With the rapid development of power electronics, Flexible AC Transmission Systems (FACTS) devices have been proposed and implemented in power systems. This research mainly investigates the robust coordinated control of FACTS devices and traditional power system controllers in large power systems. The following objectives have been achieved:
 1. FACTS modeling and controller design: FACTS devices are modeled using the current injection method. Linear and non-linear methods for the FACTS damping controller design are developed.
 2. Optimal choice and allocation of FACTS devices: Using the genetic algorithms, the locations of the FACTS devices, their types and rated values are optimized simultaneously. The objective function, which consists of the investment costs for FACTS devices and the generation costs, is minimized. 3. Adaptive FACTS transient controller design using ANFIS technology: This objective deals with the development of fuzzy adaptive FACTS transient stability controller. Furthermore, by means of Adaptive Network based Fuzzy Inference System (ANFIS) technology, the fuzzy controller parameters are optimized. 4. Simultaneous coordinated tuning of FACTS damping controller and conventional Power System Stabilizers (PSSs): Using the linearized power system model and the parameter-constrained non-linear optimization algorithm, interactions among PSS and FACTS damping controllers are considered. The controller parameters are optimized simultaneously to achieve a global optimal damping behavior. 5. Robust FACTS loop-shaping Power Oscillation Damping (POD) controller design in multi-machine power systems: By applying the model reduction and modern robust loop-shaping control technique, the FACTS robust loop-shaping POD controller is realized. This controller exploits the advantages of both conventional loop-shaping and modern H infinite robust control technique. Moreover, it is a decentralized approach and suitable for FACTS controller design in real large power systems. 
Die Dissertation erscheint parallel im Logos-Verlag , Berlin mit der ISBN 3-8325-0570-9

Robust Coordinated Control of FACTS Devices in Large Power Systems

The present invention is concerned with the combined voltage or power flow control and damping of electromechanical oscillations in an electric power system (2) by Flexible AC Transmission System (FACTS) devices (20) or High Voltage DC (HVDC) transmission devices. To this end, information about a state or operating point of the power system is generated from suitable second system signals (y2) and a control parameter (cp) of a FACTS controller (1) is derived therefrom. The control parameter and a first system signal (y1) are used in the calculation of a control command (u) defining the settings of the FACTS device. Following a change in the state of the power system such as a change in the topology of a transmission network, poorly damped or even unstable oscillations are avoided by appropriate re-tuning of the control parameter of the damping or stabilizing equipment.

Damping electromechanical oscillations in power systems

Power System Stabilizers (PSS) are generally employed to damp electromechanical oscillations by providing auxiliary stabilizing signals to the excitation system of the generators. But it has been found that these Conventional PSS (CPSS) do not provide sufficient damping for inter-area oscillations in multi-machine power systems. Thyristor Controlled Series Capacitor (TCSC) has immense potential in damping of inter-area power swings and in mitigating the sub-synchronous resonance. In this paper Improved Harmony Search Algorithm (IHSA) has been proposed for coordinated design of multiple PSS and TCSC in order to effectively damp the oscillations. The results obtained by using IHSA on WSCC 3-machine, 9-bus system are found to be superior compared to the results obtained using Bacterial Swarm Optimization (BSO) algorithm. The damping performance of conventional PSS and TCSC controllers is also compared with coordinated design of IHSA based PSS and TCSC on New England 10-machine, 39-bus system over wide range of operating conditions and contingencies. To demonstrate the effectiveness of the proposed technique the results obtained on this test system are also compared with the results obtained with Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Harmony Search Algorithm (HSA) and Bacterial Swarm Optimization (BSO).

Coordinated design of power system stabilizers and TCSC employing improved harmony search algorithm

This paper presents a review on applications of Flexible AC Transmission Systems (FACTS) controllers such as Thyristor Controlled Reactor (TCR), Thyristor Controlled Switched Reactor (TCSR), Static VAR Compensator (SVC) or Fixed Capacitor‐ Thyristor Controlled Reactor (FC‐TCR), Thyristor Controlled Series Capacitor (TCSC), Thyristor Controlled Switched Series Reactor (TSSR), Thyristor Controlled Brakening Reactor (TCBR), Thyristor Controlled Voltage Reactor (TCVR), Thyristor Controlled Voltage Limiter (TCVL Thyristor Controlled Switched Series (TSSC), Thyristor Controlled Phase Angle Regulator (TC‐PAR) or Thyristor Controlled Phase Shift Transformer (TC‐PST), Static Synchronous Series Compensator (SSSC), Static Synchronous Compensator (STATCOM), Distributed Static Synchronous Compensator (D‐STATCOM), Generalized Unified Power Flow Controller (GUPFC), Unified Power Flow Controller (UPFC), Inter‐link Power Flow Controller (IPFC), Generalized Inter‐link Power Flow Controller (GIPFC),and Hybrid Power Flow Controller (HPFC), Semi‐ conductor Magnetic Energy Storage (SMES), Battery Energy Storage (BESS), in power system environments for enhancement of performance parameters of power systems such as reactive power support, minimize the real power losses, improvement in voltage profile, improvement in damping ratio of power systems, provide the flexible operation and control etc. Authors strongly believe that this survey article will be very much useful for the researchers, practitioners, and scientific engineers to find out the relevant references in the field of enhancement of performance parameters of power systems by different FACTS controllers such as series, shunt, series‐shunt, and series‐series connected FACTS controllers are incorporated in power systems. This article is very much useful for researchers for further research work carryout in regarding with the application of FACTS controllers in power system environments for enhancement of performance parameters of systems.

Introduction to FACTS Controllers: A Technological Literature Survey

In this paper, conventional lead-lag power system stabilizer (CPSS) is designed to damp electromechanical oscillations. CPSS parameters settings are computed using linear control theory. A new technique based on particle swarm optimization PSO is proposed to optimize the parameters settings of CPSS. The problem is formulated as an optimization problem, the objective is to compute the optimal parameters settings such that damping ratio maximized as much as possible. The performance and robustness of optimized CPSS (OPSS) is then, tested on 9-bus multi-machine system under normal operating conditions, heavy loadings and response to three phase short circuit. Eigenvalues results and nonlinear time domain simulation show the effectiveness and robustness of the proposed OPSS over CPSS under different proposed cases.

Design and parameters optimization of power system stabilizer to improve power system oscillations

This work deals with the simultaneous coordinated tuning of the FACTS (flexible AC transmission systems) POD power oscillation damping) controller and the conventional PSS (power system stabilizer) controllers in multimachine power systems. Using the linearized system model and the parameter-constrained nonlinear optimization algorithm, interactions among FACTS controller and PSS controllers are considered. Furthermore, their parameters are optimized simultaneously. Simulation results of multimachine power system validate the efficiency of this new approach. The proposed algorithm is an effective method for the tuning of multicontrollers in large power systems.

L.J. Cai

Papers

Simultaneous coordinated tuning of PSS and FACTS controller for damping power system oscillations in multimachine systems