Recently, because of the increase in the number of connections to Distributed Generation (DG), the problem of lowering voltage stability in the distribution system has become an issue. Reactive power compensators, such as Static Synchronous Compensators (STATCOM), may be used to solve the problem of voltage stability degradation. However, because of the complexity of the distribution system, it is very difficult to select the installation location for STATCOM. Furthermore, when installed in the wrong location, economical efficiency and availability problems may occur. This paper proposes a Virtual STATCOM Configuration and Control method that would operate like a single STATCOM based on multiple DGs connected to the system. The proposed Virtual STATCOM has the merit of being economical by using existing facilities without adding new power facilities, and it solves the problem of the difficulty of selecting the installation location because of the complexity of the distribution system. In addition, while the conventional STATCOM uses an independent control method in consideration of the power quality of the access point, the Virtual STATCOM performs the Point of Common Coupling (PCC) power quality compensation using the integrated control of multiple DGs connected to the system. In the proposed method, the Virtual STATCOM integrated control algorithm is configured by adopting linear programming, and the compensation is performed while considering the distance between DG and PCC, the inverter’s rated capacity, and the power generation. The performance of the Virtual STATCOM power quality compensation was verified using MATLAB/SIMULINK and Real Time Simulator (OPAL-RT).

A novel approximation-free differentiator-based output-feedback controller for uncertain large-scale systems (LSSs) is proposed. The considered LSS has nonautonomous and nonaffine-in-thecontrol subsystems which is yet to be tackled for decentralized output-feedback controller in the previous researches. The controller adopts a higher-order switching differentiator that can track the time-derivatives of a time-varying signal asymptotically. Through the differentiators, time-derivatives of output tracking errors are estimated and unstructured uncertainties in the controlled subsystems are compensated. The proposed decentralized output-feedback control formulae and the stability analysis are relatively simple in comparison to the previously proposed decentralized controllers. In this case, approximators such as fuzzy systems or neural networks are not required. The proposed controller guarantees that the tracking errors of the subsystems are asymptotically convergent to zeros and all the signals involved in the closed-loop systems are bounded.

A novel decentralized output-feedback controller is proposed in this paper for large-scale uncertain general nonautonomous nonlinear systems without prior knowledge of the input gain's sign. The subsystems are considered to be completely unknown and nonautonomous, except for their known full relative degree. The proposed controller uses a higher-order switching differentiator to estimate the time-derivatives of the output tracking error, resulting in a low-complexity output-feedback prescribed performance controller that compensates for uncertainties, including high-frequency gain sign and unstructured uncertainties. It is mathematically proven that the output tracking error and its time-derivatives are all maintained within the prescribed regions. To demonstrate the effectiveness of the proposed controller, numerical simulations of two interconnected inverted pendulums are conducted. To the best of the authors' knowledge, this paper presents the first results on this problem.INDEX TERMS Large-scale nonlinear system, decentralized controller, prescribed performance control, unknown control sign.