Research And Control Analysis Of Electric Vehicle Refrigerant-based Thermal Management System

To cope with the thermal safety of high-energy power batteries and the thermal requirements of vehicles with complex and changeable working conditions,the thermal management system is gradually moving to a efficient and lightweight heat transfer structure,an integrated heat flow cycle,and an intelligent linkage control system.A functional thermal management system of the whole vehicle is formed to promote the development of electric vehicles with high safety,strong power,long life,low energy,and excellent comfort.Refrigerant-based thermal management system with high heat exchange capabilities has been concerned and pondered.Regards to the new heat transfer mode of refrigerant-based thermal management,relying on the means of experiment and simulation,this paper probes into the heat and flow characteristics,system structure layout,dynamic control strategies and cooperative optimization management of electric vehicle thermal management system.The experiment bench of integrated refrigerant-based thermal management of electric vehicles is built to meet the thermal needs of power battery pack and cabin.The heat and flow characteristics and regulation rules of the battery circuit is tested.The results show that the relationship between the refrigerant evaporation temperature and battery stabilization temperature,and there is a heat transfer saturation in refrigerant flow and heat exchange capability.Further,the cascade parameter control strategy of giving priority to battery temperature drop and then ensuring battery temperature difference is proposed.Specifically,the corresponding optimal refrigerant flow and target temperature limit values are preferred at different battery discharge rates,providing a new idea to control the battery thermal behavior.Based on the experimental platform in the above chapter,the battery thermal management system and air conditioning system are taken as the main research object.A three-dimensional battery heat transfer model and a one-dimensional integrated thermal management system model is built to further explore the heat transfer interaction and control mechanism of electric vehicle integrated refrigerant-based thermal management system.By identifing the performance parameters of the system and components and characterizing the thermodynamic state of working fluid,a theoretical basis for the establishment of an intergrated refrigerant-based thermal management system is provided.The results indicate that the simulation model has high accuracy and reliability,and can be used for subsequent calculation and analysis.Firstly,the battery thermal management system and air conditioning system is coupled,and combined with multi-flow configurations of battery cold plates.The typical series,parallel and hybrid connections are proposed and designed to form a multi-thermaldynamic refrigeration integrated system.The study includes the influence of refrigerant charge,the thermodynamic energy analysis,and comparison and analysis the structural and control characteristics of different system layout.The results show that the change of system layout and load does not influence on the optimal charge of refrigerant.Under the same operating conditions,the COP and exergy efficiency?_ex of the series system,as well as the cooling effect are higher than the parallel system.Considering the priority management,‘short-circuit'temperature control strategies,as the current mainstream connection mode,the parallel system has excellent performance in the cabin temperature response rate,while the series system has excellent performance in the battery temperature control ability and system energy efficiency,which can be used as a choice and reference for the integrated thermal management coupling mode.Based on the study of the coupling correlation in the integrated refrigerant-based thermal management system,the aging characteristics of the battery are further considered to explore its effects on the electric vehicles thermal management system.The study focuses on exploring the uniform distribution of battery thermal and aging parameters,the measures of changing the heat exchange structure and adding equalization strategy to increase the consistency of battery parameters are analyzed.Based on the predetermined basic working conditions,the influence relationship between the thermal management system and the battery aging is analyzed with the periodic change of ambient temperature and the different levels of SOC operating range.Further,from the positive effect of thermal management operation on battery deterioration and the adverse effects of system parasitic energy consumption,the target temperature of battery thermal management is optimized.The results show that when the ambient temperature is within 10?40°C of the battery well working temperature area,the battery control target temperature fluctuates by 1^oC depending on the ambient temperature value to achieve the system energy consumption and the battery aging optimization.Furthermore,a control method of predictive feedforward under the battery life cycle is proposed.The thermal management control implementation is achieved by identifying the battery state parameter SOH_R to update control parameters.The research results provide guidance for formulating the battery life-priority thermal management plan and extending working life.Finally,after completing the structural and thermal characteristics analysis of the key components of the refrigerant-based thermal management system,the design and integration of the system,and the improvement and enrichment of battery aging elements,the overall control and optimization methods of the thermal management system is further designed and explored in the vehicle environment.Through the global sensitivity analysis method based on variance,the sensitivity between the target quantities and the controlled quantities is measured.And the NSGA-?algorithm is used to optimize the driving parameters of the thermal management system.Taking refrigerant-based series and parallel thermal management systems,and typical load conditions as examples,under the action of multi-objective optimization function(the temperature change rate of the controlled component,the instantaneous power of the power battery,the energy consumption of the thermal management system,and the battery aging rate),the basic control mode is analyzed to ensure the temperature level of the controlled component.An optimized comparative analysis of the thermal management system is carried out.The example shows that under the same conditions,the battery aging rate,temperature drop rate and system energy consumption level of the series system are increased by 15.29%,45.23%,and 23.10%compared with the parallel system.The parallel system has4.51%and 50.09%improvement in the cabin temperature drop rate and battery peak power compared with the series system.This means that the series system is conducive to the optimization of battery performance and the long-term energy consumption of the system,and the parallel system is beneficial to the optimization of the cabin comfort and the instantaneous power of the system.The research work in this paper is based on the experiment and simulation of refrigerant-based thermal management of electric vehicles.The content covers performance analysis of battery thermal management circuit to integrated system architecture degisn and exploration,from the new battery state to aging state of the whole life consideration,from the single temperature control to the multi-objective optimization control.The new refrigerant-based thermal management system is systematic explored and studied.The related work is not only forward-looking and innovative,but also lays the foundation and provides guidance for follow-up research and technology application.