Overview of Electric Vehicle System Architecture

By Vigna K Ramachandaramurthy, Kang Miao Tan, Jia Ying Yong

In the modern age, energy consumers have high expectations for energy supply reliability. Many advanced measures are required to ensure that the power grid is ready for the large integration of Electric Vehicles (EVs). A proper architecture design for an EV charging system is crucial to ensure a reliable power supply for EV demands. Healthy interaction between the EV and power system can greatly upgrade the reliability and sustainability of the power grid, as well as provide ancillary services to the power grid. This technology is denoted as Vehicle-to-Grid (V2G). In the early development stage of V2G, a small-scale framework shall be easy and efficient enough to stimulate a wider adoption of the technology. This also serves as an educational stage in getting the society ready to accept this new concept. When the technology matures, these small-scale V2G building-blocks can be combined and interact via aggregators for smart grid applications. Literature has demonstrated the flexibility of the EV charger when interacting at various scales of the power grid such as smart home, power distribution grid and microgrid.

Smart Home

In a small-scale V2G context, the smart home system usually involves the integration between home appliances, renewable energy sources and energy storages. The incorporation between the EV battery and the smart home system has evolved into a brand new concept, namely the Vehicle to Home (V2H) system. Although smart home usually consisted of an energy storage, the sizing of the energy storage can be greatly reduced or replaced with the introduction of EV to the home environment, without compensating the effectiveness of the system. With the availability of EV battery connected to the smart home, EV can enhance the accessibility of renewable energy to the home electrical appliances. This is done by introducing extra energy storage to the home, where excessive generation of renewable energy source can be stored in the EV battery for later in-home usage. This V2H concept is technically and financially viable to be implemented. Similar concept is also applicable to small-scale office or commercial buildings.

Power Distribution Grid

The EV framework for operation and management becomes essential and the EV aggregator agent will act as the medium between the distribution system operator and participating EVs. From the power system viewpoint, the EV aggregator is seen as a virtual energy storage which can provide ancillary services or serve as controllable loads. This aggregated interaction opens up potential services in the electricity market with appropriate energy tariff and policy. Various EV system architectures in the scale of power distribution grid can be found in literature. It has been recently proposed a grid–connected EV fast charging station, with auxiliary supply from Photovoltaic (PV) solar panels, and Energy Storage System (ESS), all to be connected to a medium voltage DC busbar. An EV fast charging station usually requires a high power charger, which can be very costly. A grid–connected EV ultrafast charging framework based on the Modular Multi–port Power Electronic Transformer Cascaded H–Bridge (M2PET–CHB) concept may eliminate the need of high power components. Multiple and simultaneous EVs charging were achieved by the multi–port parallel–connection configuration used in the EV charging station.

The optimal placement and sizing of EV charging station is an important factor to maximize the potential contribution of EV to the power distribution grid. Typically, this is achieved once the driving pattern of an area is established. Researches have proposed optimization algorithms that determined the optimal sitting and sizing of EV charging station with the aim to reduce investment cost and maximize the power grid reliability. Furthermore, the implementation of energy management for large-scale of grid-connected EVs is crucial in the V2G application. Many optimal scheduling algorithms that determined the real time active and reactive power flow of EVs has been introduced in the literature. These coordinated EV charging schemes had the aim of achieving power grid objective, such as frequency regulation, reduction of losses, spinning reserve procurement, profit maximization and power grid peak load shaving.

Microgrid

Microgrid is developed to integrate the power grid with the distributed sources, energy storages and loads, for both islanded and grid–connected operations, thus enabling independent electricity management and system reliability. From a broader perspective, large-scale of EV penetration will provide a relatively large energy storage capacity to the microgrid, which provides support and services to the grid. A DC microgrid system that combined a DC traction system and EVs, as proposed recently by some researchers, would ensure energy support through the EV batteries to prevent voltage drop in the DC traction system at the start-up and acceleration periods of a train. And vice versa, EVs can recover braking energy and stabilize the system voltage as the train decelerates. Another approach proposed a framework that can be fully supported by the renewable energy sources during the off–grid islanded mode. The EV and renewable based system consisting of a solar panel and wind turbine as energy sources, battery pack as the energy storage, as well as the EVs as the loads and energy storages.

Conclusion

The architectures of the EV charging system shall correlate to the application and ancillary services. With proper planning and implementation of EV aggregated interaction, numerous services can be provided by the EV fleets to the power grid while ensuring the reliability of the power grid. These ‘mobile energy storage’ with aggregators which benefit the energy consumers and power utilities will be the next revolution in the electrical power grid.

Vigna K Ramachandaramurthy

Vigna K Ramachandaramurthycompleted his Bachelors Degree and PhD at the University of Manchester Institute of Science and Technology (UMIST), UK in 1998 and 2001 respectively. He has worked as an electrical engineer in a large electrical utility in Malaysia, with stints in the transmission and distribution subsidiaries and power plant. He is presently a Professor in the Institute of Power Engineering, Universiti Tenaga Nasional (UNITEN), Malaysia. Prof Vigna has received many awards for research and leadership such as the IET Mike Sargeant Award, Institution of Engineers Malaysia (IEM) Young Engineers Award and the IET Malaysia Engineers Award. He has served in the IET Council, IEM Council and the IEEE PES Excomm in Malaysia.

Prof Vigna advocates industry based research. He heads the Power Quality Research Group in UNITEN with 28 researchers under his supervision at the moment. The Group conducts numerous research and consultancy projects in South East Asia. His area of interest includes power systems related studies, smart grid, renewable energy, energy storage, power quality and electric vehicle. He is the consultant to many renewable energy projects and the RE industry in Malaysia and South East Asia. He has conducted the technical feasibility for more than 300 renewable energy plants in Malaysia, in the areas of hydro, solar PV, biomass, biogas, wind and energy storage. He was the principal consultant to the government and utility to formulate and develop the technical guidelines for grid-interconnection of solar PV and distributed generation in Malaysia.

Kang Miao Tan

Kang Miao Tan (S’15) received her B.Eng.(Hons.) degree in Electrical Power Engineering and M.Eng. degree in Electrical Engineering from National Energy University (UNITEN), Malaysia in 2011 and 2016, respectively. She is currently working toward her Ph.D. degree in Electrical Engineering from National Energy University (UNITEN), Malaysia. Her employment experience includes working as an Electrical Project Engineer in the industry. She has been a Research Engineer in the Power Quality Research Group since 2013. Her research interests include vehicle to grid, optimization, smart grid, power electronic converter and power system.

Jia Ying Yong

Jia Ying Yong (M’15) received his B.Eng.(Hons.) degree in Electrical Power Engineering and Ph.D. degree in Electrical Engineering from National Energy University (UNITEN), Malaysia in 2011 and 2017, respectively. He works as a Senior Lecturer in Department of Electrical Power Engineering, College of Engineering, National Energy University (UNITEN), Malaysia. He worked as a Research Engineer in the Power Quality Research Group and has participated in many consultancy projects. His current research interests include grid-connected electric vehicle, smart grid technologies, power electronics, power system studies and experimental applications.


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