DC Fast Charging Research Articles

Determining the optimal electric vehicle DC-charging infrastructure for Western Australia

Take-up rates of electric vehicles (EV) are increasing and are predicted to accelerate rapidly. Public EV charging networks will be required to support future EV fleets. If unplanned, public charging networks are highly likely to be suboptimal. Planners need to understand and plan for future EV charging infrastructure requirements, particularly public DC fast charging networks, as both the upfront investment costs and the consequences of misallocation are high. However, the task of determining the optimal locations and allocations (types and numbers) of public EV charging infrastructure is complicated as it requires knowledge of many variables. These include EV driver behaviors, driving patterns, predicting evolutionary changes in EV and EV charging technologies, future EV take-up rates, and what investment may or may not occur in the absence of government funding support.

Lifetime Optimization for a Grid-Friendly DC Fast Charge Station With Second Life Batteries

Abstract Electrified vehicle (EV) batteries that have reached the automotive end of life are providing a low-cost energy storage solution for grid-connected systems, such as DC fast charge stations (DCFCs). There are several challenges associated with the integration of second life batteries (SLBs) in power systems, such as the definition of a systematic approach for the concurrent optimization of performance and lifetime with the aim of minimizing the investment and operating costs. This paper proposes the application of automotive SLBs to DCFC stations where high-power grid connection is not available or feasible. The SLBs are charged using a low-power grid connection and then provide DCFC power to the EVs. An optimal control problem has been formulated to identify the energy management control (EMC) strategy that allows minimizing the replacement rate of the SLBs, while ensuring the EV load request is match.

A Control Approach Integrating Electric Vehicle Charger and Dynamic Response of Demand-Side Resource Aggregators

Regardless of whether level 1, level 2, or dc fast charging, several methods are under development or available as an aftermarket option for Plug-in electric vehicles (EVs). While confining the charging behavior of EVs to low-load periods is difficult, it leads to significant and uncertain load peaks and valleys in the utility power network. Therefore, this paper proposes a new method for an electric vehicle charger. The proposed charging method involves power supervisory characteristics on the basis of the paradigm of a constant-current and a constant-voltage (CC–CV) charger so that the external commands from the demand-side resource aggregator in the smart grid can be executed. In the method, first, a feedback loop is included in the controller to formulate the relationship between battery voltage and charging power as a quadratic concave downward polynomial. The controlled output power at the beginning of constant voltage charging is then set to the maximum value of the quadratic polynomial because the charging power requirement near this point is closed to the highest. Hence, if the charging power is lower than the allowable maximum power, the proposed charger is determined to have followed the traditional CC–CV charging steps. On contrast, the proposed circuit launches the power control loop when the actual charging power is beyond the maximum power limitation of aggregator. The proposed charger can keep the power consumption inside an allowable range of aggregator. That is the power consumption at the EV charging sites becomes directly programmable by their aggregators. The proposed method is examined by conducting an interactive test of a remote energy management system and the proposed controller. The results revealed that the proposed method provide an easy method to dynamically control consumption pattern of the EV charging for demand-side power management.

Exploring electric vehicle charging patterns: Mixed usage of charging infrastructure

This paper examines the charging behavior of 7,979 plug-in electric vehicle (PEV) owners in California. The study investigates where people charge be it at home, at work, or at public location, and the level of charging they use including level 1, level 2, or DC fast charging. While plug-in behavior can differ among PEV owners based on their travel patterns, preferences, and access to infrastructure studies often make generalizations about charging behavior. In this study, we explore differences in charging behavior among different types of PEV owners based on their use of charging locations and levels, we then identify factors associated with PEV owner’s choice of charging location and charging level. We identified socio-demographic (gender and age), vehicle characteristics, commute behavior, and workplace charging availability as significant factors related to the choice of charging location.

