Voltage-Dependent Load-Leveling Approach by Means of Electric Vehicle Fast Charging Stations

Abstract

Intermittent generation and load demand are one of the major challenges for grid operators. Caused for example by renewables power variability or electric vehicle charging, it can create mismatches between the realtime and forecasted demand, affecting frequency regulation. To alleviate this mismatch, operators have to resort either on the balancing market or on extensive use of energy storage systems, which increases operation costs. This paper introduces a load levelling approach exploiting the voltage dependency of the loads. With a controlled reactive power injection, the converters of fast charging stations can influence the voltage profile, and consequently the power consumption of voltage-dependent loads. The approach has two main goals: minimizing the mismatch with respect to the demand forecast and reducing grid losses. Fast charging stations are particularly suited for this approach. Being employed with full capacity for charging only for short-time, their spare capacity can be exploited to apply the load levelling approach. This proposed approach is discussed theoretically and analyzed in a modified distribution network in Northern Germany. Parameters variation analysis has been performed to thoroughly demonstrate the effectiveness of the approach under different load/grid conditions. Its feasibility has been evaluated by means of power-hardware-in-the-loop tests.

A Holistic Review on Advanced Bi-directional EV Charging Control Algorithms

“…Apart from energy trading, EVA can also provide ancillary service to the smart grid, such as frequency regulation [8,29,30,34,45], voltage control [11,15,24,39], and reserve service [4,14] etc. Ancillary services provide the resources the system operator requires to maintain the instantaneous and continuous balance between power generation and load demand in a reliable manner.…”

“…[52] proposed a hierarchical system model to jointly optimize power flow routing and V2G scheduling for providing regulation service. Recently, some work proposed several control mechanisms that utilize the dispatch of EVs [11,15,24,39]. [39] proposed a three-layer hierarchical voltage control framework to mitigate fast voltage violation problems with the dispatch and control of EVs.…”

“…[15] presented an optimization model to flexibly control available PEV battery charging/discharging power based on three-phase power flow and sensitivity approaches. [11] proposed a two-stage centralized approach to level the power mismatch between the demand forecast and the real time demand in medium voltage grids by means of fast charging stations. [24] proposed a novel optimal hybrid control framework to improve the voltage profile of highly unbalanced Distribution Grids by coordinating the injection of reactive power from multiple off-board Electrical Vehicles (EVs) chargers.…”