Oscillatory Stability of Power Systems with High Shares of Renewable Generation: Investigation of the Effectiveness of Wide-Area Selective Damping Control

Abstract

A large contribution to the total share of electricity generated in European power grid will come from renewable sources of energy in the near future due to European initiative to become carbon neutral. RES are connected to the grid with PE devices, which if not modelled correctly provide lower level of system stability and security of supply. The existing power grid with mainly synchronous generators will not be suited to operate in the future, when synchronous machines will become less important sources of energy. An increase in dynamic behaviour of the system could cause significant challenges for the existing system, which calls for new monitoring and control strategies. The aim of the project is twofold; firstly, to enhance system stability by deploying WAMS in power system with a massive share of RES to total electricity generation. Secondly, it focuses on developing and proposing a tool which will improve consultancy in future power grids. A tool developed is Next Generation Grid Operations (NextGen GridOps) Knowledge Framework which is conceptually designed by DNV. The effectiveness of WAMS applications on system stability improvements and damping enhancements will be evaluated by studying rotor angle stability as well as effect of WAMS on damping of electromechanical oscillations. The response to a disturbance of the remaining synchronous generators will be studied to evaluate the effect of different types of control schemes (grid-following, grid forming control) on the rotor angle stability. Rotor angle stability will be examined to show whether different control structures and WAMS will show enhancements of the overall stability through time domain simulations. WAMS structure in this project consists of PMUs as well as WADCs. While PMUs are sensors deployed in the system to provide synchrophasor measurement, WADCs are damping controllers deployed with an intent of enhancing damping in the system. This project build upon findings from Horizon 2020 MIGRATE Project. The effectiveness of grid-following control and grid-forming control on stabilizing the grid with massive penetration of PE devices are conducted to set the base case for evaluating the effect of WAMS. Modelling software used in the project is DIgSILENT PowerFactory 2021 SP1 and the PowerFactory Thesis Licence was provided by DIgSILENT GmbH for research and educational purposes. Based on the off-line numerical simulations conducted in IEEE 39 Bus New England test system it was found that WAMS functionality with corresponding PMUs and WADCs can decrease oscillations in the system. It has been verified that grid-following control enables 60% of RES penetration and grid-forming control enables penetration of RES above 80%. There have been two grid-forming controllers used in the system, where DVC is able to receive the stabilizing signal while VSM grid-forming controller has a supporting role. WAMS and corresponding WADCs deployed on DVCs are able to enhance damping of the low-frequency modes with frequencies below 2.0 Hz, which is supported by time domain simulations and by conducting Prony analysis. Eigenvalue analysis results for some cases with WAMS deployed show no additional enhancements, which is a consequence of newly introduced controllers and interactions among them and existing controllers. The practical implications of this Master's Thesis study have been modelled in the NextGen GridOps Framework with an intent to make a step towards real world implementation of the findings developed during the project. Framework modelling focused on implementing client maturity classification of WAMS deployments, contributing towards development of WAMS roadmaps and further deployment of WAMS solutions for grid operators as part of the DNV Next Generation Grid Operations advisory services. Work done and information implemented will be valuable for DNV while solving the complex process of future grid operations and at the same time bringing newly developed knowledge into practice. The framework development part of the project ties in with scientific contribution by allowing newly developed information to be further explored. Effectiveness of WAMS and WADCs on improving selective damping and consequently enhancing system stability has been identified in this project through use of DVCs. It has been proven that VSM control has a better stabilizing effect and would allow even further enhancement of damping critical oscillation modes. Higher damping in the system increases the stability and consequently higher security of energy supply.