;while a cooling system which aims at high-temperature cabin and batteries is schemed.The topology and working principles of the two systems are then analyzed.Parameter matching is also conducted towards the key parts of the two systems,so as to provide data for modeling.(3)After exploring the modeling mechanism of Dymola,the EV TMSs are divided into five sub-modules: power battery,charging pile,liquid heating,air-conditioner and cabin.Each module is studied in terms of working principals and built according to the characteristics of Dymola.Specifically the battery module is built based on the semi-empirical electro-thermal-degradation dynamic coupling model.(4)The modules of power battery,charging pile and liquid heating are integrated into preheating system,and then it is comparatively simulated under given driving cycles and environmental conditions.From the perspective of promoting battery energy efficiency and lowering capacity loss,the preheating demands of batteries under different conditions are qualitatively analyzed.It is concluded that the preheating demand is supposed to grow as ambient temperature falls;however it doesn't necessarily grow as the driving range increases.The modules of power battery,air-conditioner and cabin are integrated into cooling system,and then the influences of cooling system's interference upon battery performances are studied by simulation.The cooling effects with battery cooling methods being forced air,AC air and AC liquid are compared,and consequently the AC liquid method proves to be the best battery cooling method.(5)Vehicle operation cost is quantized into two parts: vehicle electricity consumption cost and battery fade cost.According to project demand,under the goal of minimizing quantized vehicle operation cost,the optimal preheating target temperatures are solved in Dymola with different ambient temperatures and driving ranges.Namely,it is clearly pointed out which temperature the battery should be preheated to by the preheating system under different conditions.The simulation results indicate that batteries' optimal preheating target temperatures are supposed to grow with decreasing ambient temperatures or decreasing driving ranges.Besides,according to analysis on simulation results,it is found that preheating process could add vehicle electricity consumption cost,but could noticeably lower battery fade cost.Under the comprehensive effects of the two factors,the preheating process could still significantly reduce vehicle operation cost.Finally the preheating system is implemented on a real vehicle,and corresponding vehicle tests are conducted to validate the accuracy of proposed battery model and the necessity of preheating at low temperatures.