Author: Wang, Xiaolin
Title: Cell balancing techniques for electric vehicles and associated distributed mobile energy storage city study
Advisors: Cheng, K. W. Eric (EE)
Degree: Ph.D.
Year: 2018
Subject: Renewable resource integration
Electric vehicles -- Batteries
Storage batteries
Hong Kong Polytechnic University -- Dissertations
Department: Department of Electrical Engineering
Pages: xvii, 110 pages : color illustrations
Language: English
Abstract: Environmental protection has become a global priority as people are getting increasingly aware of the importance of sustainable development. Energy storage system is receiving increasing attention as it can store and buffer power with fast response. Due to the intermittence nature and stochastic user behavior, developing effective storage system is the cornerstone for integration of new energy sources, such as photovoltaic, wind power and electric vehicles (EV). Therefore, this thesis thrives to provide novel control techniques for balancing voltages of hybrid new energy sources and facilitating new energy penetration to increase power efficiency. Distributed energy sources, composed of distributed generation and energy storage, are another type of new energy sources penetrated in smart cities. For energy storage, supercapacitor (SC) has attracted increasing interest as it has advantages in high power density. In future energy storage systems, the types of energy sources will be hybrid for performance optimization which add extra challenges for cell balancing. Based on switched-capacitor and tapped-inductor principles, this thesis puts forward two novel and flexible topologies for balancing of hybrid energy sources which pave ways for the integration of SCs with other existing sources with higher compatibility and balancing accuracy. EVs usually have various driving modes that balancing circuit should also equip energy loss reduction and multi-function capabilities. To overcome the problem of switching loss during balancing process, another novel cell balancing circuit is proposed with integration of zero-current switching technique. Moreover, the balancing circuit proposed can change between buck-boost pattern and switched-capacitor pattern with flexible control to cater the balancing requirements under different driving scenarios. By solving the problem of cell balancing, EVs of high performance can play important roles in improving energy efficiency in smart city. In a combined urban transportation and power grid system, EVs are not only simple transport tools, but also mobile and distributed energy sources/consumers. However, there are mainly three challenges in utilizing energy from EVs: Firstly, the stochasticity of driving behavior, traffic and weather should be taken into account in the forecast of EV charging demand. Secondly, the control strategies adopted for peak shaving among all functioning urban districts shall be redesigned for optimized charging arrangement and energy utilization. Thirdly, the compensation to attract customer control acceptance should be considered as human may arbitrarily not follow control signals. This thesis strives to make a more practical forecast of EV charging demand with Markov chain model and propose an effective pricing control strategy with consideration of EV user behavior for improving the energy efficiency of the city.
Rights: All rights reserved
Access: open access

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