Study of a Symmetrical LLC Dual-Active Bridge Resonant Converter Topology for Battery Storage Systems

A symmetrical LLC resonant converter topology with a fixed-frequency quasi-triple phase-shift modulation method is proposed for battery-powered electric traction systems with extensions to other battery storage systems. Operation of the converter with these methods yields two unique transfer characteristics and is dependent on the switching frequency. The converter exhibits several desirable features: 1) load-independent buck-boost voltage conversion when operated at the low-impedance resonant frequency, allowing for dc-link voltage regulation, zero-voltage switching across a wide load range, and intrinsic load transient resilience; 2) power flow control when operated outside the low-impedance resonance for integrated battery charging; 3) and simple operational mode selection based on needed functionality with only a single control variable per mode. Derivation of the transfer characteristics for three operation cases using exponential Fourier series coefficients is presented. Pre-design evaluation of the S-LLC converter is presented using these analytical methods and corroborated through simulation. Furthermore, the construction of a rapid-prototyping magnetics design tool developed for high-frequency transformer designs inclusive of leakage inductance, which is leveraged to create the magnetic elements needed for this work. Two 2kW prototypes of the proposed topology are constructed to validate the analysis, with one prototype having a transformer incorporating the series resonant inductance and secondary clamp inductance into the transformer leakage and magnetizing inductance, respectively. A test bench is presented to validate the analysis methods and proposed multi-operational control scheme. Theoretical and experimental results are compared, thus demonstrating the feasibility of the new multi-mode operation scheme of the S-LLC converter topology

The use of direct current distribution systems in delivering scalable charging infrastructure for battery electric vehicles

The use of low voltage direct current (LVDC) distribution is becoming recognised as a technology enabler that can be used to efficiently network native DC generators with DC loads, offer improved power sharing capabilities, reduce power system material resource requirements and enhance the performance of variable speed machinery. Practical deployment opportunities for LVDC range from small-scale microgrids in the context of energy for development to sophisticated, modern building-level power distribution systems for commercial office spaces, manufacturing applications and industrial processes. However, the incumbent AC distribution system benefits from existing technical product and safety standards, which makes the early adoption of LVDC systems challenging from a risk and cost perspective. Concurrently, the demand for native DC loads such as Battery Electric Transportation Systems is growing. This is especially significant in the area of private electric vehicles (EVs), taxis and buses, but the prospect of electric trucks, ferries and shortrange aircraft are also tangible opportunities. The success of this electric transport revolution depends on several factors, one of which is the availability of battery charging infrastructure that can cost effectively integrate with the existing electrical network, deliver adequate energy transfer rates and adapt to the rapid technical development of this industry. This thesis explores the application of two, novel LVDC distribution systems for the development of scalable EV charging networks; where charging infrastructure has the ability to scale with increasing EV adoption and has a lower risk of becoming a stranded asset in the future. The modelling is supported by real, rapid DC charger utilisation data from the national charging network in Scotland, comprising over 192 chargers and 400,000 charging events. During the work of this thesis, it was found that a combined heat and power (CHP) system can economically support short duration charging scenarios by providing additional power capacity in a congested electrical grid. In this case the highest system efficiency and Net Present Value (NPV) is achieved with a fuel cell directly connected to the DC charging network, compared to other gas reciprocating CHP options. Furthermore, the proposition of a reconfigurable LVDC charging network, interfaced to the public AC distribution network, reduces the capital outlay, offers a higher NPV and improved scalability compared to other charging solutions. For charging system designers and operators, it was found that rapid DC chargers can be classified by specific locations, each possessing a distinct Gaussian arrival pattern and Gamma distribution for charging energy delivered.The use of low voltage direct current (LVDC) distribution is becoming recognised as a technology enabler that can be used to efficiently network native DC generators with DC loads, offer improved power sharing capabilities, reduce power system material resource requirements and enhance the performance of variable speed machinery. Practical deployment opportunities for LVDC range from small-scale microgrids in the context of energy for development to sophisticated, modern building-level power distribution systems for commercial office spaces, manufacturing applications and industrial processes. However, the incumbent AC distribution system benefits from existing technical product and safety standards, which makes the early adoption of LVDC systems challenging from a risk and cost perspective. Concurrently, the demand for native DC loads such as Battery Electric Transportation Systems is growing. This is especially significant in the area of private electric vehicles (EVs), taxis and buses, but the prospect of electric trucks, ferries and shortrange aircraft are also tangible opportunities. The success of this electric transport revolution depends on several factors, one of which is the availability of battery charging infrastructure that can cost effectively integrate with the existing electrical network, deliver adequate energy transfer rates and adapt to the rapid technical development of this industry. This thesis explores the application of two, novel LVDC distribution systems for the development of scalable EV charging networks; where charging infrastructure has the ability to scale with increasing EV adoption and has a lower risk of becoming a stranded asset in the future. The modelling is supported by real, rapid DC charger utilisation data from the national charging network in Scotland, comprising over 192 chargers and 400,000 charging events. During the work of this thesis, it was found that a combined heat and power (CHP) system can economically support short duration charging scenarios by providing additional power capacity in a congested electrical grid. In this case the highest system efficiency and Net Present Value (NPV) is achieved with a fuel cell directly connected to the DC charging network, compared to other gas reciprocating CHP options. Furthermore, the proposition of a reconfigurable LVDC charging network, interfaced to the public AC distribution network, reduces the capital outlay, offers a higher NPV and improved scalability compared to other charging solutions. For charging system designers and operators, it was found that rapid DC chargers can be classified by specific locations, each possessing a distinct Gaussian arrival pattern and Gamma distribution for charging energy delivered

