DC Fast Charging Research Articles

Real-Time Open-Circuit Fault Diagnosis Method for T-Type Rectifiers Based on Median Current Analysis

T-type rectifiers are widely used in DC fast chargers, super uninterrupted power supplies, renewable energy, and other low-voltage and medium-voltage rectifier applications. High equipment reliability and high-quality power are often required in these applications but are damaged by the transistor open-circuit fault. This paper proposes a novel real-time open-circuit fault diagnosis method for the T-type rectifier based on median current analysis. The method only uses the three-phase currents to obtain the median current and realize the diagnosis. In the rectifier, partial open-circuit faults result in weak fault signals, making the diagnosis challenging. To solve this, the median current obtained by the currents performs fault frequency modulation to enhance the fault signals at first. Then, the ratio of the fundamental frequency to the dc component is used to realize fault detection. The inner/outer fault is identified at the same time. At last, the fault transistor is located by simple change point detection. The change points determine the fault phase and transistor fault. The effectiveness and robustness of the proposed method are verified by the experiment results.

Smart Self Monitoring Eco Friendly EV Charging Station

Due to their low expenses for operation and commitment to the environment, electric cars (EVs) are growing in popularity. However, the inadequate charging infrastructure limits their popularity. To keep their vehicles always ready for use, EV owners need access to convenient and dependable charging stations. Thus, promoting the adoption of EVs requires the installation of electric charging stations. A specialized infrastructure called an electric charging station is created to supply electricity to electric vehicles. It is made up of a unit for charging, one for distributing power, and one for communicating. The charging unit is in charge of feeding electricity from the grid to an electric vehicle's battery. The electric car receives power from the charging unit through the power distribution unit. To make sure that the charging process is secure, dependable, and effective, the communication unit is in charge of maintaining communication between the charging station and the electric car. There are two categories of electric charging stations: DC rapid charging stations and AC charging stations. While DC fast charging stations offer a faster charging rate of up to 350 kW, AC charging stations offer a slower rate of up to 22 kW. Although installing DC fast charging stations costs more money, they are essential for long- distance travel and in places where there is a high demand for quick charging.

Simulation of Electric Vehicle with DC Fast Charging for V2G and G2V Operation

Simulation of Electric Vehicle with DC Fast Charging for V2G and G2V Operation

Modular Multiport Electric-Vehicle DC Fast-Charge Station Assisted by a Dynamically Reconfigurable Stationary Battery

Multi-port Battery-Assisted dc Fast Charger (BA-DCFC) stations enable high charge rates of Electric Vehicles (EVs) at sites that have insufficient grid capacity. However, BA-DCFCs are expensive and inefficient due to the Battery Energy Storage System (BESS) and high-power isolated dc-dc converters that interface the BESS and EV charging ports. This paper presents a modular multi-port dc Linear Fast Charger (LFC) for EVs, which uses a stationary, reconfigurable Battery Energy Storage System (rBESS), a current-mode, digitally controlled bi-directional Linear Regulator (LR), and a contactor matrix. The LFC LR increases the overall station efficiency and eliminates the volume and cooling complexity associated with the high-power magnetics, high-voltage capacitors and high-frequency switches of state-of-the-art (SotA) isolated dc-dc converters. Compared to a SotA isolated dc-dc converter, the LR experiences 83.6% less loss for the same rated EV charge power. Over a day of typical operation, a three-port LFC station is shown to have 28% less loss than a state-of-the-art BA-DCFC, with an average efficiency of 93.4%. The LFC achieves redundancy at the station, BESS and LR levels while also integrating active balancing of state-of-charge/health without auxiliary switched-mode converters. The proposed system is verified using full-scale transient simulations and experimental results from a scaled, hardware-in-loop implementation with a custom LR and series-connected battery modules.

