Abstract
This study analyzes the primary and secondary frequency controls of the power system. Further, the article discusses the high-level understanding of keeping a selected feeder’s power supply during an upstream fault condition. The Sri Lankan power system is taken as a case study. Due to the high penetration of wind and solar injection to the Sri Lankan power system, the inertia of the system has been reduced drastically. Simulations have been carried out on a single feeder as it is impracticable to install a large battery energy storage system (BESS). The problems of dynamic stability of the current system due to high solar power penetration are analyzed. The repercussions of these problems to the power system are then discussed related to the stability of the system where there is severe machine tripping. Remedial action needed to be taken to increase the power quality of the power system, namely, BESS and supercapacitors are presented. A comparison of the inertia of the current system and the system when conventional power replaces solar power is also analyzed. The article addresses on how fast-active power injection could be used as an uninterrupted power supply to the selected feeder. It also states the fact that in the case of underfrequency load shedding, the feeder will not experience a power outage due to the BESS. However, BESS limitation and cost analysis are not discussed extensively. The results of analysis show that the selected feeder has uninterrupted power even though the grid was disconnected. Further, an approach is also taken to establish the required reactive power to the feeder as well. Method of combining virtual inertia with inverters is discussed here. All simulations conducted were based on real feeders and data.
Highlights
Small power systems are prone to having reductions in their inertia with the increasing penetration of renewable energy and consequent loss of the rotating mass of conventional generation
Simulations were conducted by using a 50 MW battery supply connected to a load center
The battery energy storage system (BESS) was oriented in the downstream, and the BESS was modeled to act as an uninterrupted power supply (UPS) to the feeder
Summary
Small power systems are prone to having reductions in their inertia with the increasing penetration of renewable energy and consequent loss of the rotating mass of conventional generation. De-loading and integration of energy storage are two methods that can be used to control the frequency and the inertia when renewable energy sources (RESs) are present (Dreidy et al, 2017). As the system increases its solar penetration, the system’s rotational masses are being replaced by PV plants which comprise zero inertia. This decreases the strength of the system, and because of that, the angle stability would not be achieved even in a case of a minor fault in the system.
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