Control Strategies and Economic Analysis of an LTO Battery Energy Storage System for AGC Ancillary Service

With the rapid growth of renewable energy and the DC fast charge pile of the electric vehicle, their inherent volatility and randomness increase a power system’s unbalance of instantaneous power. The need for power grid frequency regulation is increasing. The energy storage system (ESS) can be used to assist the thermal power unit so that a better frequency regulation result is obtained without changing the original operating mode of the unit. In this paper, a set of different charging/discharging control strategies of the lithium titanate battery (LTO) is proposed, which are chosen according to the interval of the State of energy (SOE) to improve the utilization rate of the ESS. Finally, the cost-benefit model of the ESS participating in automatic generation control ancillary service is established. Case analysis proves that after a 1.75 MWh ESS is configured for a 600 MW thermal power unit, Kp and D is increased from 1.42 to 6.38 and 2857 to 6895 MW. The net daily income is increased from 20,284 yuan to 199,900 yuan with a repayment period of 93 days. The results show that the control strategies and the energy configuration method can improve the performance and economic return of the system.

Power factor corrected level‐1 DC public green‐charging infrastructure to promote e‐mobility in India

With the growing popularity of electrified transportation across the world, there have been extensive reports of research involving plug-in electric vehicles (PEVs), electric vehicle charging facilities (EVCFs) and their integration to the main electric grid, besides sustainable energy resources for powering these vehicles. This study proffers a power factor corrected level-1 DC public green-charging infrastructure accompanied by an integrated control, for electric light motor vehicles, compliant with recently formulated Indian charging standards. Power factor correction of plug-in electric vehicle charging current, solar photo-voltaic grid integration and charging of energy storage system is achieved using control of bidirectional AC/DC converters. A firmware and user interface for multimode off-board DC charging, with green, fast and semi-fast charging modes are investigated. Intelligent control for fast charging is also presented to reduce its pernicious impact on the grid. The simulation and hardware results verify the prime performance objectives of improving the local power quality and renewable energy utilisation with multimode charging, in the Indian context. The effectiveness of the proposed infrastructure is further demonstrated by a simulated use case, where 30 PEVs are randomly charged, in various modes, at this EVCF during busy commute hours.

Modeling and Control of Three-Level Boost Rectifier Based Medium-Voltage Solid-State Transformer for DC Fast Charger Application

This paper presents modeling, control, and system design of three-level boost (TLB) rectifier based medium-voltage (MV) solid-state transformer (SST) for dc fast charger application. In order to operate at MV with 1.2-kV SiC devices, the target system is configured by input-series output-parallel (ISOP) multimodule structure. Each module adopts TLB to front-end rectifier and stacked half-bridge LLCs to back-end isolated dc–dc converters. Operation principles of TLB rectifier and LLC converters are analyzed to derive an equivalent model of the entire system. Based on the detailed derivation, this paper aims to achieve three performance criteria, including bus voltage regulation, input current regulation, and voltage balancing. Basic feedback control loops are designed to control TLB’s output voltage and input current in an average manner, based on the derived system model. Then, ideal TLB duty-ratios in both continuous/discontinuous conduction modes are analyzed and duty-ratio feedforward control is proposed to improve the low quality of input current due to inherent feedback control limitations. For voltage balancing, system design approaches are used in the SST prototype. With the proposed control and system design, a prototype of four-module-stacked TLB SST was built and tested up to 3.8-kVrms and 16-kW conditions.

A Drivetrain Integrated DC Fast Charger With Buck and Boost Functionality and Simultaneous Drive/Charge Capability

Electric vehicles have the potential to change the global driving paradigm, significantly reducing the environmental impact of transportation systems. However, charging infrastructure cost and range anxiety impose challenges on rapid technology adoption. This paper proposes an onboard integrated dc charger, leveraging the traction inverter, and motor winding inductance to ensure the minimum incremental mass. The proposed circuit allows the vehicle to connect directly to emerging dc microgrids, utility storage, or renewable energy resources. The system is compatible with power supply voltages higher or lower than the vehicle battery, offering the possibility to charge 400-V batteries from emerging 1000-V supplies, as well as 800-V battery from the existing 600-V dc interfaces. The presented method also provides bidirectional fault blocking capability and bidirectional power transfer, suitable for V2G, G2V, or V2V operation. In addition, this paper proposes simultaneous driving and charging, especially useful for semitrailer trucks applications, significantly increasing operational range. The solution presented in this paper offers a simple and safe charging scheme with the potential to substantially reduce charging infrastructure cost and address range anxiety.