The DC fast charging architecture for implementing Vehicle-To-Grid technology within a micro-grid

Abstract: Electric vehicle (EV) batteries have the potential to serve as energy storage devices in micro-grids, aiding in energy management by storing excess energy from the grid (Grid-To-Vehicle, G2V) and supplying energy back to the grid when needed (Vehicle-To-Grid, V2G). To implement this concept, appropriate infrastructure and control systems must be developed. This paper presents an architecture for integrating a V2G-G2V system in a micro-grid using level-3 fast charging technology forEVs. A micro-grid test system is modeled with a dc fast charging station for connecting EVs, and simulation studies are conducted to demonstrate power transfer through V2G-G2V modes of operation. Test results indicate that EV batteries regulate active power in the micro-grid, with the charging station design ensuring minimal harmonic distortion of grid-injected current. Furthermore, the controller exhibits excellent dynamic performance in terms of maintaining dc bus voltage stability.

Critical Comparison of Li-Ion Aging Models for Second Life Battery Applications

Lithium-ion batteries (LIBs) from electrified vehicles (EVs) that have reached the automotive end of life (EoL) may provide a low-cost, highly available energy storage solution for grid-connected systems, such as peak shaving and ancillary services. There are several issues related to the integration of second life batteries (SLBs) in power systems, such as the variability of the pack design and cell chemistry, in-field assessments of the state of health (SoH), and estimations of the expected lifetimes of SLBs in different power system applications. Model-based approaches are commonly used in the automotive industry for estimating/predicting the capacity and power fade trajectories of LIBs during their life. However, a large variety of models are available with different fidelities, complexities, and computational costs. The accuracy of these estimations is critical for the derivation of business models for SLB applications. This paper presents a qualitative and quantitative assessment of the performance of two well-accepted, state-of-the-art aging models, initially developed for automotive applications and here applied to different SLB applications to predict both the capacity and power fade. These models are evaluated with respect to several performance metrics, such as fidelity of estimation and capability of extrapolation outside the calibration data range. The considered models are classified as semi-empirical physics-based and empirical models, respectively. Three different SLB power profiles, bulk energy for DC fast charge stations and two frequency regulation profiles, are considered, corresponding to different ranges of the SoC, C-rates, and battery temperatures, with the aim of exciting different aging mechanisms. The numerical results provide insight for the selection of aging models for SLB applications based on their performances and limitations.

Statistical Analysis of Electric Vehicle Charging Based on AC Slow Chargers

Regarding DC fast chargers, various studies, such as the charge scheduling, have been conducted. On the other hand, research on AC slow chargers has rarely been conducted due to the predictable and simple usage pattern. Despite the long charging times of AC slow chargers, which use the existing electric outlets with relatively low supplied power, these chargers are suitable for daily home charging of electric vehicles (EVs) during the night. Due to their low installation costs, they are likely to be the dominant type of charging equipment. In this paper, the EV charging process based on AC slow chargers, which supply a maximum power of 3 kW from an AC 220 V outlet, is analyzed by constructing a simple charging model. The charging time and fees are statistically derived and investigated. Furthermore, power load curves for charging EVs with the 3 kW charger are observed. From the statistical analyses, we conclude that daily charging of EVs can be an appropriate scenario in using the AC slow chargers, and the power load can be spread without employing any demand response schemes.

Charging forward: deploying EV infrastructure for Uber and Lyft in California

With recent policies such as the Clean Miles Standard in California and Lyft’s announcement to reach 100% electric vehicles (EVs) by 2030, the electrification of vehicles on ride-hailing platforms is inevitable. The impacts of this transition are not well-studied. This work attempts to examine the infrastructure deployment necessary to meet demand from electric vehicles being driven on Uber and Lyft platforms using empirical trip data from the two services. We develop the Widespread Infrastructure for Ride-hail EV Deployment model to examine a set of case studies for charger installation in San Diego, Los Angeles, and the San Francisco Bay Area. We also conduct a set of sensitivity scenarios to measure the tradeoff between explicit costs of infrastructure versus weighting factors for valuing the time for drivers to travel to a charger (from where they are providing rides) and valuing the rate of charging (to minimize the amount of time that drivers have to wait to charge their vehicle). There are several notable findings from our study: (1) DC fast charging infrastructure is the dominant charger type necessary to meet ride-hailing demand, (2) shifting to overnight charging behavior that places less emphasis on daytime public charging can significantly reduce costs, and (3) the necessary ratio of chargers is approximately 10 times higher for EVs in Uber and Lyft compared to chargers for the general EV owning public.

