Bidirectional Charger Research Articles

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.

A New Control Strategy for Energy Management of Bidirectional Chargers for Electric Vehicles to Minimize Peak Load in Low-Voltage Grids with PV Generation

This paper introduces a new bidirectional vehicle-to-grid (V2G) control strategy for energy management of V2G charging points equipped with photovoltaic systems (PVs), considering the interaction between V2G chargers, electric vehicle (EV) owners, and the network operator. The proposed method aims to minimize peak load, grid infeed power, feeder loading, and transformer loading by scheduling EVs charging and discharging. The simulation experiments take into account three EV battery capacities as well as two levels of EV penetration. In order to validate the effectiveness of the proposed approach, five scenarios are studied in a single feeder of a low-voltage (LV) distribution network in DIgSILENT PowerFactory, which comprises a combination of residential and commercial loads as well as PV systems. Simulation results demonstrate that the proposed V2G strategy improves the paper’s objectives by providing ancillary services to the grid.

Balancing the Grid with V2G

Bidirectional battery charging could be the key to unlocking the potential of V2G technology

Energy management for solar-hydrogen microgrids with vehicle-to-grid and power-to-gas transactions

This study addresses the energy management of an integrated solar-hydrogen microgrid. The microgrid includes zero-emission vehicles, renewable energy sources, an electrolyzer, bidirectional charging stations, and a hydrogen refueling station with hydrogen storage. Vehicle-to-grid (V2G) charging stations can alleviate renewable electricity variability by discharging the energy of vehicle batteries back to the grid. The electrolyzer can absorb excess solar generation to balance supply and demand with power-to-gas (P2G) transactions. Given the uncertainties from intermittent renewable generation and energy demand, a two-stage stochastic optimization framework derives the optimal power management strategy for the component subsystems, aiming to minimize operating costs. The first stage of the model determines the day-ahead charging price and power supply for electric vehicle charging and hydrogen production, and the second stage performs real-time energy scheduling under different scenarios. The performance of the proposed optimization strategy is examined through a case study using real-world data, and the results demonstrate that daily operating costs can be reduced by up to 27.5%. Moreover, inclusion of the P2G process with hydrogen storage yields better performance to support peak shaving and reducing costs compared to using V2G or dynamic pricing-based demand response policies only.

Profitability of V2X under uncertainty: Relevant influencing factors and implications for future business models

Intelligent, bidirectional charging strategies (vehicle-to-X, V2X) are a crucial part of the decarbonization of the transport sector. To facilitate the successful rollout of business models associated with V2X, we identify revenue potentials for different use cases, additional costs, and resulting profits for future years. Our assessments result in ranges of profits for different V2X types with the spread of profits providing a measure of uncertainty. The profit analysis shows that some V2X types can most certainly become profitable in the near future. For vehicle-to-home (V2H), for instance, profits of 390 € per vehicle and year in 2040 are determined, if viewed optimistically. Other V2X types (vehicle-to-business, V2B, and vehicle-to-grid, V2G) are subject to high uncertainties, where high as well as low or no profits are possible for future years. External circumstances are found to be of great impact regarding V2X profitability with user type and location being most relevant. Based on this, we derive business model implications and draw conclusions for a well-considered business model design. To mitigate uncertainties and increase the change of profitability, the focus of business model development should be on customer segments, revenue streams and value propositions.

Rethinking of Bidirectional Charging

Rethinking of Bidirectional Charging

Electric Vehicle-to-Grid (V2G) Technologies: Impact on the Power Grid and Battery

