Sinusoidal Charging Scheme And Battery Management System For Lithium-ion Batteries

With the increase of the car ownership in the world year by year,the energy and environment issues caused by the traditional fuel vehicles become increasingly serious.Correspondingly,electrical vehicles whose energy is provided by batteries have been developed rapidly.Different from the traditional fuel vehicles,the batteries in the electrical vehicles need to be charged by an on-board battery charger,and hence the safety of the batteries is closely related to the performance of the charger.The capacity of one battery cell is usually small and the batteries need to be series or parallel connected for larger capacity to meet the requirement of the vehicle.In order to guarantee the safety of hundreds of battery cells,the battery management system is installed to monitor batteries status.Consequently,the research on the on-board battery charger and the battery management system is carried out in this thesis.The electrolytic capacitor is often used on the dc link of the battery charger,whose volume is large and lifetime is short.In order to solve this problem,this paper proposes a lithium-ion battery sinusoidal charging scheme,with which the dc link capacitors need not to compensate the power imbalance any more and hence the capacitance can be much reduced.A LLC dc-dc transformer based charger topology is seleced for this sinusoidal charging scheme.The design of the resonant parameters is optimized.Moreover,a sinusoidal power decoupling control is proposed to achieve the sinusoidal charging.The small signal modeling of the proposed control is introduced to design the controller.On the other hand,this thesis introduces the fundamental functions of the battery management system.The difference between the centralized structures and the distributed structures has been discussed.Moreover,the advantages and disadvantages of the prior art solution are both researched,including the battery voltage sampling,battery balancing and digital signal controller software design,providing the refercence for the design of the battery management system.In order to verify the feasibility of the proposed LLC DCX battery charger solution with the sinusoidal charging scheme,a 1 kW scaled-down battery charger prototype has been built.The sinusoidal charging current is achieved and the efficiency of the charger maintains above 95.8% during the whole charging process.A distributed structure based battery management system is designed for a high voltage electrical vehivle.The prototype together with the test platform is provided.The experimental results verify the protection ability of the battery management system for the lithium-ion batteries.