A Hybrid Power Heronian Function-Based Multicriteria Decision-Making Model for Workplace Charging Scheduling Algorithms

This study proposes a new multicriteria decision-making (MCDM) model to determine the best smart charging scheduling that meets electric vehicle (EV) user considerations at workplaces. An optimal charging station model is incorporated into the decision-making for a quantitative evaluation. The proposed model is based on a hybrid power Heronian functions in which the linear normalization method is improved by applying the inverse sorting algorithm for rational and objective decision-making. This enables EV users to specify and evaluate multicriteria for considering their aspects at workplaces. Five different charging scheduling algorithms with ac dual-port L2 and dc fast charging (DCFC) EV supply equipment (EVSE) are investigated. Based on EV users from the field, the required charging time, EVSE occupancy, the number of EVSE units, and user flexibility are found to have the highest importance degree, while charging cost has the lowest importance degree. The experimental results show that in terms of meeting EV users’ considerations at workplaces, scheduling EVs based on their charging energy needs performs better when compared with scheduling them by their arrival and departure times. While the scheduling alternatives display similar ranking behavior for both EVSE types, the best alternative may differ for the EVSE type. To validate the proposed model, a comparison against three traditional models is performed. It is demonstrated that the proposed model yields the same ranking order as the alternative approaches. Sensitivity analysis validates the best and worst scheduling alternatives.

A Review of DC Fast Chargers with BESS for Electric Vehicles: Topology, Battery, Reliability Oriented Control and Cooling Perspectives

The global promotion of electric vehicles (EVs) through various incentives has led to a significant increase in their sales. However, the prolonged charging duration remains a significant hindrance to the widespread adoption of these vehicles and the broader electrification of transportation. While DC-fast chargers have the potential to significantly reduce charging time, they also result in high power demands on the grid, which can lead to power quality issues and congestion. One solution to this problem is the integration of a battery energy storage system (BESS) to decrease peak power demand on the grid. This paper presents a review of the state-of-the-art use of DC-fast chargers coupled with a BESS. The focus of the paper is on industrial charger architectures and topologies. Additionally, this paper presents various reliability-oriented design methods, prognostic health monitoring techniques, and low-level/system-level control methods. Special emphasis is placed on strategies that can increase the lifetime of these systems. Finally, the paper concludes by discussing various cooling methods for power electronics and stationary/EV batteries.

The costs and challenges of installing corridor DC Fast Chargers in California

A national network of DC Fast Charging infrastructure (DCFC) corridors can facilitate connectivity and long-distance travel using battery electric vehicles (BEVs). Optimal locations of such facilities are where BEV drivers have easy access to charging where drivers will not have to make any deviation from their pre-planned trips. Such optimally located corridor DCFCs are usually in remote, underserved communities and immediately next to a highway where they lack the advantages of shared utility infrastructure in an urban setting. Therefore, we find that other studies and industry knowledge of infrastructure investments do not apply to corridor DCFC locations. This study evaluates the full project costs of installing and commissioning 54 DC Fast Chargers in 36 sites located in major transportation corridors in California and finds significant variation in costs between them. While existing studies show costs ranging from $20,000 - $150,000, we find costs range anywhere between $122,000 and $440,000. This data is critical for new investment in the U.S. to construct a national charging network of DC Fast charging corridors. We find that a significant proportion of the full project costs are taken up by on site “make-ready infrastructure” costs that vary greatly due to site-specific factors and design choices. DCFC installations should be considered civil construction projects with significant electrical infrastructure planning and installation that requires the cooperation of many local stakeholders. We find that costs can be greatly reduced by working with local electrical utilities early in the design and site selection stages when possible. Our study finds that some cost shift towards utility side costs can greatly reduce overall construction costs for sites along highways. We also find that grid-connected DCFC design are substantially cheaper than off-grid solar powered DCFC with onsite storage.

