Plug-in vehicles can behave either as loads or as a distributed energy and power resource in a concept known as vehicle-to-grid (V2G) connection. This paper reviews the current status and implementation impact of V2G/grid-to-vehicle (G2V) technologies on distributed systems, requirements, benefits, challenges, and strategies for V2G interfaces of both individual vehicles and fleets. The V2G concept can improve the performance of the electricity grid in areas such as efficiency, stability, and reliability. A V2G-capable vehicle offers reactive power support, active power regulation, tracking of variable renewable energy sources, load balancing, and current harmonic filtering. These technologies can enable ancillary services, such as voltage and frequency control and spinning reserve. Costs of V2G include battery degradation, the need for intensive communication between the vehicles and the grid, effects on grid distribution equipment, infrastructure changes, and social, political, cultural, and technical obstacles. Although V2G operation can reduce the lifetime of vehicle batteries, it is projected to become economical for vehicle owners and grid operators. Components and unidirectional/bidirectional power flow technologies of V2G systems, individual and aggregated structures, and charging/recharging frequency and strategies (uncoordinated/coordinated smart) are addressed. Three elements are required for successful V2G operation: power connection to the grid, control and communication between vehicles and the grid operator, and on-board/off-board intelligent metering. Success of the V2G concept depends on standardization of requirements and infrastructure decisions, battery technology, and efficient and smart scheduling of limited fast-charge infrastructure. A charging/discharging infrastructure must be deployed. Economic benefits of V2G technologies depend on vehicle aggregation and charging/recharging frequency and strategies. The benefits will receive increased attention from grid operators and vehicle owners in the future.

Review of the Impact of Vehicle-to-Grid Technologies on Distribution Systems and Utility Interfaces

Plug-in hybrid electric vehicles are a midterm solution to reduce the transportation sector's dependency on oil. However, if implemented in a large scale without control, peak load increases significantly and the grid may be overloaded. Two algorithms to address this problem are proposed and analyzed. Both are based on a forecast of future electricity prices and use dynamic programming to find the economically optimal solution for the vehicle owner. The first optimizes the charging time and energy flows. It reduces daily electricity cost substantially without increasing battery degradation. The latter also takes into account vehicle to grid support as a means of generating additional profits by participating in ancillary service markets. Constraints caused by vehicle utilization as well as technical limitations are taken into account. An analysis, based on data of the California independent system operator, indicates that smart charge timing reduces daily electricity costs for driving from $0.43 to $0.2. Provision of regulating power substantially improves plug-in hybrid electric vehicle economics and the daily profits amount to $1.71, including the cost of driving.

Optimal Charge Control of Plug-In Hybrid Electric Vehicles in Deregulated Electricity Markets

The virtual synchronous generator (VSG) is a control scheme applied to the inverter of a distributed generating unit to support power system stability by imitating the behavior of a synchronous machine. The VSG design of our research incorporates the swing equation of a synchronous machine to express a virtual inertia property. Unlike a real synchronous machine, the parameters of the swing equation of the VSG can be controlled in real time to enhance the fast response of the virtual machine in tracking the steady-state frequency. Based on this concept, the VSG with alternating moment of inertia is elaborated in this paper. The damping effect of the alternating inertia scheme is investigated by transient energy analysis. In addition, the performance of the proposed inertia control in stability of nearby machines in power system is addressed. The idea is supported by simulation and experimental results, which indicates remarkable performance in the fast damping of oscillations.

Power System Stabilization Using Virtual Synchronous Generator With Alternating Moment of Inertia

Virtual synchronous generators: A survey and new perspectives

Plug-in hybrid electric vehicles (PHEVs) are the next big thing in the electric transportation market. While much work has been done to detail what economic costs and benefits PHEVs will have on consumers and producers alike, it seems that it is also important to understand what impact PHEVs will have on distribution networks nationwide. This paper finds that the impact of PHEVs on the distribution network can be determined using the following aspects of PHEVs: driving patterns, charging characteristics, charge timing, and vehicle penetration. The impacts that these aspects of PHEVs will have on distribution networks have been measured and calculated by multiple authors in different locations using many different tools that range from analytical techniques to simulations and beyond. While much work has already been completed in this area, there is still much to do. Areas left for improvement and future work will include adding more stochasticity into models as well as computing and analyzing reliability indices with respect to distribution networks.

The impact of plug-in hybrid electric vehicles on distribution networks: A review and outlook

This paper determines a simulation model to create realistic driving patterns for a fleet of vehicles (availability analysis) and a model to calculate the energy consumption (Wh/km) of electric vehicles (EVs). The first model creates a unique driving behavior for each vehicle in the fleet, based on Flemish data on travel behavior. The second model calculates the energy consumption of EVs based on representative driving cycles and vehicle characteristics based on data sheets from manufacturers. The main contribution of this paper is to show the decoupling of both models. The results of the energy consumption calculations can be used as an input for the availability analysis to calculate the energy demand and to determine the battery state of charge (SoC). As such, it is not necessary to have the drive cycles as an input for the availability analysis, which would drastically slow down these simulations because of a different time scale (second versus minute scale). Both models will be used to analyze the battery sizing for battery electric vehicles (BEVs). Since the specific energy consumption depends on several vehicle parameters. The sensitivity to these parameters on the energy requirements (from the availability analysis) will be discussed. Also the power requirements (from the energy consumption calculations) will be checked.

