# Stateflow-Based Energy Management Strategy for Hybrid Energy System to Mitigate Load Shedding
## 3 Modeling of HES Components
### Case Study  
The specific case study concerns on the reliability and availability of electricity supply in an area within Quetta City, a region in Baluchistan, Pakistan (30.1798\({}^{\circ}\) N, 66.9750\({}^{\circ}\) E). The problem is unique because it incorporates the real-time load-shedding scenario that requires intervention from the HES. The load shedding is a condition whereby the electricity supply to a specific area is cut off to allow other areas to fulfill their electric power demand. This is normally scheduled on an hourly basis by the national electric power regulatory authority. The load shedding is necessary due to the acute inadequacy of power generation. In the case of Quetta, the shedding is not expected to reduce in the near future as the electricity demand is growing, while the supply is not coping at the same rate. Despite these difficulties, this region has the tremendous potential of indigenous renewables, particularly solar. Characteristics of high solar irradiance and moderate temperature of Quetta make it an ideal candidate for PV generation. Furthermore, with the high tariff imposed by the utility provider to the customer, a PV system is economically viable. Furthermore, PV installation also has much faster construction times (18 to 24 months); thus, the solution can be realized much earlier compared to building a large conventional power plant.  
To represent the behavior of load shedding, the supply from the utility is plotted in the form of a unit step function [10]. Figure 8a shows the daily power supply schedule of a local distribution feeder of Quetta city for one summer day (14 June 2020) [40]. The off states (depicted on the \(x\)-axis) reflect shedding durations; on average, it is 5 h a day. However, the schedule can differ for the summer and winter seasons. The average load demand profile is required to estimate the amount of electricity being used by the community. In this case study, a local load profile of a small residential community (with limited public facilities) within Quetta city is considered [41]. Two load profiles are considered: one for the summer season (March to August) and the other for the winter season (September to February). The load curves showing the hourly load shape are given in Figure 8b. The daily energy consumption for the summer and winter is 345 and 309 kWh, respectively. The peak power usage is at 26.66 and 23.91 kW for both seasons. Further, the load curve is categorized into two time zones, according to the Pakistan time-of-usage (TOU) tariff. The peak period is from 18 to 22 h, while the remaining 20 h are the off-peak. In order to simplify the observation, it is assumed that the local and grid peak demands coincide with each other.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Parameter** & **Values** & **Units** \\ \hline PV & Rated power & 325 & W \\  & Efficiency & 17.0 & \% \\ ESU & Rated capacity & 1800 & kWh \\  & Efficiency & 100 & \% \\  & Rated power & \(10,20\) & kW \\  & Efficiency & 85.0 & \% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Technical specifications of the HES components.  
Figure 7: Split generator system.  
Regardless of the problems, Quetta has the tremendous potential for indigenous renewables (particularly solar). Characteristics of high solar irradiance and moderate temperature make this region suitable for PV generation. Figure 9 demonstrates the annual climatological data (solar radiation, ambient temperature) of Quetta logged from August 2019 to August 2020, taken from Solcast (solar resource assessment and forecasting data) [32]. The data indicate the mean value of global horizontal irradiance (GHI) of 5503 kWh/m\({}^{2}\)/day.