Implementation Strategy for DC Fast Charging Stations for Electric Vehicles

Adoption of electric vehicles (EV) has been on a rising trend in the recent past. Provision of public DC fast charging infrastructure at strategic points is one of the major drivers towards the adoption of electric vehicles. This paper develops an implementation strategy for DC fast charging stations as an element in transmission and distribution infrastructure at strategic points to supply electrical energy for the recharging of electric vehicles. Kenya Power Ltd., a distribution utility player in Kenya, is a key stakeholder in the e-mobility ecosystem an is keen on opportunities that can take up extra capacity especially off-peak hence smoothening the load curve, maximizing on the use of transmission and distribution infrastructure as well as exposure to new technology. DC fast charging stations encourage the purchase of electrical vehicles and is one-step closer to a low – carbon economy, using clean transport. A SWOT analysis was used to construct an implementation strategy for EVs charging stations. Financial viability of the project was analysed using payback period, cost-to-benefit ratio, net present value (NPV), and internal rate of return (IRR). The financial indicators suggested that the investment is profitable, hence it is worth to consider it for investment.

On-Board Chargers for High-Voltage Electric Vehicle Powertrains: Future Trends and Challenges

The powertrain voltages in battery electric vehicles (BEVs) have witnessed an upward trend due to advantages such as reduced runtime losses and extremely high DC fast charging power levels; aiding in reduced range anxiety and lower battery charging duration. This trend requires original equipment manufacturers (OEMs) to re-assess the design of electronic sub-assemblies (ESAs). Due to newly released DC fast charging standards, there are implications on the on-board charger (OBC), which is one of the ESAs in a BEV. This paper performs a comprehensive review of identifying system-level and use-case related challenges in transitioning on-board chargers to higher voltages compared to state-of-the-art, while considering the impact of newly introduced DC fast charging standards like Megawatt Charging Systems (MCS) and ChaoJi/ CHAdeMO 3.0. The existing research in academia and proof-of-concept designs compatible for high-voltage on-board charging sub-systems, such as the power factor correction (PFC) and isolated DC-DC conversion stages is consolidated. Due to the demand for integration driven by cost-optimization targets, single-stage, traction-integrated, and auxiliary power unit (APU) integrated on-board chargers are discussed. Finally, the disparity between state-of-the-art technology and future requirements is defined to establish challenges and the direction of future research areas.

DC Charger Circuit Optimization Design and Fast Charging and Discharging Mechanism Research

DC Charger Circuit Optimization Design and Fast Charging and Discharging Mechanism Research

Design and Implementation of DC Fast Charging for 48V LiFePO4 Battery Pack

This research focuses on developing a fast charging system to charge lithium-ion battery packs with a voltage rating of 48 volts. Standard battery charging uses a 0.25 C charging rate, which takes about 4 hours. The charging method in this study uses the constant current, constant voltage (CC-CV) method by adjusting the charging current at a charging rate of 1C, 2C, and 3C from the battery capacity. The buck converter determined the charging current value, setting it to produce a voltage of 53 V and a charging current of 10 A for a 1C charging rate, 20 A for a 2C charging rate, and 30 A for a 3C charging rate. Based on the testing, the battery charging time to reach 80% takes 57 minutes for charging rate 1C, 30 minutes for charging rate 2C, and 26 minutes for charging rate 3C.

Partial-Power Converter Topology of Type II for Efficient Electric Vehicle Fast Charging

The increasing power levels handled by electric vehicle (EV) dc fast chargers will impose additional challenges to the switching devices in order to cope with the efficiency requirements. A cost-effective alternative to achieve highly efficient power conversion is through the partial-power conversion concept. This article validates the advantages of a step-down Type II partial-power converter (PPC), based on the phase-shifted full-bridge converter, for EV fast chargers. By exploiting the reduced voltage range of an EV battery pack along with the reduced power ratio for a Type II PPC, an extremely efficient charging process can be achieved. The concept is validated with the development of a 7-kW demonstrator, and hence, realistic efficiency measurements are obtained. Results indicate the effectiveness of charging a battery by merely handling 13.32% of the power provided to it, with a peak efficiency of 99.11%.

Mitigating the impact of fast charging on distribution grids using vehicle‐to‐vehicle power transfer: A Paris city case study

AbstractThe deployment of DC fast charging stations (DCFCSs) in cities requires costly reinforcement of low‐voltage (LV) distribution grids, due to the high power required. It results in high investments for the station operator as well as for the distribution system operator and limits the profitability of such projects. In this study, a novel concept of fast charging station which reduces the connection to the grid is presented. This station uses Vehicle‐to‐vehicle (V2V) power transfer from a fleet of carsharing electric vehicles to provide a high charging power while mitigating the power demand on the grid. Based on data from a carsharing operator in the city of Paris, a simulation model of a combined carsharing/V2V fast charging system is proposed, allowing to simulate carsharing trips and V2V transfers. The reduction of the grid connections required to provide fast charging is evaluated and the impact of the repeated discharges on the level of service of the carsharing system is discussed. Moreover, simulation of LV distribution grids allows to compare the grid losses of the V2V system with conventional DCFCSs.