An Availability Analysis and Energy Consumption Model for a Flemish Fleet of Electric Vehicles

This paper presents the power electronic platform used for the VSYNC project. In this project, inverters are controlled in such a way as to exhibit a virtual rotational inertia towards the grid, in order to limit grid frequency variations in grids containing a high share of inverter-connected DER. First the layout and operation of the platform are described in detail, showing its versatility for research purposes. Next the performance of the platform is illustrated using experimental results obtaining using a grid-connected inverter in a laboratory setup.

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Layout and performance of the power electronic converter platform for the VSYNC project

The paper examines the interaction between grid-coupled full hybrid electric vehicles (HEV) and the grid. The interaction allows the hybrid vehicle to travel a significant part of the time in all-electric mode. On the other hand, the grid coupling allows the grid to use the hybrid car as a controllable load and energy storage facility, enabling a higher penetration of variable generation units, such as renewable sources based on wind and photovoltaic cells. Experiments with a battery, grid connection and induction machine prove the feasibility of these grid-coupled hybrid electric vehicles. 1 Introduction The batteries currently used in HEVs are expensive and heavy, leading to a low specific energy content. Through the rapid development of batteries the cost per kWh diminishes while the specific energy content rises. As a consequence, larger amounts of energy can be stored in an economic way for the electric propulsion of HEVs and larger distances can be travelled in an all-electric “emission free” mode. An estimated 85 % of fuel (not energy) savings can be achieved if the vehicle has an all-electric driving range of 100 km [6]. In order to achieve this kind of fuel savings, the battery needs to be charged with electrical energy from the grid, as opposed to the current practice where a combustion engine powers an on-board electric generator to produce electric energy. The only requirement to make this happen is a grid coupling. This grid coupling makes a variety of interactions possible between a fleet of HEVs and the grid [1,5]. From the perspective of the hybrid fleet, the grid coupling enables a lower energy cost and a reduction in environmental pollution, on condition that the electric energy production itself is environmently friendly. From the perspective of the grid the fleet of hybrid electric vehicles can act as a controllable load to smooth grid load. Power electronics for the grid coupling, can provide reactive power to enhance the power factor of the installation and can be used as an active filter to eliminate harmonics. By injecting electrical energy in the grid, the HEV can be used as reserve power unit to set off the loss of a power plant, as replacement for peak power units, as part of a microgrid or as stand-alone mobile generator. Other possibilities such as peak-shaving are possible from a technical point of view, but lack the necessary economical feasibility.

Grid power quality improvements using grid-coupled hybrid electric vehicles

Internal combustion engines (ICE) are combined with electric motors and batteries in both hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV) to improve efficiency and achieve a limited all electric range. This paper determines the electrical power required for charging a fleet of PHEVs in Belgium. A stochastic model based on the driving behavior of Western European drivers, determines the availability of the PHEVs for grid charging.

Impact-analysis of the charging of plug-in hybrid vehicles on the production park in Belgium

The aim of this paper is to investigate the impact of the current ripple, originating from the dc-dc converter of e.g. a PHEV powertrain, on the ageing of Li-ion batteries. Most research concerning batteries focuses on very low (μHz) to low (Hz) frequencies and low current ripples to create very accurate battery models which can determine e.g. the State of Charge of the battery. On the other hand the design of dc-dc converters tries to reduce the current ripple by using multiple phases with interleaving technique and capacitors in parallel with the battery. The interaction between the current ripple of the dc-dc converter and the battery has received little attention so far. A test set-up is build with two identical 304 V , 12 kWh Li-ion batteries and two 100 A dc-dc converters. The dc-dc converter can be connected to an LCL-filter or solely to the primary inductor of this filter, such that the battery current contains a small or large current ripple respectively. The batteries are discharged and charged to simulate the circumstances in which a plug-in hybrid electric vehicle is used. After each month, during which the battery either experiences a small or large current ripple, characterization tests are performed to establisch the ageing of the batteries. Based on the test results, the current ripple does not appear to have a measurable impact on the battery resistance and the Discharge and Regen Power. There is an increase of the resistance and a decrease of the Discharge and Regen Power, but this is to be expected as the battery packs are submitted to 3 months of Combined Cycle Life Testing. The temperature of the battery turns out to be far more important for the resistance and attained power levels of the batteries. The absent effect of the current ripple on the ageing of the batteries may be due to the intrinsic double-layer capacitor. This capacitor at the surface of the electrodes carries part of the current ripple and reduces the current ripple as experienced by the actual charge transfer reaction which carries the dc-part of the current.

https://www.mdpi.com/2032-6653/6/3/532/pdf

Sven De Breucker

Papers

An Availability Analysis and Energy Consumption Model for a Flemish Fleet of Electric Vehicles

Layout and performance of the power electronic converter platform for the VSYNC project

Grid power quality improvements using grid-coupled hybrid electric vehicles

Impact-analysis of the charging of plug-in hybrid vehicles on the production park in Belgium

Impact of current ripple on Li-ion battery ageing