Project 12:
Electric Vehicle Interaction at the Electrical Circuit Level

Objective

Investigate the effect of electric vehicle adoption on the circuit level utility distribution grid for residential application by determining the impact of electric vehicle charging and discharging to the grid.

Bried Description

This project has evaluated the impacts of electric vehicles (EVs) on the electricity distribution grid. After conducting a literature review on the current state of EV charger technology and on over-voltage mitigation, a transient time domain model of a sub-circuit service area has been developed. This model integrates EV charging and PV load generation into the utility grid and utilizes EV charging as a means of mitigating transient over-voltages (TOVs) in various scenarios. A novel methodology for early detection of TOVs demonstrates that the technical topology of the charging station combined with the connected load of the EV can be used to prevent and eliminate over-voltage peaks. This effect can be used to improve the response time and reliability of inverter-based islanding detection and, thus, increase grid reliability. The proposed over-voltage detection and prevention methodology is currently being verified for practicability with measured residential data sets. The project results are presented in three published reports. Continuing work involves collecting residential data to understand load variability and disaggregation of load.

Describe Implementation of Research Outcomes

In the project’s initial stages, a literature review was conducted on the current state of EV charger technology, focusing on power ratings, control capabilities, embedded sensors, and international standards. The results of this study along with various categorizations of charging station standards are presented in the report Current State-of-the-Art of EV Chargers.

A second literature review was conducted on over-voltage mitigation at the sub circuit level of electricity grids with high photovoltaic (PV) to load ratios. The results of this work is presented in the  report Transient Over-Voltage Mitigation and its Prevention in Secondary Distribution Networks with High PV-to-Load Ratio. These reports are referenced below and are available on the EVTC website.

Following the reviews, a transient time domain model of a sub circuit service area was developed. This model includes EV charging and integrated PV load generation. The model utilizes EV charging as a means of mitigating transient over-voltages (TOVs) in various scenarios. The research also developed a novel methodology for early detection of TOVs. This model has been used to show that the technical topology of the charging station combined with the connected load of the EV can be used to prevent and eliminate over-voltage peaks. This effect can be used to increase the response time and reliability of inverter-based islanding detection and therefore increase grid reliability. A report on the model is referenced below and is “Islanding Detection and Over Voltage Mitigation using Wireless Sensor Networks and Electric Vehicle Charging Stations”.

The proposed over-voltage detection and prevention methodology is currently being verified for practicability with real data sets. The objective of this work is to find further potential solutions that EV charging offers while mitigating transient over-voltages at the sub circuit level during normal grid operation. To collect data for this part of the project, a measurement unit has been designed and developed to record the current of a power line and send the results to a server located at the Renewable Energy Design Laboratory, at the University of Hawaii Manoa. with sample frequency of 1 Hz. The unit has been installed in the residential electrical fuse box. The collected data will be used to understand the load variability and disaggregation of load. A report will be prepared to describe the disaggregation method.

Impacts/Benefits of Implementation

A sub circuit model has been developed that utilizes EV charging as a means of mitigating transient over-voltages (TOVs) in various scenarios. The research also developed a novel methodology for early detection of TOVs. This model has been used to show that the technical topology of the charging station combined with the connected load of the EV can be used to prevent and eliminate over-voltage peaks. This effect can be used to increase the response time and reliability of inverter-based islanding detection and therefore increase grid reliability.

Reports

Schwarzer, V., Ghobani, R., (2015). Current State-of-the-Art of EV Chargers (HNEI Rep. No. HNEI-01-15). Honolulu, HI: Hawaii Natural Energy Institute, University of Hawaii at Manoa.

Schwarzer, V., Ghobani, R., (2015). Transient Over-Voltage Mitigation and its Prevention in Secondary Distribution Networks with High PV-to-Load Ratio (HNEI Rep. No. HNEI-02-15). Honolulu, HI: Hawaii Natural Energy Institute, University of Hawaii at Manoa.

Schwarzer, V., Ghobani, R., (2016). Islanding Detection and Over Voltage Mitigation using Wireless Sensor Networks and Electric Vehicle Charging Stations (HNEI Rep. No. HNEI-08-15). Honolulu, HI: Hawaii Natural Energy Institute, University of Hawaii at Manoa.

Sariri, S., Schwarzer, V., Ghobani, R., (2018). Electric Vehicle Interaction at the Electrical Circuit Level (FSEC Rep. No. FSEC-CR-2077-18, HNEI Rep. No. HNEI-17-18). Honolulu, HI: Hawaii Natural Energy Institute, University of Hawaii at Manoa.