Researchers at the Indian Institute of Technology, Guwahati have developed optimised control schemes for active power distribution networks that can enable coordinated operation of photovoltaic power generation and electric vehicle charging stations. The research was recently published in the prestigious journal of 'Sustainable Energy, Grids and Networks', and will help regulate voltages generated by intermittent photovoltaic (PV) systems besides paving a way for electric vehicles to participate in the active power distribution scheme. According to officials, electric vehicles (EVs) are being increasingly considered the solution to carbon emissions from the transportation sector.
The sustainability of EV can be enhanced if the power used to charge these vehicles is also based on renewable energy sources such as solar energy. However, solar energy is intermittent, which leads to voltage fluctuation problems in the power distribution networks.
"EV charging is uncoordinated at present, which leads to under-voltage of the distribution networks, and associated efficiency loss, they said. A coordinated control approach for power distribution system is required in order to derive maximum benefits from renewable power generation and electric vehicle power sourcing. PV and EV inverters need to work in coordination with other Voltage Regulating Devices (VRD) to regulate the system voltages," said Sanjib Ganguly, Associate Professor, Department of Electronics and Electrical Engineering (EEE), IIT Guwahati.
"We have developed an optimisation-based coordinated voltage control approach of power distribution networks to mitigate the overvoltage and under-voltage problems due to high PV generation and high EV charging, respectively. The research team has developed a three-stage model predictive control (MPC) approach to schedule charging of EVs and other devices," he added.
The three stages involve---coordination of the volt-var devices in two different time scales, reception of the reactive power setpoints by the local controller, and EV charge scheduling in accordance with the balance between the operating cost and customer satisfaction.
"Our three-stage model helps in maintaining bus voltage magnitudes and state-of-charge (SOC) of EV battery within safe limits with minimal usage of control resources and cost of electricity consumption," said research scholar Arunima Dutta.
The approach developed by the IIT Guwahati team also provides a framework for the transition from passive power distribution to active. Both solar power generation and EV can enable the transition of power distribution from a passive state (unidirectional flow of power from the grid to the consumer), to an active system wherein there is bidirectional flow of power from the grid to the point of use, and vice versa.
"For example, while the grid-to-vehicle (G2V) model is pretty straightforward, wherein a vehicle is charged by power supplied by a grid, the reverse – vehicle-to-grid (V2G) enables energy to be pushed back to the power grid from the battery of an electric car.
"The model developed by us provides a framework of optimal G2V and V2G operation of EVs by keeping the voltages of each node of a distribution network within allowable upper and lower limits. The charging/discharging of EVs is optimally scheduled with respect to the real-time electricity pricing," said another researcher Chandan Kumar.
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