An Output Ripple-Free Fast Charger for Electric Vehicles Based on Grid-Tied Modular Three-Phase Interleaved Converters

An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide ripple-free output current in the typical EV batteries voltage range is presented in this article. The proposed configuration is based on modular three-phase interleaved converters and supplied by the low-voltage ac grid. The ac/dc interleaved three-phase active rectifier is composed of three standard two-level three-phase converter modules with a possibility to slightly adjust the dc-link voltage level in order to null the output current ripple. A modular interleaved dc/dc converter, formed by the same three-phase converter modules connected in parallel, is used as an interface between the dc link and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated as well, considering both possible coupling implementations, i.e., inverse and direct coupling. Numerical simulations are reported to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, including the proposed control strategy aimed to null the ripple of the output current. Experimental results are provided by a reduced scale prototype of the output stage to verify the ripple-free output current operation capability.

An Efficient Energy Management Approach for a Solar-Powered EV Battery Charging Facility to Support Distribution Grids

The home photovoltaic (HPV) system integrated with energy storages can supply power to the distribution grid which may be reliable and free from HPV intermittency effects. However, this is always associated with the high cost of energy storages. On the other hand, the growth of electric vehicles (EVs) in the market has a potential to place the distribution grid in a high risk as the EV owners may charge the EV battery on demand which may cause an unexpected increase in the evening and power quality problems. This article proposes an efficient energy management approach for the HPV systems to power the electric vehicle battery (EVB) charging facility while utilizing the EVB as an energy storage system (ESS) that can mitigate the HPV impacts and allow the growth of HPV systems in power grids. This research is aimed for EVs that are compatible with the dc fast charging CHAdeMO standard. The operation strategy of the HPV-EVB charging system is designed in such a way that the EVB is charged efficiently either by the HPV or by the distribution grid. The proposed energy management strategy will help reduce the unexpected peak power demand, and can help in the implementation of the vehicle-to-grid (V2G) to improve the stability of the grid during peak load. In addition, the EVB can provide power to the critical loads in the home when there is a loss of power supply from the grid. In the proposed system, the HPV, the grid, and the EVB converters share a common dc bus. Both simulation and experimental results show that the proposed energy management of the HPV-EVB system can reduce the impacts of the high penetration of EVs and HPVs on power distribution grids and can effectively improve the self-consumption of the HPV systems.

Extreme Fast Charging Technology—Prospects to Enhance Sustainable Electric Transportation

With the growing fleet of a new generation electric vehicles (EVs), it is essential to develop an adequate high power charging infrastructure that can mimic conventional gasoline fuel stations. Therefore, much research attention must be focused on the development of off-board DC fast chargers which can quickly replenish the charge in an EV battery. However, use of the service transformer in the existing fast charging architecture adds to the system cost, size and complicates the installation process while directly connected to medium-voltage (MV) line. With continual improvements in power electronics and magnetics, solid state transformer (SST) technology can be adopted to enhance power density and efficiency of the system. This paper aims to review the current state of the art architectures and challenges of fast charging infrastructure using SST technology while directly connected to the MV line. Finally, this paper discusses technical considerations, challenges and introduces future research possibilities.

Design and Sizing of Mobile Solar Photovoltaic Power Plant to Support Rapid Charging for Electric Vehicles

Existing DC fast-charging stations are experiencing power quality issues such as high harmonics in the line current, poor power factor in the input supply, and overloading of distribution transformers, due to the dynamic behavior of charging patterns when it is connected to the power grid. Most of the recent works involve the usage of renewable energy sources to mitigate the issues on the distribution grid. In order to design a mobile plug and play DC fast charging station, solar energy is the best and viable solution to carry out. In this paper, plug and play solar photovoltaic power plant to charge electric vehicles (EVs) is proposed and modelled using MATLAB/Simulink software. The proposed system can act as a mobile power plant. The controller allows the system to charge the battery, whenever there is abundant solar energy. Incoming EVs will be charged directly from the system battery where the charger acts as a rapid charging system. The proposed system can meet the concept of Solar Photovoltaic Rapid Charging Stations (SPRCS), which shows that 80% of charge can be fed to an EV in 10.25 min.

