Analysis and mitigation of the impacts of integrating fast-charging stations on the voltage fluctuations

Abstract

As the number of electric vehicles increases, fast charging becomes a necessity in the electric service stations; not only to reduce the charging and waiting times for electric vehicles whether in service or in a queue, but also to increase their commercial benefits by increasing their utilization rates. Fast charging stations are characterized by their high-power consumption from the electric grids to fulfill these aforementioned aims. Times and periods of that consumption are indeterminate due to several uncertain parameters that are inherent in the electric vehicles charging process, such as their numbers, their battery capacities, their state-of-charge levels at time of arrivals, and their time of arrivals, which may all lead to a degradation in the quality of electric power delivered to the customers. The research presented in this thesis focuses on the impacts of fast charging stations on three power quality phenomena, namely voltage magnitude variations, voltage unbalance, and voltage fluctuation. The Markov Chain Monte Carlo is proposed to estimate the required energy from each fast charging station when it is utilized to charge the electric vehicles, considering their stochastic parameters. Two charging methods are implemented in this work: charging with an estimated output power and charging with an actual output power. The results reveal that the impact of fast charging stations on voltage fluctuation by either of these charging methods can lead to light flicker. When the estimated output power is utilized, the light flicker is higher compared to when the actual output power is utilized. When the operation of Fast Charging Stations causes a voltage fluctuation and light flicker, the FCSs may get disconnected which results in a financial loses represented by the FCS downtime. The FCS downtime can be avoided by mitigating the voltage fluctuation and light flicker. Several flicker mitigation devices are analyzed and compared based on different criteria. The comparison reveals that distribution static compensators considers the cheapest mitigation device, according to the cost per kVAr basis and the total annual equivalent cost. Besides, to mitigate the impact on the voltage and light flicker, a novel smart charging is proposed in this study in which customers can select one of three charging services available in the fast chargers: premium, regular, or economic charging power. The charging power is selected upon customer priority toward the time and cost which offers less control than those currently available in the literature. The proposed smart charging preserves the balance of customer's value of time and value of cost. The proposed smart charging achieves a tremendous reduction in the cost of mitigation the voltage fluctuation and light flicker. Annual cost of the proposed smart charging is less than the annual cost of distribution static compensators by a minimum of 90% to a maximum of 99 %. The proposed smart charging offers a compromise solution to satisfy several stakeholders with different interests. Thus, equipment of system’s operator, investor of fast charging station, nearby customers, and owners of electric vehicles will not be impacted by integrating the fast charging station.