The gradual shift towards cleaner and green energy sources requires the application of electric vehicles (EVs) as the mainstream transportation platform. The application of vehicle-to-grid (V2G) shows promise in optimizing the power demand, shaping the load variation, and increasing the sustainability of smart grids. However, no comprehensive paper has been compiled regarding the of operation of V2G and types, current ratings and types of EV in sells market, policies relevant to V2G and business model, and the implementation difficulties and current procedures used to cope with problems. This work better represents the current challenges and prospects in V2G implementation worldwide and highlights the research gap across the V2G domain. The research starts with the opportunities of V2G and required policies and business models adopted in recent years, followed by an overview of the V2G technology; then, the challenges associated with V2G on the power grid and vehicle batteries; and finally, their possible solutions. This investigation highlighted a few significant challenges, which involve a lack of a concrete V2G business model, lack of stakeholders and government incentives, the excessive burden on EV batteries during V2G, the deficiency of proper bidirectional battery charger units and standards and test beds, the injection of harmonics voltage and current to the power grid, and the possibility of uneconomical and unscheduled V2G practices. Recent research and international agency reports are revised to provide possible solutions to these bottlenecks and, in places, the requirements for additional research. The promise of V2G could be colossal, but the scheme first requires tremendous collaboration, funding, and technology maturation.

An overview of bidirectional electric vehicles charging system as a Vehicle to Anything (V2X) under Cyber–Physical Power System (CPPS)

Nowadays, EVs are rapidly increasing in popularity, and are accepted as the vehicles of the future all over the world. The most important components are their battery and charging systems. The energy capacity of EVs’ batteries has a significant potential to supply different energy requirements. Therefore, EVs must be designed in accordance with bidirectional power flow, and Electric Vehicle Supply Equipment (EVSE) should be upgraded as Electric Vehicle Power Exchange Equipment (EVPE). This power exchange infrastructure can be called Vehicle-to-Anything (V2X). V2X will also be the key solution for energy grids of the future that will turn into a much larger and smarter system with the help of emerging digitalization technologies, such as Artificial Intelligence (AI), Distributed Ledger Technology (DLT), and the Internet of Things (IoT). This study introduces a multi-layer Cyber–Physical Power Systems (CPPS) framework to explore the potential of V2X technologies allowing bidirectional charging. In addition, the impact of e-mobility is discussed from the V2X perspective. V2X has the potential to provide more practical use of electric vehicles and to bring advantages to the user in terms of both economy and comfort, thus accelerating the transformation of e-mobility and making it easier to accept.

Main Circuit Topology and Electromagnetic Interference of Electric Vehicle Bidirectional Charger

In order to improve the electromagnetic compatibility performance of electric vehicle bidirectional chargers, the authors propose a main circuit topology and electromagnetic interference of the electric vehicle bidirectional charger. The design adopts the parallel connection of silicon carbide (SiC) MOSFETs and completes the bidirectional charging system based on the cascade connection of dual active bridge (DAB) and three-phase four-wire inverter. This paper mainly analyzes the influence of parasitic inductance on the drive and power loop of the T0-247 packaged switch in actual use, and according to the operating characteristics of the system, different gate resistors are used to reduce switching losses and improve system efficiency. And, we explore on how to reduce the overshoot voltage through the RC absorption circuit, thereby reducing the conducted interference. The result shows the following: the primary side absorption circuit resistance is 470 Ω and the capacitor is 47 nf, the secondary side absorption circuit resistance is 40 Ω and the capacitance is 4.7 nf, and the circuit power is 5000 W. Under the same conditions, without adding the RC absorption circuit, the conducted interference on the AC side does not meet the standard, and the amount of disturbance is large. After adding a suitable RC absorption circuit, the conducted interference on the AC side reaches the required value. Conclusion. This research provides a systematic design scheme and optimization method for designing power electronic devices using SiC.

Design Methodology of Bidirectional Resonant CLLC Charger for Wide Voltage Range Based on Parameter Equivalent and Time Domain Model