Design of 2kW DC Charger for Two Wheelers

The demand for Electric Vehicles is increasing day by day. EVs are silent, nonpolluting and produce zero emissions. This paper presents the design of a dc charger that performs the necessary functions for charging EV battery. An EV charger is a component in EV environment that supplies power for recharging the EV battery. Usually, charging an electric car seems to be very simple process, implying that one can plug one’s car into a charger that is connected to the electric grid. However, it is not as that simple. It depends on the types of EVSE that one has deployed. Offboard DC Charger is connected to the premises wiring of the mains ac supply network .It is designed to be separate and operate entirely off the vehicle. In the offboard dc charger, direct current electrical power is delivered directly to the vehicle. The power module in a DC fast charger consists of an AC-to-DC rectifier converter and an isolated DC/DC converter. The AC-to-DC rectifier is power factor correction stage in which a Vienna Rectifier based PFC converter is used. The Isolated DC-DC Converter used here is the Phase Shift Full Bridge DC-DC converter. A 2 kW prototype of the offboard DC Charger is designed and simulated in MATLAB/Simulink R2018b.

Maintaining a Constant Charging Duration Independent of Battery Capacity for Battery Pack by Designing a Fast DC Charger

This article proposes a novel strategy for developing a new structure for a lithium-ion battery pack fast charger which aims to achieve fast DC charging, based on the topology of a boost converter. The proposed charger has been designed considering using fewer electronic components at lower cost. Varying initial charging percentage of the Li-ion cells has not been addressed in this article, an equal initial charging percentage of each Li-ion cell is assumed. Performance of the proposed structure of the charger has been tested using a simulation environment. This strategy has shown that this structure ensures scalability of this charger, while using the utility grid (220V, 50Hz) as a main power source for this charger has ensured practical usage flexibility. The results of this research are presented and discussed. These results have shown the outstanding performance and response of this charger.

Technology solutions to mitigate electricity cost for electric vehicle DC fast charging

Widespread adoption of alternative fuel vehicles is being hindered by high vehicle costs and refueling or range limitations. For plug-in electric vehicles, direct-current fast charging (DCFC) is proposed as a solution to support long-distance travel and relieve range anxiety. However, DCFC has also been shown to be potentially more expensive compared to residential or workplace charging. In particular, electricity demand charges can significantly impact electricity cost for fast charging applications. Here we explore technological solutions that can help reduce the electricity cost for electric vehicle fast charging. In particular, we consider thousands of electricity rates available in the United States and real-world vehicle charging load scenarios to assess opportunities to reduce the cost of DCFC by deploying solar photovoltaics (PV) panels and energy storage (battery), and implementing a co-location configuration where a DCFC station is connected to an existing meter within a commercial building. Results show that while the median electricity cost across more than 7000 commercial retail rates remains less than $0.20/kWh for all charging load scenarios considered, cost varies greatly, and some locations do experience significantly higher electricity cost. Co-location is almost always economically viable to mitigate fixed cost and demand charges, but the relative benefit of co-locating diminishes as station size and utilization increase. Energy storage alone can help mitigate demand charges and is more effective at reducing costs for “peaky” or low-utilization loads. On the other hand, PV systems primarily help mitigate energy charges, and are more effective for loads that are more correlated with solar production, even in areas with lower solar resource. PV and energy storage can deploy synergistically to provide cost reductions for DCFC, leveraging their ability to mitigate demand and energy charges.

Modeling and Analysis of a Fast Charging Station and Evaluation of Service Quality for Electric Vehicles

The deployment of public charging infrastructure networks has been a major factor in enabling electric vehicle (EV) technology transition and must continue to support the adoption of this technology. DC fast charging (DCFC) increases customer convenience by lowering charging time, enables long-distance EV travel, and could allow the electrification of high-mileage fleets. Yet, high capital costs and uneven power demand have been major challenges to the widespread deployment of DCFC stations. There is a need to better understand DCFC stations’ loading and customer service quality. Furthermore, the relationship between the initial investment decision on building certain number of ports and customer satisfaction should be quantified. This paper aims to analyze these aspects using one million vehicle days of travel data within the Columbus, OH, USA, region. Monte Carlo analysis is carried out in three types of areas—urban, suburban, and rural—to quantify the effect of uncertain parameters on DCFC station loading and service quality. Additional simulations based on a homogeneous vehicle population are carried out, and closed-form equations are derived therefrom to estimate charging duration and waiting time in the queue. Optimization of DCFC station design is also addressed through the number and capacity of ports.