Comparative study of DC/DC electric vehicle charging system with conventional transformer and planar transformer

This paper presents an analysis of electric vehicle charging station operation based on a dual active bridge topology. Two cases are considered: one with the use of a medium frequency planar transformer, the other with a conventional Litz winding transformer. An analysiswas performed using both solutions in order to compare the performance characteristics of the system for both cases and to present the differences between each transformer solution. The analysis was based on tests carried out on the full-scale model of an electric vehicle charging station, which is the result of the project "Electric vehicle charging system integrated with lighting infrastructure" realized by the Department of Drives and Electrical Machines, Lublin University of Technology. The results presented in the paper show that the conventional transformer used in the research achieved better results than the planar transformer. Based on the results obtained, the validity of using both solutions in electric vehicle charging stations was considered

An Integrated Single-phase On-board Charger

With the growing demand for transportation electrification, plug-in electric vehicles (PEVs), and plug-in hybrid electric vehicles (PHEVs), cumulatively called electric vehicles (EVs) are drawing more and more attention. The on-board charger (OBC), which is the power electronics interface between the power grid and the high voltage traction battery, is an important part for charging EVs. Besides the OBC, every EV is equipped with another separate power unit called the auxiliary power module (APM) to charge the low voltage (LV) auxiliary battery, which supplies all the electronics on car including audio, air conditioner, lights and controllers. The main target of this work is a novel way to integrate both units together to achieve a charger design that is not only capable of bi-directional operation with high efficiency, but also higher gravimetric and volumetric power density, as compared with those of the existing OBCs and APMs combined. To achieve this target, following contributions are made: (i) a three-port integrated DC/DC converter, which combines OBC and APM together through an innovative integration method; (ii) an innovative zero-crossing current spike compensation for interleaved totem pole power factor correction (PFC) and (iii) a new phase-shift based control strategy to achieve a regulated power flow management with minimum circulating losses

Analysis, Design and Control of a Modular Full-Si Converter Concept for Electric Vehicle Ultra-Fast Charging

L'abstract è presente nell'allegato / the abstract is in the attachmen

Power quality improvement utilizing photovoltaic generation connected to a weak grid

Microgrid research and development in the past decades have been one of the most popular topics. Similarly, the photovoltaic generation has been surging among renewable generation in the past few years, thanks to the availability, affordability, technology maturity of the PV panels and the PV inverter in the general market. Unfortunately, quite often, the PV installations are connected to weak grids and may have been considered as the culprit of poor power quality affecting other loads in particular sensitive loads connected to the same point of common coupling (PCC). This paper is intended to demystify the renewable generation, and turns the negative perception into positive revelation of the superiority of PV generation to the power quality improvement in a microgrid system. The main objective of this work is to develop a control method for the PV inverter so that the power quality at the PCC will be improved under various disturbances. The method is to control the reactive current based on utilizing the grid current to counteract the negative impact of the disturbances. The proposed control method is verified in PSIM platform. Promising results have been obtaine