The bidirectional CLLC resonant converter has distinguished potential in battery chargers and energy storage systems for its advantages in soft switching and bidirectional power flow capability. However, traditional CLLC converters generally adopt symmetrical design to maintain bidirectional symmetrical characteristics, which means the secondary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network is designed to be equal to the primary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network after reflection. The symmetrical design is only suitable for voltage grade matching scenarios where a wide voltage range is not required, such as CLLC-type dc transformers. Whereas in the field of bidirectional chargers, due to the wide voltage range of battery, there are significant differences in the characteristics required between charging and discharging mode, which makes symmetrical design no longer applicable. To cope with this issue, this paper proposes a novel design methodology of CLLC based on parameter equivalent and time domain model. With the parameter equivalent principle, the CLLC resonant tank with arbitrary parameters is investigated to satisfy the requirements of wide voltage range for bidirectional charger application. Compared with the symmetrical design, the proposed method can meet the requirements of bidirectional gain within preset frequency range and guarantee the achievement of zero-voltage switching under required load conditions with the minimum reactive power. In addition, the area product capacity of the magnetic part of the CLLC resonant tank is minimized based on the parameter equivalent principle. Finally, experiments have been performed on a 1 kW prototype to confirm the validity and feasibility of the proposed design methodology.

Synergy of Unidirectional and Bidirectional Smart Charging of Electric Vehicles for Frequency Containment Reserve Power Provision

Besides the integration of renewable energies, electric vehicles pose an additional challenge to modern power grids. However, electric vehicles can also be a flexibility source and contribute to the power system stability. Today, the power system still heavily relies on conventional technologies to stay stable. In order to operate a future power system based on renewable energies only, we need to understand the flexibility potential of assets such as electric vehicles and become able to use their flexibility. In this paper, we analyzed how vast amounts of coordinated charging processes can be used to provide frequency containment reserve power, one of the most important ancillary services for system stability. Therefore, we used an extensive simulation model of a virtual power plant of millions of electric vehicles. The model considers not only technical components but also the stochastic behavior of electric vehicle drivers based on real data. Our results show that, in 2030, electric vehicles have the potential to serve the whole frequency containment reserve power market in Germany. We differentiate between using unidirectional and bidirectional chargers. Bidirectional chargers have a larger potential but also result in unwanted battery degradation. Unidirectional chargers are more constrained in terms of flexibility, but do not lead to additional battery degradation. We conclude that using a mix of both can combine the advantages of both worlds. Thereby, average private cars can provide the service without any notable additional battery degradation and achieve yearly earnings between EUR 200 and EUR 500, depending on the volatile market prices. Commercial vehicles have an even higher potential, as the results increase with vehicle utilization and consumption.

Value of optimal trip and charging scheduling of commercial electric vehicle fleets with Vehicle-to-Grid in future low inertia systems

The electrification of transport is seen as an important step in the global decarbonisation agenda. With such a large expected load on the power system from electric vehicles (EVs), it is important to coordinate charging in order to balance the supply and demand for electricity. Bidirectional charging, enabled through Vehicle-to-Grid (V2G) technology, will unlock significant storage capacity from stationary EVs that are plugged in. To take this concept a step further, this paper quantifies the potential revenues to be gained by a commercial EV fleet operator from simultaneously scheduling its trips on a day-ahead basis, as well as its charging. This allows the fleet to complete its trips (with user defined trip length and distance), while taking advantage of fluctuating energy and ancillary services prices. A mathematical framework for optimal trip scheduling is proposed, formulated as a mixed-integer linear program, and is applied to several relevant scenarios of the present and future British electricity system. It is demonstrated that an optimal journey start time can increase the revenue of commercial fleets by up to 38% in summer and 12% in winter. This means a single EV from the maintenance fleet can make additional annual revenue of up to {\pounds}729. Flexible trip schedules are more valuable in the summer because keeping EVs plugged in during peak solar output will benefit the grid and the fleet operators the most. It was also found that a fleet of 5,000 EVs would result in the equivalent $\textrm{CO}_2$ of removing one Combined Cycle Gas Turbine from the system. This significant increase in revenue and carbon savings show this approach is worth investigating for potential future application.