System Design and Optimization of In-Route Wireless Charging Infrastructure for Shared Automated Electric Vehicles

Deploying shared automated electric vehicles (SAEVs) on current roadways in cities will significantly shape current transportation systems and make our urban mobility systems more efficient, convenient, and environmentally friendly. Utilizing wireless power transfer (WPT) technology to charge the SAEVs provides perfect fits for realizing a fully automated mobility system. However, the investment in wireless charging infrastructure (WCI) presents a critical barrier for commercializing and adopting this technology. The barrier can be cleared by realizing the proper design of the WPT system that maximizes the benefits and minimizes the cost of WCI at the same time. This paper introduces a system design optimization tool and methodology for WCI for serving fixed-route SAEVs in automated mobility districts (AMDs). The tool offers the capability of integrating driving data (simulated or collected from the real world), vehicle parameters (e.g., battery, motor, dimensions, and so on), and wireless charger characteristics (rate, locations, alignment, and so on) to generate energy and state-of-charge profiles for each vehicle, considering motoring, regenerative braking, and charging. Furthermore, the proposed tool incorporates a multi-objective optimization layer for searching the optimum design parameters based on predefined objectives and constraints. The proposed method was utilized to design the WCI for a hypothetical AMD scenario with four SAEVs. The outcomes show that implementing in-route wireless chargers at designated stops for the SAEVs with maximum power level has the potential to provide a charge sustaining operation with 52% reduction in the on-board battery and presents the most cost-effective solution. The proposed solution is assessed in comparison with other charging technologies, such as stationary WPT and dc fast charging, and it shows the most feasible option for an AMD network in terms of cost, convenience, and performance.

Investigation of the potential to improve DC fast charging station economics by integrating photovoltaic power generation and/or local battery energy storage system

The economic feasibility of DC Fast Charging (DCFC) stations is strongly impacted by electricity charges, billed by electricity consumption (kWh) and power demand (kW), that have to be paid to the local utility. In this simulation study, the possibilities to significantly improve DCFC economics by reducing these utility charges have been investigated for DCFC stations assumed to be installed at highway service centres in Ontario and in Alberta (Canada).Various scenarios, in which the DCFCs are complemented by local photovoltaic (PV) power generation and/or a battery energy storage system (BESS), are evaluated against a reference case with only a grid connection. The discounted payback periods of the required additional capital investments have been examined. The analysis results indicate that the proposed systems are able to reduce the demand charges due to the addition of BESS and reduce the electricity consumption charges due to the utilization of PV. Although the proposed systems cannot pay themselves back within a reasonable period under the current PV and battery prices, the economic viability in a 5- to 10-year timeframe becomes quite promising considering the expected continuous decline of these prices because of technology advancement, manufacturing efficiencies and market expansions.

Smart Charging Strategy for Electric Vehicle Charging Stations

Although the concept of transportation electrification holds enormous prospects in addressing the global environmental pollution problem, in reality the market penetration of plug-in electric vehicles (PEVs) has been very low. Consumer concerns over the limited availability of charging facilities and unacceptably long charging periods are major factors behind this low penetration rate. From the perspective of the electricity grid, a longer PEV peak load period can potentially overlap with the residential peak load period, making energy management more challenging. A suitably designed charging strategy can help to address these concerns, which motivated us to conduct this research. In this paper, we present a smart charging strategy for a PEV network that offers multiple charging options, including ac level 2 charging, dc fast charging, and battery swapping facilities at charging stations. For a PEV requiring charging facilities, we model the issue of finding the optimal charging station as a multiobjective optimization problem, where the goal is to find a station that ensures the minimum charging time, travel time, and charging cost. We extend the model to a metaheuristic solution in the form of an ant colony optimization. Simulation results show that the proposed solution significantly reduces waiting time and charging cost.

Research and Construction of DC Energy Measurement Traceability Technology

With the implementation of energy saving and emission reduction policies, DC energy metering has been widely used in many fields. In view of the lack of a DC energy measurementtraceability system, in combination with the process of downward measurement transfer in relation to the DC charger-based field calibration technology and DC energy meter and shunt calibration technologies, the paper proposed DC fast charging, high DC, small DC voltage output and measuring technologies, and built a time-based plan by converting high DC voltage into low voltage and high current into low current and then into low voltage, leaving DC energy traceable to national standards in terms of voltage, current and time and thus filling in the gap in DC energy measurement traceability.