Shadi Khaleghi Kerahroudi

Initial development of a novel stability control system for the future GB transmission system operation

With the increasingly fast large-scale deployment of renewable energy sources in the UK more state-of-the-art transmission system technologies such as Thyristor Controlled Series Compensation (TCSC) and embedded High Voltage DC (HVDC) links will come into operation in the future GB transmission system. These power flow control devices can be utilized in a co-coordinated manner for better stability control due to their capability to rapidly control the transmitted power. However, an operational stability control system is required to ensure the coordinated control of power flow control devices in order to achieve optimal dynamic performance and make the stability limits a less binding factor than the thermal limit under all operating conditions. This paper describes the method and aspects related to interfacing PowerFactory DIgSILENT and Matlab program as an initial step of developing stability control system for the GB transmission. Sampled regulator design method is implemented for design of controller using Matlab program. This method is very attractive for applications in large integrated power systems since the controller design only requires the knowledge of a nonparametric model of power system i.e. the open-loop step response, which is easily obtainable compared to development of a parametric model of the power system.

System stability improvement through HVDC supplementary Model Predictive Control

Bulk power transfer requirements over long distances within a country or between neighboring countries as well as rapid increase in the number of offshore wind farms, have increased the application of high voltage DC links. Apart from the controllable power flow function of HVDC systems, advanced controllers can be employed to extend their functionality for dynamic and transient stability improvement of AC systems. As an attempt to improve the influence of HVDC technology on AC system stability, this paper proposes a supplementary active power controller for the HVDC system. The Model Predictive Control (MPC) approach is considered for the control design. The design process of weight tuning and parameterization of the MPC controller has been investigated. Additionally the effect of controller model reduction is demonstrated in the presented results.

Investigating the impact of stability constraints on the future GB transmission system

High penetration of wind power is anticipated in order to increase the share of renewable energy sources up to 20% in 2020. Therefore, in the future there will be major changes to the GB generation profile, both in terms of equipment type and geographical location, which will result in the need to transfer large amounts of renewable energy from the north of Scotland to the mainland demand centers in the GB south. Due to the fact that the existing network has insufficient transmission capacity to accommodate the increasing power transfer, the GB system operator and owners are required to introduce new reinforcements as well as maximizing the use of existing transmission lines to avoid constraining some generators and also at the same time improve the stability limits. In this paper the capability of several new transmission technologies such as Thyristor Controlled Series Capacitor (TCSC) and embedded High Voltage DC (HVDC) links are investigated with regard to increasing power transfer limits and their effect on dynamic stability control is also investigated. Initially, this study proposes a hierarchical Control Strategies for co-ordinated control of the TCSC and HVDC links for all operational point. Finally, the main objective of the study is to analyse and develop an operational stability control system (SCS) that will be able to provide fully co-ordinated control of TCSC and HVDC links in order to achieve best dynamic performance and make the stability limits less binding factor than the thermal limit under all operating conditions using a stabilising feedback control system. This implies that the intertrip actions will be reduced as well as maintaining and enhancing the stability for every dispatched operating point.

Application and Requirement of DIgSILENT PowerFactory to MATLAB/Simulink Interface

Simulation tools are the most economical solution for modelling and design of various components of large-scale power systems. However, as the complexity in the integrated electric power network grows, the need for more comprehensive simulation tools rises. Modern simulation tools have therefore been developed in line with this ever increasing need by means of integration of improved user interfaces. Interfacing of the simulation tool to an external program/mathematical tool extends the capability of the simulation tool in a more effective execution of the simulation, particularly in an area where the external program/algorithm provides more advanced technique and flexibility, e.g. the advanced control system design in MATLAB control toolbox. This chapter describes the process of interfacing DIgSILENT PowerFactory to MATLAB/Simulink program. Two study cases will be presented in this chapter. These study cases are set up and provided to allow the readers to understand the process and steps of linking DIgSILENT PowerFactory to the MATLAB/Simulink program.

Evaluating the Novel Application of a Class of Sampled Regulators for Power System Control

The focus of this paper is on the nonparametric system design approach using a class of sampled regulators. Based on the review and evaluation of two stability design methods that were originally established for this class of sampled integral regulators, this paper has extended the stability theory and design algorithms in order to additionally consider generalized proportional-integral-derivative regulators. The link between the two original design methods has been revealed, based on which the whole benefit of the class of sampled regulator design methods can be embraced in a single framework. Furthermore, the suitability of the proposed design algorithms has been demonstrated in several power system applications.