Hidden Markov Models-Based Anomaly Correlations for the Cyber-Physical Security of EV Charging Stations

Over recent years, we have seen a significant rise in electric mobility to overcome the anthropogenic emissions by conventional gasoline vehicles. However, the prerequisite of smoothening of peaks and imbalances through bidirectional charging is concatenated with the undesired impacts on reliability and security of power system operation when there are probable intrusions in the eXtreme Fast Charging (XFC) station, hence destabilizing the charging networks. So this paper applies STRIDE based threat modeling to analyze and identify multiple potential threats endured by the cyber-physical system (CPS) of XFC station by using weighted attack defense tree. Potential mitigation strategies are then suggested for the identified severe threats. In addition, this paper also develops a stochastic probabilistic tool, the Hidden Markov Model (HMM) for modeling the security attacks for a given range of identified attack vectors and hence employing an appropriate defense strategy against the malicious hacker. Also, a weighted attack defense tree has been developed to generate various attack scenarios. In the end, the results of the proposed work are substantiated and validated if it is able to considerably improve overall charging efficiency and cyber-physical security of the charging station network.

Synchronization Strategy Based on Resonant Current Detection for Bidirectional Wireless Charging System

Bidirectional wireless power transfer (BWPT) greatly improves the reliability of power supply. However, wireless communication between the primary and pickup controllers is usually required to transmit load information, which has time delay and is easily interfered by electromagnetic fields. Existing solutions to avoid the use of communication can be divided into three categories: additional DC/DC circuit, primary side bridge control and secondary side bridge control. Compared with the other two methods, the secondary side bridge control has low loss and good robustness. But it usually requires Phase-Locked Loop (PLL) to eliminate the frequency error between primary and secondary side bridges, which increases the complexity. In this paper, a constant current control strategy without communication is proposed. It is based on the secondary side bridge control and the switching sequence of the secondary side bridge is periodically synchronized according to the phase of the resonant current. It works robustly without the need for additional hardware such as PLL or Multiplier. The harmonic sensitivity analysis, parameter optimization design and stability analysis are carried out to improve the control efficiency. Experimental results based on a 1kW prototype with dual LCC resonant network are presented to verify the effectiveness of the proposed control strategy.

Design of a bi-directional DC/DC converter for EV chargers oriented to V2G applications

In order to address the problems caused by climate change, electric vehicles have gained international attention in recent years. Furthermore, special attention is being paid to the Vehicle to Grid (V2G) services that this technology can provide. In this context, the development of bi-directional chargers is gaining importance. Taking all this into consideration, in this work a simple and easy-to-implement solution of the DC/DC stage of a bidirectional electronic charger that allows the integration of EVs in V2G applications has been designed and validated through simulation.

Robust Tracking Control of a Three-Phase Bidirectional Charger for Electric Vehicle

This paper presents a robust control strategy for an electric vehicle's three-phase off-board bidirectional AC-DC battery charger. The conventional constant current (CC) and constant voltage (CV) charging mode are considered to provide a fast-charging performance for the batteries. The bidirectional charger also allows using of the vehicle as an energy storage system for the grid i.e., charging during the peak-off times and delivering the energy back to the grid during peak times of electrical consumption. In discharging mode, the bidirectional charger maintains constant active power flow to the grid with a given reference. For both cases, user of a robust state feedback controller with integral action is made in the DQ-synchronous frame. The set of stabilizing gains of this controller are determined by a linear matrix inequality (LMI)-based optimization so that the convergence time to steady stead is minimized in the occurrence of the parametric uncertainties of the L-filter. The efficacy of the proposed controller is verified through simulation and experimental results on 102.4 V Lithium iron phosphate (LiFePO4) batteries.

Probabilistic optimal management of active and reactive power in distribution networks using electric vehicles with harmonic compensation capability

Electrical vehicles (EVs) are among the fastest-growing electrical loads that change both temporally and spatially at distribution networks. Moreover, the existence of uncertain parameters, such as EVs as well as domestic loads in power networks, poses serious operational challenges for them. Accordingly, stochastic studies of system performance are a must. Against this background, this paper aims to present a stochastic multi-objective method for the problem of simultaneous active and reactive power management as well as harmonic compensation in distribution networks in the presence of EVs and non-linear devices (NLDs). This method minimizes costs associated with power generation and losses. Besides, it improves the total harmonic distortion of voltage (THDv) at network buses subject to network and EV constraints. In the proposed method, to strike a balance between exploration and exploitation abilities, a hybrid technique named the “PSO-GA optimization algorithm” was used to take advantage of both the genetic algorithm (GA) and the particle swarm optimization (PSO) method. Accordingly, the effectiveness of the proposed method was examined on a standard IEEE 33-bus distribution network populated with EVs equipped with on-board bidirectional chargers. The results obtained showed that the proposed model improved network power quality indices as well as economic and technical issues of EVs in parking lots.

