Battery charging system incorporating an equalisation circuit for electric vehicles

Ph.D. ThesisHybrid electric vehicles (HEVs) and electric vehicles (EVs) are gaining in popularity mainly due to the fact that unlike combustion-powered vehicles, they do not pollute with greenhouse gases and toxic particles. Most HEVs and EVs are powered by lithium-ion battery packs which have high power density and longer cycle lives compared to other battery types. Each pack is made out of many battery cells in series connected and due to manufacturing tolerances and chemical processes in individual cells each cell has its own electric characteristics. In order to achieve a balanced voltage across all cells, a battery management system (BMS) must be employed to actively monitor and balance the cells voltage. On-board battery chargers are installed in HEVs/EVs to charge the lithium-ion battery pack from the grid. This charger converts AC grid voltage into a controllable DC output voltage, but it adds weight to the vehicle, reducing the overall efficiency of an HEV/EV and also increasing its cost. The aim of researches in multi-functional power electronics is to design systems which perform several different functions at the same time. These systems promise cost and weight reductions since only one circuit is used to conduct different functions. An example is the electric drive in an HEV/EV. On one hand, it propels the car forward when driving, while on the other hand the battery can be charged via a modified electric motor and inverter topology. Thus, no additional on-board charger is required. This thesis describes a new multi-functional circuit for HEVs/EVs which combines the functions of voltage equalisation with grid charging. Compared to a drive system, the proposed circuit does not rely on an electric motor to charge the battery. Various battery chargers and equalisation circuits are first compared. Then, the design of the proposed circuit is described and simulation results are presented for charging and voltage balancing. An experimental test rig was built and practical results have been captured and compared with simulation results for validation. The advantages and disadvantages of the proposed circuit are discussed at the end of the thesis. Keywords- Multi-functional system, Battery charging, Voltage equalisation, Lithium-ion batter

A ripple reduction method for a two stages battery charger with multi-winding transformer using notch filter

This paper presents a two-stage battery charger consisting of a bridgeless Totem-pole power factor correction (TP-PFC) circuit and a full bridge converter with a multi-winding transformer. By using this transformer the cell equalizing operation can be achieved with no additional circuitry. In addition, a double-line frequency ripple reduction method is proposed to address the low frequency current ripples issues existing in both primary and secondary winding of the transformer which is caused by the voltage ripples across the intermediate DC link bus. Control and analysis of the converter at different operation modes is illustrated in detail and simulation results validate the effectiveness of the proposed converter and control algorithm

Combining electric vehicle battery charging and battery cell equalisation in one circuit

Electric vehicles (EVs) require an onboard battery charger unit and a battery management system (BMS) unit that balances the voltage levels for each battery cell. So far both units are two completely autarkic power electronics systems. This paper presents a circuit that operates as a battery charger when the EV is connected to the grid and as a voltage balancer when the EV is driving. Thus, the proposed circuit utilises two functions in one and therefore eliminates the need of having two autarkic units reducing complexity and reduction in component count. The proposed circuit operates as a flyback converter and achieves power factor correction during battery charging. The constant-current constant-voltage (CC–CV) charging method is employed to charge the batteries. However, to limit the number of sensors that will be employed as a result of varying cells during charging, the battery current is estimated using a single current transducer and embedding a converter model in the controller. The operation of the circuit is presented in detail and is supported by simulation results. A laboratory prototype is built to verify the effectiveness of the proposed topology. Experiment results show that the proposed method provides an integrated solution of on-board charging and voltage equalisation

Content Sharing in a Social Broadcasting Environment: Evidence from Twitter

The rise of social broadcasting technologies has greatly facilitated open access to information worldwide, not only by powering decentralized information production and consumption, but also by expediting information diffusion through social interactions like content sharing. Voluntary information sharing by users in the context of Twitter, the predominant social broadcasting site, is studied by modeling both the technology and user behavior. A detailed data set about the official content-sharing function on Twitter, called retweet, is collected and the statistical relationships between users’ social network characteristics and their retweeting acts are documented. A two-stage consumption-sharing model is then estimated using the conditional maximum likelihood estimatio (MLE) method. The empirical results convincingly support our hypothesis that weak ties (in the form of unidirectional links) are more likely to engage in the social exchange process of content sharing. Specifically, we find that after a median quality tweet (as defined in the sample) is consumed, the likelihood that a unidirectional follower will retweet is 3.1 percentage point higher than the likelihood that a bidirectional follower will do so

Por la dignidad arzobispal de Toledo, y demàs participes, en los diezmos de su Arçobispado. En los pleytos que a su instancia de Don Juan Saenz de Vitoria, y D. Francisco Diaz de la Puebla ... : Sobre a quien toca el conocer ...

Texto escrito por el Licenciado D. Pedro Gomez de la CabaEn h. 3 consta: "el año passado de 696 [i.e. 1696] ..."Sign.: A-K\p2\s, L\p1\sPort. con orla ti

The exploration of flow pattern in the superior vena cava of healthy adults: A 4D flow magnetic resonance imaging study

Our study sought to investigate the blood flow pattern in the superior vena cava (SVC) of healthy adults and to describe the development and characteristics of the flow pattern using 4D flow magnetic resonance imaging (MRI). 4D flow MRI data with full coverage of SVC and brachiocephalic veins (BVs) were acquired with a 3-Testa MRI in thirty healthy adults (age: 28.70 ​± ​9.09). Hemodynamic parameters in the SVC, including velocity, velocity vector, flow visualization (pathlines, streamlines), flow waveform and energy loss, were obtained with specialized commercial post-processing software based on 4D flow MRI data. This study found that: (1) The SVC has a pulsating flow waveform with double peaks. (2) Based on BVs flow of the SVC pathline visualization, flow patterns could be divided into three development types: twining (n ​= ​14), untwining (n ​= ​9) and no helical flow (n ​= ​7). (3) With the decreasing blood velocity, helical flow areas tended to gradually extend. (4) There were no significant differences in most hemodynamic parameters among the three types. The exploration of the blood flow characteristics of normal SVC may be the first step for capturing pathogenic features before the patients develop symptoms with a certain positive significance. The potential physiological significance of these phenomena deserves more exploration in future studies