Real-time control of an electric vehicle charging station while tracking an aggregated power-setpoint

An electric vehicle (EV) charging method which considers the EVs heterogeneity, taking into account the absence of any information about future arrivals and departures, and of the amount of time any charging will take. The method further considers both switch on and off possibilities and not an arbitrarily small minimum charging power. In order to achieve all these objectives, the invention defines novel metrics and uses them to construct a dedicated optimization problem. As the charging power is discontinuous, the minimum charging power not being arbitrarily small, the optimization problem is mixed integer by nature. Further, because the mixed-integer optimization is difficult to perform in real-time, the invention proposes a heuristic for reducing the number of integer variables, thus reducing the complexity of the problem.

Real-Time Control of an Electric Vehicle Charging Station While Tracking an Aggregated Power Setpoint

Jagdish Prasad Achara, Jean-Yves Le Boudec, Mario Paolone, Lorenzo Enrique Reyes Chamorro, Roman Rudnik, Cong Wang

We consider the problem of controlling the charging of electric vehicles (EVs) connected to a single charging station that follows an aggregated power setpoint from a main controller of the local distribution grid. To cope with volatile resources such as load or distributed generation, this controller manages in real time the flexibility of the energy resources in the distribution grid and uses the charging station to adapt its power consumption. The aggregated power setpoint might exhibit rapid variations due to other volatile resources of the local distribution grid. However, large power jumps and minicycles could increase the EV battery wear. Hence, our first challenge is to properly allocate the powers to EVs so that such fluctuations are not directly absorbed by EV batteries. We assume that EVs are used as flexible loads and that they do not supply the grid. As the EVs have a minimum charging power that cannot be arbitrarily small, and as the rapid fluctuations of the aggregated power setpoint could lead to frequent disconnections and reconnections, the second challenge is to avoid these disconnections and reconnections. The third challenge is to fairly allocate the power in the absence of the information about future EVs arrivals and departures, as this information might be unavailable in practice. To address these challenges, we formulate an online optimization problem and repeatedly solve it by using a mixed-integer-quadratic program. To do so in real time, we develop a heuristic that reduces the number of integer variables. We validate our method by simulations with real-world data.

2020

Experimental Validation of the Real-Time Control of an Electric-Vehicle Charging Station

Sherif Alaa Salaheldin Fahmy, Jean-Yves Le Boudec, Mario Paolone, Roman Rudnik

The high penetration of electric vehicles (EVs) charging stations (CSs), together with the progressive availability of distributed energy resources, increases the risk of grid overloading and power-quality degradation. Real-time control has been advocated by the recent literature as an alternative to costly grid reinforcement. Performance of most of the existing control methods is assessed via simulations, and real-field validation is rarely performed. We present the experimental validation of a recently proposed real-time control method for EVs CS. This method works at sub-second scale and allows the CS to adapt to the rapidly changing state of the grid caused by highly volatile energy resources, such as photo-voltaic (PV) plants. The method fairly allocates the available power, proportional to the EVs needs, while minimizing the EVs battery wear due to frequent charging power variations. It tracks an aggregated power-setpoint that comes from the main grid controller by solving a mixed-integer optimization problem. Our main goal is to show that the method works in the field, i.e., it can control the charge of commercial EVs that are connected to a real grid through a CS. The field validation has two challenges. The first one is to study the real-time capabilities of the method and by analysing how fast it computes the control power-setpoints. The second one refers to the handling of the non-ideal response of EVs to the control power-setpoints due to implementation and reaction delays and inaccuracies. The experimental results demonstrate the performance of the method and show that it can be deployed in the field.

IEEE2021

Toward Ultrafast Charging of Electric Vehicles

Massimiliano Capezzali, Stefano Grioni, Hardi Hõimoja, Hans Björn Püttgen, Alfred Rufer, Michail Vasiladiotis

The paper is devoted to the problems arising from the ultrafast (≤ 10 min) charging of an electric vehicle (EV). An ultrafast charging station (UFCS) must provide high power output with minimal influence on the electricity transmission system, which can only be achieved by the application of energy storage acting as an additional buffer between the vehicle and the grid. Besides storage, interfaces between a fast charging station and the outside environment (vehicle, utility grid) must be designed to fulfil a set of requirements. The main challenge is to be found within the specification of parameters for the design of future energy supply systems, providing for fast charging of the vehicle batteries while avoiding solicitations of the local distribution system which exceed its instantaneous power capabilities. The possible impact of an UFCS on the power distribution system is analysed with the stochastic approach, based on the utilisation of such a station. The general aspects of highly variable load profile clearly include the use of energy storage means that must be specified regarding both the energy storage and the instant power capabilities. Different technologies are analysed in terms of performances and costs. In conclusion, one of the important problems facing electric vehicles is the possibility of short-time charging, both as seen from the EV battery itself as well as from the local supply system. In this context, large load variations as seen from the local power system, at multiple levels, must be carefully assessed with special attention to feasible load changes at the coupling points. By addressing these technical issues as well as the financial constraints, the research aims at providing viable solution for broad ultrafast charging systems integration into the power distribution infrastructure.

2012

Toward Ultrafast Charging of Electric Vehicles

Massimiliano Capezzali, Stefano Grioni, Hardi Hõimoja, Hans Björn Püttgen, Alfred Rufer, Michail Vasiladiotis

2012