Modelling of reduced GB transmission system in PSCAD/EMTDC

Energy and environmental issues are two of the greatest challenges facing the world today. In response to energy needs and environmental concerns, renewable energy technologies are now considered the future technologies of choice. Renewable energy is produced from natural sources that are clean and free; however, it is widely accepted that renewable energy is not a solution without challenges. An example of this can be seen in the UK, where there is much interest amongst generation developers in the construction of new large scale onshore and offshore wind farms, especially in Scotland. The stability of electric power systems is also an important issue. It is important to have full knowledge of the system and to be able to predict the behaviour under different situations is an important objective. As a result, several industrial grade power system simulator tools have been developed in order to estimate the behaviour of the electric power system under certain conditions. This paper presents a reduced Great Britain (GB) system model for stability analysis using PSCAD/EMTDC. The reduced model is based upon a future GB transmission system model and, hence, contains different types and mix of generation, HVDC transmission lines and additional interconnection. The model is based on the reduced DIgSILENT PowerFactory model developed by National Grid.

Power system stability enhancement of the future GB transmission system using HVDC link

As a consequence of the fast development of renewable energy sources in the UK, higher transmission capacity will be required to integrate potentially large volumes of wind generation in the future. Also, over the next decade, maintaining the transmission system security and stability will become more difficult. A major increase in the application of HVDC transmission technology and the deployment of series compensation within the existing AC transmission system is expected to provide the required transfer capability in the future. However, there is also a need to employ smarter ways of operating these power flow control devices. Firstly, this paper investigates the capability of the HVDC link in improving the inter-area power oscillation damping. Two approaches in the design of power oscillation damping controller are demonstrated. Secondly, the paper presents the application of the HVDC links set-point adoption for the stability enhancement through a novel non-parametric control system design approach using the sample regulator control design method. This method is mainly attractive for applications in large integrated power systems since the controller design only requires knowledge of the nonparametric model of the power system i.e. the open-loop step response, which is easily obtainable compared to development of parametric model of the power system.

A critical evaluation of the application of HVDC supplementary control for system stability improvement

Bulk power transfer requirements over long distances within a country or between neighboring countries as well as rapid increase in the number of offshore wind farms, have increased the application of high voltage DC links. Apart from the controllable power flow function of HVDC systems, advanced controllers can be employed to extend their functionality for dynamic and transient stability improvement of the underlying AC systems. This paper compares and critically evaluates HVDC supplementary controller strategies for improving AC system stability. A Preliminary explanation of the controller design process for each controller type as well as a brief comparison on their application to damp the inter-area oscillations have been presented in this paper.

Application of a novel stability control system for coordination of power flow control devices in the future GB transmission system

With increasing large-scale renewable energy sources in the UK and the need for adequate transmission capacity to accommodate the upcoming renewable generations, more state-of-the-art power flow control devices such as embedded High Voltage DC (HVDC) links will soon be commissioned in the GB HV transmission system to provide the additional capacity. An operational stability control system is required to ensure the coordinated control of power flow control devices in order to achieve better dynamic performance and stability. The focus of this paper is to demonstrate the capability of a multi-variable controller for the coordinated control using a non-parametric sampled regulator control design method. This method is practical for applications in large power systems since the complexity of the controller design does not increase with the size and dynamic of the power system. Also, this design method is demonstrated in two power system applications in this paper.

Transmission system stability enhancement using demand management technology

The penetration of wind energy in power system is growing dramatically world wide. Consequently, there are some new challenges appeared on power system. Smart demand technology involves new communication technologies to make sure actions can be fast enough to prevent instability situation of generators. Due to the high level of renewable energy in power system, flexible demand becomes a future option for wind intermittency situation. Intertrip is one of the automatic actions that can help release overload and stability situation. It is normally used for generations to be disconnected followed by a trip of circuit. It can also be used for demand side intertrip. This paper will show how demand disconnection and intertripping technology can improve power system stability. Power Transfer Distribution Factor (PTDF) will be used to define wind transfer corridor circuits. After the corridor is located, the sensitivity of individual demand will be calculated by using PTDF method. This sensitivity factor will be used to select demand intertrip accordingly. It is defined as smart intertrip controller in the paper. A reduced UK model will be used in the paper to prove how demand side intertrip technology can improve system stability during high wind scenario.