Improvement of damping characteristics and index evaluation of a wind-PV-thermal-bundled power transmission system by combining PSS and SSSC

ARCHIVES OF ELECTRICAL ENGINEERING VOL. 69(3), pp. 705–721 (2020) DOI 10.24425/aee.2020.133927 Improvement of damping characteristics and index evaluation of a wind-PV-thermal-bundled power transmission system by combining PSS and SSSC PING HEo , XINXIN WUo , CONGSHAN LIo , MINGMING ZHENGo , ZHAO LIo Zhengzhou University of Light Industry No.5, Dongfeng Road, Jinshui District, Zhengzhou City, Henan Province, China, 450002 e-mail: (Received: 16.12.2019, revised: 29.04.2020) Abstract: The grid integration of large-scale wind and solar energy affects the power flow of wind-PV-thermal-bundled power transmission systems and may introduce an unpredicted threat to the power system’s small signal stability. Meanwhile, a power system stabilizer (PSS) and static synchronous series compensator (SSSC) play an important role in improving the static and dynamic stability of the system. Based on this scenario and in view of the actual engineering requirements, the framework of wind-PV-thermal-bundled power transmitted by an AC/DC system with the PSS and SSSC is established considering the fluctuation of wind and photovoltaic power output and the characteristics of the PSS and SSSC. Afterwards, the situation model is constructed in the IEEE 2-area 4-unit system, and the influence of the PSS and SSSC on the system stability under different operating conditions is analyzed in detail through eigenvalue analysis and time-domain simulation. Finally, an index named the gain rate is defined to describe the improvement of the stability limitations of various wind-PV-thermal operating conditions with the PSS and SSSC. The results indicate (K) that the damping characteristics, dynamic stability and stability limitations for various wind-PV-thermal operating conditions of the wind-PV-thermal-bundled power transmission system can be significantly improved by the interaction of the PSS and SSSC. Key words: damping characteristics, eigenvalue analysis, power system stabilizer, windPV-thermal-bundled power system 1. Introduction With the advantages of mitigating energy crises and protecting the environment [1], windPV-thermal-bundled power transmitted by AC/DC systems is widely applied in the new energy 0 © 2020. The Author(s). This is an open-access article distributed under the terms of the Creative Commons AttributionNonCommercial-NoDerivatives License (CC BY-NC-ND 4.0, https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits use, distribution, and reproduction in any medium, provided that the Article is properly cited, the use is non-commercial, and no modifications or adaptations are made. 706 P. He, X. Wu, C. Li, M. Zheng, Z. Li Arch. Elect. Eng. delivery for large-scale energy bases in northwest, north, and northeast China. This can not only promote the comprehensive development and utilization of new energy bases and greatly alleviate the problem of electricity shortages in the central and eastern regions of China but also suppress peak shaving changes caused by fluctuations of wind and solar energy and improve the stability of long-distance power transmission and the utilization of DC equipment [2]. In this scenario, the large-scale integration of wind and solar energy, however, will also bring about adverse effects on power systems. Doubly fed induction generators (DFIGs) and photovoltaic power stations, associated with wind power and solar power, introduce interactions with synchronous generators (SGs), change the system’s power flow and affect the system’s damping characteristics, making the power system extremely vulnerable to low frequency oscillations when disturbed due to a decrease of damping [3, 4].The possibility of unbalanced power flow in power systems will markedly increase due to the random fluctuations of wind power [5–8] and photovoltaic power [9–12], introducing new challenges. Therefore, it is of great urgency to apply damping controllers to improve the damping characteristics of wind-PV-thermal-bundled power transmission systems. Some researchers have drawn much attention to this important topic. The damping of low frequency oscillations, particularly local area oscillations, can be dramatically improved due to the function of a power system stabilizer (PSS) [13–15]; hence, the small signal stability of the system is strengthened. The integration of wind power and photovoltaic power obviously widens the system eigenvalue range, which makes it fairly difficult to improve the small signal stability of inter-region oscillations only using the PSS [16, 17]. In addition, references [18–20] note that flexible AC transmission system (FACTS) devices can not only strengthen the system stability and reliability but also enhance the utilization efficiency of renewable resources by constantly controlling the power flow of transmission lines. The simulation curve of [21] indicates that a static synchronous series compensator (SSSC), as a series FACTS device, can reduce the system oscillation amplitude and accelerate the convergence process. Much work in references [22, 23] has proven that significant improvements in the damping characteristics, synchronous transmission power and transient stability limit can be achieved when using the SSSC. Specifically, as stated in [24], on the one hand, the PSS increases the damping of system oscillations; on the other hand, however, it leads to instability of the torsional mode. In addition, the PSS can be applied in a system with the SSSC with no detrimental influence on the torsional mode. In this paper, the effects of interactions between the PSS and SSSC on the damping characteristics and dynamic stability of a wind-PV-thermal-bundled power transmission system, including the wind-PV-thermal transmission distance, wind-PV-thermal grid-connect capacity and AC/DC transmission power ratio, are studied. Moreover, the gain rate index (K) is defined to measure the improvement of the stability limitations, which shows how and why the PSS and SSSC can affect the power system small signal stability under various wind-PV-thermal operating conditions. The contributions of the paper to the research field are as follows: – Establishing the framework of wind-PV-thermal-bundled power transmitted by an AC/DC system with the PSS and SSSC considering the fluctuation of wind and photovoltaic power output and the characteristics of the PSS and SSSC. – Constructing the situation model in the IEEE 2-area 4-unit system, and analyzing the influence of the PSS and SSSC on the system stability under different operating conditions in detail through eigenvalue analysis and time-domain simulation. Vol. 69 (2020) Improvement of damping characteristics and index evaluation 707 – Defining the gain rate index to measure the improvement of the stability limitations of various wind-PV-thermal operating conditions with the PSS and SSSC. The main structure of this paper is as follows. Section 1 introduces the research background and purpose of this paper. In Sect (...truncated)