Contents lists available at ScienceDirect Electric Power Systems Research journal homepage: www.elsevier.com/locate/epsr A modified backward and forward sweep method for microgrid load flow analysis under different electric vehicle load mathematical models Y. Kongjeen a , K. Bhumkittipich a, ⁎⁎ , N. Mithulananthan b , I.S. Amiri c,d, ⁎ , P. Yupapin c a Department of Electrical Engineering, Faculty of Engineering, Rajamangala University of Technology Thanyaburi,Thanyaburi District, Pathum Thani, 12110, Thailand b Power and Energy Research Group, School of Electrical Engineering and Information Technology, University of Queensland, Brisbane, Australia c Computational Optics Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam d Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam ARTICLE INFO Keywords: Electric vehicle Exponential load Modified backward–forward sweep method Power system Voltage-dependent load ZIP ABSTRACT A power flow analysis under different electric vehicle (EV) load models based on the modified backward and forward sweep method is presented. Voltage-dependent loads (VDLs) were used to analyze the total power loss and load voltage deviation (LVD) under different EV load models and the general load of the electrical power system. The VDL was defined in the backward stage where the voltage ratio was between bus voltages per nominal voltage. The IEEE 33 bus radial distribution system was selected to be the test system. The EV pene- tration level was defined as 26.88% compared to the base case of constant power (P). The simulation results showed the impact levels from EV load models to the grid based on the traditional method, with impact levels from high to low being for polynomial load (EVI), constant current load (EVIII), and VDL (EVII) models, re- spectively. In particular, the highest impact for EVI was in scenario 4 (D), where the total active power loss, total reactive power loss, and LVD were 3.45%, 3.47%, and 3.36%, respectively. Therefore, the EV load model was one important factor to select for solving the power flow of the grid. Moreover, the position and size of the EV load could be considered in the optimal condition for reducing the impact to the grid. However, energy man- agement will become a key challenge for supporting the high penetration of EVs in the near future. 1. Introduction Recently, the increasing numbers of electric vehicles (EVs) have provided a new integrated load on the electrical power system. Ultimately, internal combustion vehicle engines (ICVEs) could be re- placed by EVs, because ICVEs have a high impact on the environment, use expensive fuel, and make a significant carbon footprint [1]. Ad- vancement of power electronics and battery technology has been driven by new materials and algorithms for supporting EVs, as presented in Refs. [2–4]. Therefore, advancement of EV technology has been of in- terest for studying and investigating the impact of EVs on the electrical power system. Furthermore, the high penetration of EVs has been considered an optimal condition for planning and reducing power system instability. In summary, EV load information is needed to ana- lyze any effect on the power system and assess the impact from EVs. Gathering this information would enable planning for the improvement of the electrical power system in the near future. Energy demand profiles have been affected by the large number of the EVs connected to the grid; in the same way, peak shaving of power demand has increased and changed from conventional demand, as presented in Refs. [5,6]. Accordingly, the peak demand impact of EVs can be considered to manage and reduce the peak demand levels of the grid. The high impact of the EVs in their fast charging condition has affected the electrical power system and induced power system oscil- lations that can compromise stability, and this has evaluated by com- paring between the EV loads and the conventional load (Z, I, P) on a Single Machine Infinite Bus (SMIB). The results showed that power system oscillations from EVs have greater impact than conventional loads in terms of the low percentage damping ratio [7]. Therefore, the effect of EVs should be investigated to solve many buses of the electrical power system. When EVs are charging and discharging in a resident place, they are connected to the low-voltage level of the electrical power system. Especially, the EV charging process for many EVs in- creases the voltage imbalance and affects the voltage difference be- tween phases [8,9]. Moreover, high numbers of EVs connected to the power system have been used for investigating the EV load. The https://doi.org/10.1016/j.epsr.2018.10.031 Received 31 March 2018; Received in revised form 19 September 2018; Accepted 25 October 2018 ⁎ Corresponding author at: Ton Duc Thang University, Ho Chi Minh City, Vietnam. ⁎⁎ Corresponding author. E-mail addresses: krischonme.b@en.rmutt.ac.th (K. Bhumkittipich), irajsadeghamiri@tdtu.edu.vn (I.S. Amiri). Electric Power Systems Research 168 (2019) 46–54 0378-7796/ © 2018 Elsevier B.V. All rights reserved. T