| In response to the shortage of fossil energy and environmental pollution,hybrid electric vehicles(HEVs)have become one of the major solutions to energy saving and emission reduction in transportation section.However,since the concept of HEV was first proposed in 1971,although enormous HEVs have been designed and manufactured,there has not yet been generic and uniform design theories or engineering regulations for solving the design problem on HEV powertrains that reflect the major technical characteristics of the HEV.Thus,in the planning and developing stage of HEV powertrain design,the design task has been frequently challenged by following practical issues.For the given vehicle parameters,what kind of HEV powertrain architectures can be considered?What are the alternative architectures?Will different types of HEV architectures have specific technical requirements or preferences for the characteristics of their components?How could these architectures be compared and evaluated;in addition,how could the optimal system design scheme composed of architecture and component parameters be distinguished and selected among all possible system design schemes?Whether there is a new architecture leading to a novel HEV powertrain design that surpasses the existing HEV powertrain design schemes in certain performance?Or whether there could be a new architecture and its corresponding HEV powertrain design that could provide a larger trade-off range of different performances and satisfy more consumers?In fact,the series of problems mentioned above can be formulated as a system optimization problem,which is to search for the solution(system design scheme)that enables the objective function to take its optimum value within a given design domain.However,the architecture of the HEV powertrain is defined in topological concept rather traditional real number.As the key scientific issues to be solved in this dissertation,incorporating the system architecture in topological concepts into traditional optimization theory inevitably triggers the following mathematic problems:How could the integrated influences of system control strategy,component parameters and configuration schemes on performance of HEV powertrain be decoupled?Further,are there quantitative parameters that can be utilized for evaluating the HEV design schemes so as to provide the searching and evaluation rules for the mathematical optimization design model?How could design constraints for the architectures of HEV powertrains be established in topological space,and thus how the unified mathematical method that could provide the unified representation for the feasible design domain of generic types of architectures of HEV powertrains could be developed?Is it possible to establish a correlated mapping describing the topology of the architecture of the HEV powertrains in the domain of real number,so that the optimization algorithm can simultaneously conduct optimization operations on the architecture selection and component sizing for the HEV powertrain in the domain of real number,which in mathematical theory guarantees the optimality of design results?It is expected to offer a theoretical method or direct solutions to these practical engineering problems mentioned in the beginning by solving these mathematic problems above.As the academic achievements of this dissertation,the optimal performance of an HEV powertrain design scheme is selected as the quantitative indicator for the evaluation of the HEV powertrain design schemes.Additionally,to formulate a mathematic model for solving the architecture selection and component sizing,the control strategy,component parameter and architecture integrated optimization method is developed by utilizing the nested optimization strategy.Further,to provide the design domain of architecture for the mathematic optimization model of HEV powertrain system,a graph representation model for describing generic types of HEV powertrain architectures is deduced and developed according to the common features of power coupling and transmission patterns in different types of HEV powertrain architectures.Compared with the existing or traditional graph representation model,the generic graph representation model proposed in this dissertation provides a complete candidate set(design domain)of HEV powertrain architectures for system optimization,and the restriction imposed by the specific mechanism or architectures on domain exploration of optimization can be avoided.Therefore,the optimality of the design results can be guaranteed.On basis of the generic graph representation model,utilizing the system kinematic matrix as the representation of architecture schemes in the domain of real number,the topology-to-real number bijection is developed,which enables the optimization algorithms to conduct the searching operation on architecture and component parameters simultaneously in the domain of real number and supports reconstructing the topologic structure of HEV powertrain architecture according to the numeric design results.For the generation problem of complex architecture schemes,a new constraint propagation(constrained programming)algorithm is proposed and tested in this dissertation,which aims to improve the calculation efficiency of the automatic generation of complex architecture schemes.This improvement in computational efficiency provides the technical support for the integrated optimization method proposed in this dissertation and extends the application scope of the integrated optimization method to more complex design tasks.The research work leading to the achievements above includes:(1)Considering the representative design objectives simultaneously,such as energy economy and acceleration capability,the optimal performance of an arbitrary design schemes of HEV powertrain system is extracted by the global optimization control strategy,and the optimal performance is used as a quantitative indicator for evaluating the system design schemes of HEV powertrain.Therefore,the influence of control strategy on system performance is decoupled.(2)Considering the restriction of architecture,component parameters and control strategy on the optimal performance of the HEV powertrain system,the control strategy,component parameter and architecture integrated multi-objective optimization method is proposed and developed by adopting the nested optimization strategy.In the nested optimization algorithm,the control strategy of an arbitrary HEV powertrain design is optimized in the inner layer in order to extract its optimal performance as evaluation indicator,while the outer layer of the nested optimization algorithm further modifies the optimal performance of the given HEV powertrain by optimization of the component parameters of the HEV powertrain.Therefore,the influence of component parameters on system performance is decoupled,and the criterion of architecture selection can be quantified by the result of the nested optimization.Further,on basis of this endeavor,the comprehensive searching pattern for optimal design schemes and basic mathematic model for solving the system optimization are established.(3)The common functional features of different types of HEV powertrain architectures are summarized according to their power coupling and transmission patterns.Additionally,the graph representation model for describing generic types of HEV powertrain architectures is developed based on the fundamental elements that makes up the topology structures of HEV powertrains.Thus,the graph representation model is freed from the restriction of specific mechanism or architecture of HEV powertrain,and,in topological space(domain),the graph representation model could prepare the complete design domain of architectures for the mathematic optimization model of HEV powertrain system.The system kinematic matrix is extracted and utilized as a representation of HEV architecture in the space of real number,which provides the topology-to-real number mapping for the graph representation model.This achievement bridges up the gap between topological structure and system mathematic information and ensures that optimization algorithms could operate on both architecture selection and component sizing simultaneously in the domain of real number.(4)Supported by the topology-to-real number mapping,the control strategy,component parameter,and architecture integrated multi-objective optimization method is expanded and improved by adding the architecture design variable that is converted into the domain of real number,and therefore the Pareto optimal design schemes of HEV powertrains involving generic types of architectures are obtained by the proposed integrated optimization method.Further,to correctly reconstruct the topology of the HEV powertrain according to the optimization results in the domain of real number,a fast topology reconstruction algorithm is engineered,which finally leads to the topology-to-real number bijection.(5)For solving the generation problem of large-scale(complex)HEV powertrain architectures,based on the logical representation of topological structure(vertices and edges),a mathematical model of constraint programming is developed,and all possible architectures are constructed by accumulating all feasible sub-topologies.Therefore,the constraint programming mothod realizes dimensionality reduction and computational efficiency improving compared with the traditional enumeration method.Additionally,the correlation between variables and constraints is discovered through the analysis of the topological meaning of variables and design constraints,and a grouped ordering search strategy is proposed based on this,which further improves the computational efficiency of solving the generation problem of large-scale architectures.In this dissertation,the innovative research work and results on the architecture representation model,multi-objective performance evaluation and optimization method for hybrid powertrain system design support the major theoretical research work of the research program‘system architecture optimization and dynamic control method for plug-in/range-extend HEV powertrains'in National Key R&D Program of the 13thFive-Year Plan of the Ministry of Science and Technology... |
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