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Department of Electrical EngineeringA resonant converter has been widely used in various industrial applications, since it has high power conversion efficiency. The increase of the power density is necessary to obtain high cost-effectiveness and design freedom on the electric products. A high switching frequency operation can be an effective method to obtain the high power density of power converters. In this dissertation, three topic will be discussed to obtain the high power conversion efficiency and the high power density for the resonant converter, as follows: First, the power stage and feedback loop are designed for the high switching frequency operation. The power stage is designed to obtain the high power conversion efficiency at the high switching frequency operation. In addition, the feedback loop is designed to guarantee the stability. Second, the control algorithm is proposed to obtain the tight output voltage regulation at the high switching frequency operation. The operational principle and design of control algorithm are analyzed to obtain the tight output voltage regulation. Third, the spread spectrum technique (SST) will be applied to the resonant converter to reduce the electromagnetic interference (EMI), which can improve the power density with small EMI filter size. In this research, the design constraint to implement the SST on the resonant converter is analyzed to obtain the dual functionality properly. In addition, the control algorithms are proposed to achieve tight output voltage regulation and EMI reduction, simultaneously. All the proposed design considerations and control algorithms are verified with the simulation and experimental results.clos

High Power Capacitive Power Transfer for Electric Vehicle Charging Applications

Capacitive power transfer (CPT) technology is an effective way to charge electric vehicles, in which electric fields between metal plates are used to transfer power. Compared to the conventional inductive power transfer (IPT) system, a CPT system has three advantages: it does not generate eddy-current loss in nearby metal objects; it can reduce the system weight and cost; it has better misalignment performance. However, the coupling capacitance in a CPT system is usually in the pF range, which limits the CPT system power and efficiency. Through overcoming the limitation of small capacitance in a CPT system, this dissertation has achieved three breakthroughs in CPT technology: the system power is increased from several tens of watts to several kW; the transfer distance is increased from less than 1 mm to hundreds of mm; the transfer efficiency is increased from about 30% to over 90%. A double-sided LCLC compensation circuit has been proposed to realize high-power and long-distance capacitive power transfer. The compensation circuit provides resonances with the coupling capacitance, and increases the voltages on metal plates to kV level to achieve kW power transfer. A prototype has been constructed and validates the proposed circuit. Experimental results show that the prototype realizes 2.4 kW power transfer across an air-gap distance of 150 mm with a dc-dc efficiency of 90.8%. The experiments also show that the CPT system has better misalignment performance than the conventional IPT system. An IPT-CPT combined system has also been proposed to integrate the IPT and CPT technology together. The combination can increase the efficiency of the CPT system, and improve the misalignment performance of the IPT system. A prototype has been constructed to validate the combined idea. Experimental results show that the prototype realizes 2.84 kW power transfer across an air-gap distance of 150 mm with a dc-dc efficiency of 94.4%. Using the designed LCLC compensation circuit, a dynamic CPT system has been proposed to realize power transfer to receivers in moving status. A long-track coupler structure is used to reduce the pulsation of received power. A prototype has been constructed to validate dynamic charging. Experimental results show that the prototype realizes 154W power transfer across an air-gap distance of 50 mm with a dc-dc efficiency of 85.4%. Considering practical applications, the safety issues and foreign object influence have been studied in this dissertation. The high voltage issue can be solved by reliable insulation, and the electric field emissions can be reduced through capacitive coupler structure design. The foreign object, either metallic or dielectric, can influence the coupling capacitances in a CPT system depends on the position and size. The CPT system can also influence the voltage and power loss in the foreign object. To sum up, this dissertation has demonstrated that the CPT technology is a good solution to realize the charging of electric vehicles. In future work, the power density and efficiency of the CPT system will be further improved to make it more competitive with the inductive and conductive charging technology.PHDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138493/1/feilu_1.pd