Modelling and Simulation in Engineering

Volume 2016, Article ID 5968943, 7 pages

http://dx.doi.org/10.1155/2016/5968943

## Harmonic Impact of Plug-In Hybrid Electric Vehicle on Electric Distribution System

Department of Electrical, Electronic and Systems Engineering, Universiti Kebangsaan Malaysia, 43600 Bandar Baru Bangi, Malaysia

Received 16 February 2016; Accepted 13 July 2016

Academic Editor: Agostino Bruzzone

Copyright © 2016 A. Aljanad and Azah Mohamed. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

This paper presents the harmonic effects of plug-in hybrid electric vehicles (PHEV) on the IEEE 37-bus distribution system at different PHEV penetration levels considering a practical daily residential load shape. The PHEV is modeled as a current harmonic source by using the Open-Source Distribution System Simulator (OpenDSS) and DSSimpc software. Time series harmonic simulation was conducted to investigate the harmonic impact of PHEV on the system by using harmonic data obtained from a real electric vehicle. Harmonic effects on the system voltage profile and circuit power losses are also investigated by using OpenDSS and MATLAB software. Current/voltage total harmonic distortion (THD) produced from the large scale of PHEV is investigated. Test results show that the voltage and current THDs are increased up to 9.5% and 50%, respectively, due to high PHEV penetrations and these THD values are significantly larger than the limits prescribed by the IEEE standards.

#### 1. Introduction

Currently, there has been a considerable growth of plug-in hybrid electric vehicles (PHEV) integrated in electric power distribution systems. PHEV which are randomly injected into a distribution system would introduce many challenges and impacts on the system. The uncontrolled connection and disconnection of PHEV into a power distribution system will increase harmonic voltage and current distortions [1, 2]. From the power system operation perspective, the large scale integration of PHEV into the grid poses a real challenge. As most of the electric vehicles are fully or partially charged by electricity, it makes them connected to the distribution grid for considerable time duration [1]. Large scale connection of PHEV will cause uncertainty in power system operation. Some studies have shown that without any kind of mitigation the charging of PHEV incurs the electricity grid with additional loads which results in increment of aggregated load during peak hours and hence impacts the overall reliability of the grid [2]. High penetration of PHEV load can give rise to operating conditions which do not arise in traditional power systems and one of the potential issues that need to be addressed involves impact on power quality which includes interruption of service, variation in voltage magnitude, and harmonic distortion in voltage and current [3]. Thus, integration of PHEV may have adverse effect on the distribution network if the penetration is not carefully and systematically planned due to the nonlinear nature of PHEV that generate harmonics which can cause abnormal operation such as increased losses, reduced efficiency, temperature rise, and premature insulation and winding failures. Harmonic currents generated by large number of single phase electronic loads present in a distribution system can cause appreciable harmonic distortion in the grid voltage [4, 5]. The presence of nonlinear electronic loads will cause increasing spectral injectors of low order harmonic currents into the grid [4].

Many studies have been conducted related to the impact of PHEV on the grid during normal charging behavior and also concern the uncoordinated charging behavior of PHEV when connected randomly in the distribution system [6–8]. Previous studies that investigate the impact of PHEV integration on harmonics consider area residential load curve. In the proposed study on impact of PHEV, harmonic effects on a practical residential load shape have been exerted considering two cases: on-peak and off-peak hours during rapid charging. In addition, the impacts of PHEV on other power quality issues like voltage variation and circuit losses are also studied considering the daily load.

The aim of this study is to investigate the impact of PHEV on voltage and current harmonic distortion by performing harmonic analysis on a test system using the OpenDSS software. Harmonic power flow was executed at each harmonic frequency at the given harmonic spectrum associated with the PHEV. Due to the propagation of harmonic currents, the harmonic voltages at all nodes in the system were then captured. In this study, the baseband harmonics are confined to well below the 15th harmonic of the fundamental frequency of 50 Hz (850 Hz). The reason for confinement of the harmonic voltages and currents is based on several factors including the limited bandwidth of the distribution system and also the limited harmonic content of typical distribution system loads.

#### 2. System Modeling

PHEV has been modeled as loads at separate individual phases to take into account the unbalanced three-phase loads and also single phase loads are very common in distribution feeders. For other loads in the distribution system, constant power loads are considered.

##### 2.1. Line Model

For each of the series elements, a set of equations based on the* ABCD* parameters have been used. These parameters relate the sending end three-phase voltages and currents to the receiving end three-phase voltages and currents for each harmonic, which are given byThe* ABCD* parameters of all the elements except the load tap changers (LTCs) are constant. In case of LTCs, these parameters depend on the tap position during the time of operation. The following equations are used to represent the* A* and* D* matrices for each LTC:where represents the change of time operation and , , and are the tap variables with integer values.

##### 2.2. Constant Power Load

The wye-connected constant power loads on a per-phase basis are given as follows [7]:For the delta-connected loads and capacitor banks, line-to-line voltages and currents are required. The equations for voltages and currents which relate line-to-line variables to phase variables are given as follows:

##### 2.3. Modeling of PHEV Load

In this study, PHEV is represented as injected current harmonic source. For harmonic analysis considering current injection method, PHEV load is modeled as a Norton equivalent circuit where the current source represents the harmonic currents injected by nonlinear portion of the load. Figure 1 shows a Norton equivalent model of a load element in OpenDSS with a combination of series* R-L *and parallel* R-L *and the shunt admittance represents the linear load. The linear portion of the load provides a damping element to harmonic propagation. The current source is set to the value of fundamental current times the multiplier defined in the “spectrum” object associated with the load for the frequency being solved. The equivalent shunt admittance can be adjusted by stating the percentage of linear load that is connected as series* R-L *and parallel* R-L *where and are frequency dependent.