AC-DC PFC Converter Using Combination of Flyback Converter and Full-bridge DC-DC Converter

This paper presents a combination of power factor correction converter using Flyback converter and Full-bridge dc-dc converter in series connection. Flyback converter is operated in discontinuous conduction mode so that it can serve as a power factor correction converter and meanwhile Full-bridge dc-dc converter is used for dc regulator. This converter system is designed to produce a 86 Volt of output voltage and 2 A of output current. Both simulation and experiment results show that the power factor of this converter achieves up to 0.99 and meets harmonic standard of IEC61000-3-2.Keywords: Flyback Converter, Full-bridge DC-DC Converter, Power Factor Correction

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

Single-Stage Power Electronic Converters with Combined Voltage Step-Up/Step-Down Capability

Power electronic converters are typically either step-down converters that take an input voltage and produce an output voltage of low amplitude or step-up converters that take an input voltage and produce an output voltage of higher amplitude. There are, however, applications where a converter that can step-up voltage or step-down voltage can be very useful, such as in applications where a converter needs to operate under a wide range of input and output voltage conditions such as a grid-connected solar inverter. Such converters, however, are not as common as converters that can only step down or step up voltage because most applications require converters that need to only step down voltage or only step up voltage and such converters have better performance within a limited voltage range than do converters that are designed for very wide voltage ranges. Nonetheless, there are applications where converters with step-down and step-up capability can be used advantageously. The main objectives of this thesis are to propose new power electronic converters that can step up voltage and step down voltage and to investigate their characteristics. This will be done for two specific converter types: AC/DC single-stage converters and DC-AC inverters. In this thesis, two new AC/DC single-stage converters and a new three-phase converter are proposed and their operation and steady-state characteristics are examined in detail. The feasibility of each new converter is confirmed with results obtained from an experimental prototype and the feasibility of a control method for the inverter is confirmed with simulation work using commercially available software such as MATLAB and PSIM

DC-DC and AC-DC Converters Based on Three-Phase DC-DC Topologies

Power electronics is the field of electrical engineering that uses power semiconductor devices along with passive elements such as inductors, capacitor and transistors to convert electrical power that can be generated by a source to a form that is suitable for user loads. The main focus of this thesis is on the development of new DC-DC and AC-DC topologies that are based on three-phase DC-DC converters. Three-phase DC-DC converters take an input DC voltage, convert it into a high-frequency AC voltage that is then stepped up or down, then rectify and filter this voltage to produce an output DC voltage. They are implemented with a high-frequency three-phase transformer in their topology rather than a single-phase transformer. These converters are very attractive over other topologies that have a single-phase transformer in their topologies for several reasons. First, just one three-phase DC-DC converter can be used instead of using three DC-DC converters in parallel for particular applications; this advantage is especially attractive for higher power applications. In addition, by using three-phase DC-DC converters, the ripple of the source current is significantly reduced and that means less filtering is needed. Moreover, the components of the converter will have less current stress because current is split among three-phases. In this thesis, new DC-DC and AC-DC converters that are based on three-phase DC-DC topology are proposed. The proposed converters use fewer active switches than other previously proposed converters of similar type, thus resulting in lower cost and simpler operation. For each of the proposed converters, its steady-state characteristics are determined by mathematical analysis and procedure for the design of key converter components is developed. The feasibility of each proposed converter has been confirmed with results that have been obtained from experimental prototypes. For one of the proposed converters, a comparison between the operation of one of the proposed converters operating with traditional silicon devices (Si) and that with the converter operating with new silicon-carbide devices (SiC) was made to examine its performance with both types of devices

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