The pre-step to develop EV charging station infrastructure in QU is to simulate the distribution system of the campus using a simulation software, which in this case is the ETAP software. The ETAP software is an analytical engineering software specializing in the analysis, simulation, monitoring, control, optimization, and automation of electrical power systems [1]. The first step should be the load-flow analysis. After running the load flow for the peak-load scenario, the grid power losses are calculated and the min and max voltage and rated power violations are checked. Then, the spare power capacity available in each substation is calculated. The next step is to select the appropriate EVCS configurations, types, and numbers to add them to the distribution system as additional loads, in order to determine the optimal sizes and locations of these EVCS. For cases where there the existing distribution system cannot support that additional amount of EVCS load because of maximum transformers or feeder cables rating limitations or excessive power losses and voltage drop, a PV installation will be added and integrated into the distribution system as a Distributed Generation (DG). The PV installation will decrease the power flow from the main station and hence decrease the power losses and improve the voltage profile.
Load-Flow Analysis
ETAP software is one of the most efficient load flow analysis software tools available in the market today. The software is allowing to create a load flow module with ease and obtain a precise and reliable result, by using built-in features such as result analyzer, automatic device evaluation, and warnings [2]. The software calculates voltage in all buses, power factor in each branch, current, and power flows throughout the electrical system. It can perform analysis on both loop and radial systems. Besides, it gives the user the option to choose from a different calculation method, which is Newton-Raphson, fast decoupled, and accelerated Gauss-Seidel to achieve efficient and accurate calculation [2].
The Newton-Raphson calculation method is this case since it requires a smaller number of iterations to reach convergence, it has quadratic convergence characteristics, and the number of iterations is independent of the size of the system [2]. The Newton-Raphson method formulates and iteratively solves the equation (1) [3].
Where: J1, J2 , J3,and J4 are the Jacobian matrix elements. ΔP is the specified bus real power mismatch vector between the specified value and the calculated value. ΔQ is the specified bus reactive power mismatch vector between the specified value and the calculated value. ΔV represents bus voltage magnitude, and Δδ represents angle vectors, in an incremental form.
PV Power System Design
The ETAP software permits to model and size, discrete solar photovoltaic panels, grid-connected inverters, system grounding, and solar combiners and collector systems. The main issue with the implementation of the PV system is the area, so the number of PV panels is limited to the empty areas on the campus. After choosing the optimal location where the PV panels can be installed, the number of PV panels in a specific area can be calculated by using equation (2).
The output of the PV panels is direct current, so to connect the panels to the grid, an inverter is required. The inverter maximum input power should be bigger than the maximum PV panels output power. The number of inverters connected to the PV panels van be calculated by equation (3), where Po is the output power for each PV panel.
Besides, the PV panels should be connected in series and parallel, which will give suitable voltage and current to connect them to inverters. The series connection of PV panels affects the total voltage that should not exceed the inverter voltage input, as shown in equation (4).
The parallel connection of PV panels affects the current that should not exceed the input inverter current as shown in the equation (5).
Also, the total number of PVs in one array should be calculated using equation (6).
[1] “Electrical Power System Analysis & Operation Software,” ETAP, [Online]. Available: https://etap.com/. [Accessed 20 1 2020].
[2] A. H., T. H. and S. R., “Comparison of Newton Raphson and Gauss Seidel Methods for Power Flow,” international journal of energy and power engineering, vol. 12, 2018.
[3] M. Ghiasi, “A Detailed Study for Load Flow Analysis in Distributed Power System,” International Journal of Industrial Electronics, Control and Optimization , vol. I, pp. 153-161, 18 December 2018.