David Steen

Effects of Plug-in Electric Vehicles on distribution systems: A real case of Gothenburg

The electric power system is changing and, especially, the electrical distribution system will meet new features. One of the large changes is a transformation of the transportation sector with the use of electricity, with introduction of Plug-in Electric Vehicles (PEVs). This will pose new challenges and opportunities for the electric distribution companies. This paper analyzes the effects of PEVs charging on the local 400 V and 10 kV electric distribution systems in the city of Gothenburg, Sweden, using steady-state power flow analysis. Two different areas representing residential area and commercial area have been simulated for the worst-case scenario, which is simultaneous charging of all the vehicles during the peak load period. The number of PEVs used has been estimated based on the load level at each customer location. The study results have shown that overloading of lines and transformers would occur when simultaneous charging of the vehicles during the peak load period. There would, however, be no problem with the voltage drop at the customers location during PEVs charging. An iterative method is proposed to estimate the maximum number of possible vehicles charging in the distribution system without resulting in any congestion. This method is also applied when one of the feeders is on outage to ensure the N-1 reliability criterion.

Optimal load management of electric heating and PEV loads in a residential distribution system in Sweden

The electrical distribution system is facing major challenges in the near future related to increased electricity consumption, increased amount of distributed generation (DG) and the introduction of plug-in electric vehicles (PEVs). These could require large investments in the distribution system to maintain and operate the system in a secure way. However, the need to reinforce the distribution system can be avoided or postponed if the loads could be managed and controlled in order to reduce the peak load in the system. This paper examines the possibility for such a load management scheme in a residential part of the distribution system in the city of Gothenburg, Sweden. The load management scheme aims to minimize the losses in the system by shifting the heat loads and PEV charging in time without reducing the comfort level of the customers. In addition, a price-based optimal strategy is proposed, assuming dynamic electricity rates, that aims to minimize the electricity cost for the customers. The results indicate that the peak load can be decreased by the proposed load management scheme and that the number of PEVs that can be handled by the distribution system increases. However, dynamic electricity rates can cause increased peak power demand, indicating that either an aggregator or more advanced approaches for the electricity tariffs are needed to cope with the peak power.

Integration of plug in hybrid electric vehicles and electric vehicles - experience from Sweden

Integration of plug in hybrid electric vehicles and electric vehicles (PHEVs and EVs) includes a wide area of topics like grid effects, different charging concepts, charger designs, harmonics from the charger etc. This short paper gives an introduction to ongoing work within this field in Sweden, and shows on research work within the topic at Chalmers University of Technology.

Fast charging of electric buses in distribution systems

The electrification of the public transportation system will likely lead to an increased need of reinforcement in the electrical distribution system. This paper presents an investigation on the impacts of fast charging stations for electric buses on the distribution system. The use the fast charging stations for reactive power compensation (RPC) is presented and the possible benefits for the distribution system is evaluated. The results have shown that by utilizing the charger for RPC, the hosting capacity for electric buses of the distribution system could be increased by up to 13% while network losses could be reduced by approximately 1–2%. However, utilizing the charger for RPC would increase the losses within the converter which could be higher than the gain in network losses. Furthermore the possible benefit depends, to a large extent, on the location of the charge station and the strength of the distribution system.

Cost-benefit analysis of battery storage investment for microgrid of Chalmers university campus using μ-OPF framework

This paper presents a cost-benefit approach for evaluation of battery energy storage (BES) options to be installed in the electrical distribution grid of Chalmers University from the microgrid perspective. The evaluation is based on a multi-period ac optimal power flow model applied for microgrid, which is referred to as the μ-OPF, with the objective function being the total grid operation cost. The model is developed for the real 12 kV grid of Chalmers. The μ-OPF is used as the calculation tool for the cost-benefit analysis where the benefit-to-cost ratios (BCR) of battery options in the grid in a year over the annualized cost of battery are evaluated for various options of battery sizes in the grid. The best location for the battery storage was however determined with the minimum loss criterion. The BCRs demonstrate the cost-effectiveness of the battery in microgrid operation. Battery options considered include both distributed option and a centralized option. It has been found that the best location of battery storage at Chalmers grid is at the point of connection to upstream grid of Gothenburg Energy distribution system for the centralized option. The study results show that the benefit gained from using battery storage increases with the size of battery, and the size with the highest BCR was found to be 2 MWh when considering the grid-connected mode of operation. The optimal size when the grid is in island mode is however dependent on island mode capability.

Using the advanced DMS functions to handle the impact of plug-in Electric vehicles on distribution networks

Integration of Electric vehicles and their impact on power system have been a major topic within smart grid initiatives. It is proven that managing larger amount of loads in form of plug-in Electric vehicles (PEV) is a challenge for operation of low and medium voltage distribution network. The main objective of this paper is to discuss the usage of “Integrated Volt/Var Optimization” function (which is one of main advanced distribution management system (DMS) functions) for handling the larger share of PEV load and reducing their impact on operation of Distribution System (DS). For this purpose, we propose a method for evaluating the impact of PEV charging on steady state operating condition of DS and identifying its possible capacity limitations in case of significant penetration of PEVs. We have applied a stochastic modeling for base EV load and have examined several different scenarios based on charging power and penetration level of PEVs to compare uncontrolled charging with base operation conditions. By presenting the results from our developed Volt/Var Optimization (VVO) engine, it is concluded that DMS functions can support handling of these new operating conditions for DSOs. A real distribution network in south western part of Sweden is used as test system for this study while a set of realistic load profile has been created based on real driving pattern (using the results of national survey from Swedish traffic authority) and actual base load for one year. In this work, the VVO function have been implemented in General Algebraic Modeling System (GAMS) by using a single mixed integer linear programming (MILP) model for the volt-var problem. The results of optimization are system loss and voltage profile along the network in comparison with “base-case” solution.