Using an Intelligent Control Method for Electric Vehicle Charging in Microgrids

Recently, electric vehicles (EVs) that use energy storage have attracted much attention due to their many advantages, such as environmental compatibility and lower operating costs compared to conventional vehicles (which use fossil fuels). In a microgrid, an EV that works through the energy stored in its battery can be used as a load or energy source; therefore, the optimal utilization of EV clusters in power systems has been intensively studied. This paper aims to present an application of an intelligent control method to a bidirectional DC fast charging station with a new control structure to solve the problems of voltage drops and rises. In this switching strategy, the power converter is modeled as a DC fast charging station, which controls the fast charging of vehicles with a new constant current or reduced constant current method and considers the microgrid voltage stability. The proposed method is not complicated because simple direct voltage control realizes the reactive power compensation, which can provide sufficient injected reactive power to the network. As a result, the test is presented on a fast charging system of electrical outlets with a proposed two-way reactive power compensation control strategy, in which AC/DC converters are used to exchange two-way reactive power to maintain the DC link voltage as well as the network bus voltage in the range of the basis. This charging strategy is carried out through the simulation of fast charge control, DC link voltage control, and reactive power compensation control to adjust the voltage and modify the power factor in the MATLAB software environment and is then verified. Finally, the results indicate that the proposed method can charge with high safety without increasing the battery’s maximum voltage. It can also significantly reduce the charging time compared to the common CV mode.

Direct Electric Vehicle to Vehicle (V2V) Power Transfer Using On-Board Drivetrain and Motor Windings

Vehicle to vehicle (V2V) energy sharing is emerging as an alternate solution to range anxiety and limited charging infrastructure challenges associated with electric vehicles (EVs). The existing off-board dc fast charging options for V2V application found in the literature are not effective due to the additional weight, size and cost of the external charger or interface. In this article, a new V2V interface is proposed in which both EV’s motor winding neutrals and negative rails of on-board drivetrains are directly connected to each other. This further helps in forming an integrated dual bidirectional dc–dc converter to control the direction of power flow. The proposed approach does not require reconfiguration of motor winding or mechanical clutch to arrest the motor from rotating and/or the reconfiguration of drivetrain inverter connections. The major hardware requirement for the proposed approach is, access to the already existing neutral connection of the EV motor phase windings. To achieve dc fast charging, all three-legs of voltage source inverter of energy Provider-EV are switched using interleaved pulsewidth modulation. Furthermore, finite element analysis is presented for 150 kW EV motor model and its performance validation with the high frequency dc current flowing in the motor windings during the V2V operation. A scaled lab prototype is developed to demonstrate the energy sharing between two Lithium-ion battery banks through the proposed direct V2V power transfer concept.

Impact Assessment of Diverse EV Charging Infrastructures on Overall Service Reliability

A higher penetration of EVs may pose several challenges to the power systems, including reliability issues. To analyze the impact of EVs on the reliability of power systems, a detailed EV charging infrastructure is considered in this study. All possible charging locations (home, workplace, public locations, and commercial fast chargers) and different charging levels (level 1, level 2, and DC fast charging) are considered, and seven charging infrastructures are determined first. Then, the reliability impact of each charging infrastructure is determined using the two widely used reliability indices, i.e., the loss of load expectation (LOLE) and the loss of energy expectation (LOEE). The impact of mixed charging infrastructure portfolios is also analyzed by considering two different cases, which included the equal share of all charging infrastructure and charging infrastructure share based on consumer preferences. The performance is analyzed on a well-known reliability test system (Roy Billinton Test System) and different penetration levels of EVs are considered in each case. Test results have shown that fast-charging stations have the worst reliability impact. In addition, it was also observed that mixed charging portfolios have lower reliability impacts despite having a fair share of fast-charging stations.