Idealized analysis of relative values of bidirectional versus unidirectional electric vehicle charging in deeply decarbonized electricity systems

SummaryWe employed an idealized macro-energy system model to examine how the value of unidirectionally- and bidirectionally-charging electric vehicles (EVs) varies with EV penetration and mix of electricity generators. We find that EVs can help wind and solar-based electricity generation systems to be less costly by making better use of power that would otherwise be curtailed and, potentially, by giving electricity back to the grid at times of peak net load. At low levels of EV penetration, bidirectional EVs are valuable because they can provide electricity at times of main load peak. At today’s low levels of EV penetration, bidirectional EVs stimulate investments in solar and wind generation and substantially reduce the need for grid-battery storage compared to unidirectional EVs. At high levels of EV penetration, generation capacity must be increased, and most peaks in main net load demand can be met by reductions in charging by unidirectional EVs.

Impact of behind-the-meter optimised bidirectional electric vehicles on the distribution grid load

The bidirectional charging of electric vehicles (EVs) can foster the energy transition. The growing number of EVs permit different options for integrating them into electricity grids. Therefore, an energy system model to simulate of low voltage grids is expanded with an optimisation algorithm. More than 1000 real low voltage grids were combined with future scenarios regarding photovoltaic plants (PV), electric heating and mobility to evaluate the grid load. Due to these new loads, 42% of the grids need to be expanded by 2040. Optimisation at a building level is not compulsorily grid-supportive so that neither PV self-consumption optimisation nor peak shaving at commercial units can significantly decrease the number of affected grids. In both cases, bidirectional charging capability is only slightly beneficial for the grid. Applying variable market prices to the flexibility options without considering the local grid situation leads to very high simultaneous charging powers of 10 kW/EV, even for many EVs. In contrast, simultaneity decreases to 3 kW/EV from 30 EVs without variable prices. The higher simultaneities also lead to higher grid loads, and therefore, the percentage of grids needing expansion measure rises to 71%, primarily due to too high transformer utilisation and violations of the voltage conditions.

Design and Analysis of Bidirectional Battery Charger with Grid-to-Vehicle, Vehicle-to-Grid and Vehicle-to-Home Technologies

In this fast-changing world, Electric Vehicle (EV) is a giant leap in the world of transportation. In comparison with fossil fuel powered vehicles, EVs are more efficient, silent, emit less pollution while in use and they act as mobile power banks, these makes them a better alternative. This in turn can be used for Vehicle to Home (V2H) and Grid to Vehicle (G2V) operations using IOT as a platform to achieve control and monitoring, prototype IOT based car is considered as the EV in this research. In this research, IOT is used as the platform to implement V2H and G2V concepts. This paper presents the development of an on-board bidirectional battery charger for Electric Vehicles (EVs) targeting Grid-to-Vehicle (G2V), Vehicle-to-Grid (V2G), and Vehicle-to-Home (V2H) technologies. During the G2V operation mode the batteries are charged from the power grid with sinusoidal current and unitary power factor. During the V2G operation mode the energy stored in the batteries can be delivered back to the power grid contributing to the power system stability. In the V2H operation mode the energy stored in the batteries can be used to supply home loads during power outages, or to supply loads in places without connection to the power grid. The adopted topology and control algorithms are accessed through computer simulations and validated by experimental results achieved with a developed laboratory prototype operating in the different scenarios. KEYWORDS: bidirectional Battery-charger, Grid-to-Vehicle (G2V); Vehicle-to-Grid (V2G); Vehicle-to-Home (V2H)