Advances in Electrical and Computer Engineering Volume 17, Number 4, 2017 Power System Stability Improvement through the Coordination of TCPS-based Damping Controller and Power System Stabilizer Muhammad Arif Sharafat ALI, Khawaja Khalid MEHMOOD, Chul-Hwan KIM College of Information and Communication Engineering, Sungkyunkwan University, Natural Science Campus, Suwon, Republic of Korea sharafat@skku.edu 1 Abstract—To guarantee the secure and reliable operations of power systems through the rapid damping of low-frequency electromechanical oscillations (LFEOs) is the ultimate objective of this study. This paper presents a coordination of a flexible AC transmission system (FACTS) device and power system stabilizer (PSS) to meet this objective, and deals with the design of a damping controller based on a thyristor- controlled phase shifter (TCPS) and a PSS. The proposed design is incorporated in the framework of a single-machine infinite-bus (SMIB) power system. The effectiveness of the proposed design in damping power system oscillations is explored through eigenvalue analysis, time-domain simulations and damping torque contribution. A comparative study on different control schemes, such as with an SMIB including a PSS and an SMIB including a TCPS-based damping controller is also carried out. The obtained results prove the superior performance of the proposed design in improving the stability of the given power system. All the digital simulations are performed using MATLAB/ SIMULINK. Index Terms—damping, flexible AC transmission systems, phase shifter, power system control, power system stability. I. INTRODUCTION Modern electrical power systems are complex nonlinear systems and operate under stress due to overloading to meet the increasing electrical power requirements of the consumers with a suitable quality and price. Over the years, assurance of stability and performance of the power systems has gained great importance in power system operations. Low-frequency (0.1–2.0 Hz) electromechanical oscillations (LFEOs) confine the steady-state power transfer limits of the power systems. Poor damping of LFEOs places a question mark on the secure and reliable operations of the power systems. Power system stabilizers (PSS) are installed with synchronous machines [1] to damp out LFEOs, but their reliability is only effective for small trips around the operating point. The application of power electronics-based controllers, such as flexible AC transmission systems (FACTS) devices, in power systems not only enhances the power transfer limits [2] of transmission lines but also improves the control capability [3–4] and operating conditions [5–7]. FACTS devices regulate the power flow [8] and transmission voltage [9–11] through the rapid control action. Improvement in power system oscillation damping is one of the potential applications of the FACTS devices [12–19]. 1 This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (no. 2015R1A2A1A10052459).  Simple damping controls are prepared that specify some useful directions for obtaining the proposed control system parameters. Coordinated designs of PSS and FACTS device-based controllers have been investigated [20–23] to improve the damping characteristics of power system oscillations. A phase shifter can significantly reduce the generation cost [24]. It can also be used to solve the transient stability problem of power systems [25–26], to improve the power system dynamic performance [27] and to control the power flows [28–31]. In [32], the capability of a thyristor- controlled phase shifter (TCPS) in the damping of power system oscillations is investigated. In this paper, we propose the coordination of a TCPS- based damping controller and a PSS to ensure the power system stability through the rapid damping of power system oscillations. The proposed design is incorporated in the framework of the Phillips-Heffron model of a single- machine infinite-bus (SMIB) power system owing to its simplicity, and can be extended to multi-machine power systems. This study is conducted through a systematic approach of the following steps: 1. Mathematical modeling of the Phillips-Heffron model of an SMIB power system with the proposed design is established. 2. Detailed design methodologies are discussed and the parameters of the control system are achieved. 3. Performance of the proposed design is evaluated through a test power system. 4. Large system dynamics are taken into account under various system loadings. 5. Evaluation of the proposed design is investigated through eigenvalue analysis, time simulations, and damping torque contribution. 6. A comparative study is made on different control schemes, such as with an SMIB including a PSS and an SMIB including a TCPS-based damping controller. 7. Impact of the location for a TCPS is highlighted in the damping torque contribution. The main contributions of this paper are as follows:  The coordination of a TCPS-based damping controller and a PSS is proposed for attaining an improved power oscillations damping profile. 27 1582-7445 © 2017 AECE Digital Object Identifier 10.4316/AECE.2017.04004 [Downloaded from www.aece.ro on Friday, December 15, 2017 at 14:22:02 (UTC) by 115.145.148.65. Redistribution subject to AECE license or copyright.]