Wind energy is a growing energy resource in the current energy transition. Massive new amounts are planned to be built in the face of the climate and energy crisis. The current state-of-the-art type-4 Wind Turbines (WT) uses a Fully Rated Converter (FRC) to decouple the rotor speed from the grid frequency. In recent years this type of WT has been involved in so-called sub-synchronous events. The Grid Side Converter (GSC) of the FRC is very similar to other Inverter Based Generation (IBG) such as: Photovoltaics (PV), Battery Energy Storage Systems (BESS) and HVDC-links. As this research is focused on the GSC, it is very relevant to the integration of other Renewable Energy Resources (RES) as well.
This thesis investigates Sub-Synchronous Control Interaction (SSCI), a relatively new phenomenon. The GSC interacts with the grid, which can cause a Sub-Synchronous Oscillation SSO, an oscillation below the system's fundamental frequency. This oscillation can lead to damage, increased components wear or triggering protection systems. After different facets of SSCI are discussed, a new solution is put forward in this thesis. By feeding wide area Phasor Measurement Unit (PMU)-based measurements into the control system of the WT, an algorithm is constructed to mitigate SSCI. This algorithm is tested on the ability to mitigate sub-synchronous event risks.

First, a WT model is selected in the DIgSILENT PowerFactory software to recreate sub-synchronous behaviour. This model is tested in the weak radial grid. The influence of the different control parameters on the sub-synchronous behaviour is investigated and comped to literature studies. Different tools are used for this research. PowerFactory is used for small signal analysis to obtain a linear dynamic model of the system. RMS-time simulations are used to test the oscillatory behaviour of the system. These results are further analysed using eigen-analysis on the linear model and Fourier and Prony analysis on the time simulations.
Then, the same WT-model is implemented in a modified IEEE-39 bus system to see the behaviour of SSO propagation in a transmission network. The results are compared to an analytical method to determine voltage oscillations based on mode shapes. However, as SSCI has a fundamentally different driving force, this method is not valid in this case. In the same transmission network, the influence of grid operations is tested. Different variations are tested: the connection point, power output of the WT, grid loading and disconnection of nearby connections. As all these features can vary during normal operation, it is vital to understand better which circumstances increase the risk of SSO event.

At last, using the knowledge obtained, a new control algorithm is proposed. This algorithm uses wide-area voltage angle measurements. These measurements can be provided by PMUs. A remote signal is fed into the control system. Minimal modifications are made to the control system for this. Additional damping is performed on the local voltage reference angle depending on the movement of the remote signal. This prevents the initialisation of SSCI. This implementation of a WAMC is tested using eigen-analysis and time simulations and shows promising results.

The results of this thesis research are also modelled in the NextGen GridOps Framework of DNV. The framework aims to stimulate a fast deployment of the finding of this thesis research in the field. This is accomplished by sharing knowledge in an accessible, structured environment. This allows taking the findings into consideration for solving the complex problems encountered by transmission and distribution system operators.

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.

With the advancements in technology and the enforcement of governmental regulations and incentives, the share of electric vehicles (EVs) in the mobility sector is on the rise. Although this aids the transition into a greener future with net-zero carbon emissions, the increase in EV penetration rates can have immense impacts on the grid and its operations. Coordinated charging strategies can help relieve grid stress by adhering to grid codes and requirements while carrying-out EV charging routines. Coordinated charging strategies can be of three types: centralized, decentralized, and price-oriented. The aim of this thesis is to investigate and mitigate the impacts of EV charging on Dutch residential grids, namely the impacts of voltage magnitude regulation and distribution transformer loading. This thesis proposes a decentralized coordinated charging strategy with local voltage control at its essence. The proposed charging strategy effectively allocates the charging power by prioritizing users based on their preferences, which are communicated to the charge controller through an IoT platform. Furthermore, in order to investigate whether users would be inclined to enroll into a coordinated charging routine, the impact on the user is also taken into account in this thesis by comparing to what extent can a user charge their EV battery with a coordinated charging strategy when compared with an uncoordinated one. Finally, all relevant and practical results from this thesis will be integrated into DNV's Next Generation Grid Operation Knowledge Framework to aid DNV employees in the future.