Browsing by Author "Torres, Esther"
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Item New energy bound-based model for optimal charging of electric vehicles with solar photovoltaic considering low-voltage network's constraints(2021-07) Felipe Cortés Borray, Andrés; Garcés, Alejandro; Merino, Julia; Torres, Esther; Mazón, Javier; Tecnalia Research & InnovationThis paper introduces a linear programming (LP)-based optimisation method of charging electric vehicles (EVs) in a decentralised fashion. It exploits the available photovoltaic (PV) power to charge EV batteries while maintaining the low-voltage (LV) network within its operational limits. A new energy-bound model is implemented in order to meet the connected EVs energy requirements. This model highlights two main aspects: first, the proposed formulation seeks to compute both the upper and lower energy boundaries from the arrival energy and no from zero. Second, the charging power is dynamically adjusted by combining a fixed and variable charging rate to assure the technical limits of the network. This means maximising power delivered to all EVs for a given period by optimising the charging rate of each EV connected. Besides, a network sensitivity analysis technique is developed to manage voltage and loading constraints. The accuracy of the proposed linear approximation was tested simulating two cases (moderate and high penetration level of PVs and EVs) on a real LV feeder. Results over a set of simulations for winter and summer seasons demonstrate that this method can be effectively implemented as a charging strategy and for energy planning studies.Item Optimal coordination of electric vehicle charging and photovoltaic power curtailment in unbalanced low voltage networks: An experimental case: An experimental case(2022) Cortés Borray, Andrés Felipe; Rauma, Kalle; Torres, Esther; Tecnalia Research & Innovation; POWER SYSTEMSThis study introduces a quadratic programming-based optimisation method to coordinate electric vehicle (EV) charging and photovoltaic (PV) curtailment in unbalanced low voltage (LV) networks. The proposed model is defined as a convex model that guarantees the optimal global solution of the problem avoiding the complexity of non-linear models and surpassing the limitations of local solutions derived from meta-heuristics algorithms reported in the literature. The coordination is carried out through a centralised controller installed at the header of the LV feeder. The objective of the proposed strategy is to minimise the power curtailment of all PV systems and maximise the power delivered to all EVs by optimising at every time step a suitable setpoint for the PV units and the charging rate of each EV connected without surpassing network constraints. A new energy-boundary model is also proposed to meet the energy requirements of all EVs, which is based on a recurrent function that depends on the arrival-and-desired energy states of the vehicle to compute its charging trajectory optimally. The effectiveness of the proposed coordination strategy was successfully proven through three scenarios in a laboratory environment, making use of two commercial EVs and a PV inverter in a Power Hardware-in-the-Loop setup.Item Optimal coordination of PV active power curtailment and evs charging among aggregators(2020-10-15) Borray, Andrés Felipe Cortés; Merino, Julia; Torres, Esther; Mazón, Javier; Tecnalia Research & InnovationWith the growing adoption of electric vehicles (EVs) and residential photovoltaic (PV) systems around the world, the distribution system operators (DSOs) are facing several technical challenges on their network planning and operation, particularly on low-voltage grids. As the aggregators are intermediary actors at that system level, they are a promising figure to coordinate these devices in an aggregated manner to help to mitigate adverse effects like overloading of network assets. However, to do so, proper coordination techniques among these entities and the DSO should be developed to avoid further investments in new network assets. In this context, a centralised coordination strategy among aggregators at the DSO level is proposed. By employing a linear programming model, the optimal export limit of PV and charging profile for each aggregator is dictated by the DSO, maintaining the operational limits of the network assets. A case study on two aggregators with moderate and critical penetration levels was carried out. Results show that, by controlling the aggregated export limit of PV power and the aggregated charging rate of EVs, high penetration levels can be integrated into current networks with minor or no need for reinforcing network infrastructure.Item A review of the population-based and individual-based approaches for electric vehicles in network energy studies(2020-12) Cortés Borray, Andrés Felipe; Merino, Julia; Torres, Esther; Mazón, Javier; Tecnalia Research & InnovationThe growing trend of introducing electric vehicles (EVs) into power systems to reduce the environmental emissions in the transport sector is gaining significant attention among electrical power system agents for two reasons: the potential grid services the EVs can offer in an aggregated manner and the possible undesirable effects of massive integration in grid operation that can increase the requirement for investment in new assets. In this context, the aggregator is the representative entity that needs to maximise the benefits in the management of these sizeable quantities of vehicles while fulfilling the requirements of grid services requested by the distribution system operator. In this study, we review the concept of EV aggregators and their potential services to the distribution network. Several studies related to EVs aggregation modelling have been analysed and classified into three groups: individual-based, population-based, and hybrid approaches. We present the current status of EVs aggregation modelling as well as future research trends. Furthermore, we discussed the performance comparison of EVs models from several manufacturers utilised in network integration studies, likewise the most relevant databases and surveys. Finally, we arranged and annexed the most relevant mathematical expressions of the reviewed approaches, thereby simplifying the comprehension of the methods.