Third harmonic management and flexible charging for the integration of electric vehicles into the grid
Hernandez, Jorge Eliezer
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Electric vehicle (EV) development has gone into an accelerated pace in recent years to address pressing concerns on energy security, the environment, and the sustainability of transportation. The future market success of EVs is still uncertain, but the current shift in the automotive industry is indicating a possible bright future for EVs. Because of its unique load characteristics, an extensive deployment of EVs will not only bring challenges to power systems, but will enable new opportunities as well. The objective of this work is to address the increased third harmonic currents expected with the introduction of EVs and to explore the potential of leveraging flexible EV charging to increase wind power production. Since EV chargers rely on a nonlinear power conversion process to obtain a controllable DC source from the utility AC supply, it is expected that these devices will aggravate third harmonic current issues. In fact, utility harmonic field data show that, even without EVs, distribution feeders are already experimenting elevated levels of third harmonic currents. To address present and future utility harmonic filtering needs, a practical third harmonic hybrid active filter for medium voltage (MV) applications is proposed. Its design is based on strict utility requirements of cost, reliability, and ease of system implementation. The operation and performance of the proposed filter is verified through simulations and two experimental setups, one tested at 7.2 kV. Furthermore, a system impact study of the proposed filter is performed using actual data for a typical residential/small commercial distribution feeder. Because vehicles remain stationary most of the time, EVs have the potential of being flexibly charged, providing a spectrum of opportunities for system operators. The recent increase in wind power penetration in the U.S. is raising concerns on how to accommodate this stochastic renewable energy resource in day-ahead scheduling operations. In this work, a detailed integrated day-ahead scheduling framework is developed to explore the impact of leveraging flexible EV charging to balance out the variability and uncertainty of wind power generation. It is determined that the full benefits of balancing wind power generation with flexible EV charging may not be achieved in congested power systems. A potential solution based on deploying power routers (PRs) to augment the flexibility of the transmission system is proposed. Simulation results are presented for a test system based on the IEEE 39-bus system.