Impedance-Based Modelling of Hybrid AC/DC Grids With Synchronous Generator for Interaction Study and Dynamic Improvement

Hybrid AC/DC grids are increasingly been seen as the most important network structure for future transmission infrastructures. An emerging challenge to such grids is the constant interaction between various components in the system. Interactions could occur in many intricate forms including between and within the AC and DC subnetworks. However, considering the complexities involved, methods for detection that are intuitive, compact, and relatively straightforward to apply are lacking. In this paper, device-level closed-loop impedance models of subsystems in a hybrid AC/DC grid are extended compactly to subnetwork equivalents in the form of matrices. Then, interaction analysis between a voltage source converter (VSC) interconnected on both sides, and a synchronous generator with excitation control is carried out as a case study to highlight potentially detrimental interactions. The analysis is carried out in the frequency domain and validated with a nonlinear time domain simulations in MATLAB/SIMULINK.Peer ReviewedPostprint (author's final draft

Impedance Modelling and Parametric Sensitivity of a VSC-HVDC System: New Insights on Resonances and Interactions

Pervasiveness of power converters in the electric power system is expected in the future. Such large penetration will change the current power system dynamics leading to uncertain, unexpected, and potentially critical responses. This paper investigates the stability and resonance of a VSC-HVDC (Voltage Source Converter High Voltage Direct Current) link within an AC grid, whilst providing insights into resonances having a role on the grid. This is studied through the impedance-based modelling of the entire system (AC and DC grids), including controls of converters. Additionally, the impact of the different parameters of the hybrid AC-DC power system such as control systems and grid components on the system dynamics and stability is investigated. From this study, the impact of the system components and the controls of the converter on overall resonance response and stability is shown, including potential undesired sub-synchronous and harmonic resonances due to AC-DC system interactions. The analytical impedance-based models developed and obtained is validated through time-domain simulations, the physical model of the whole system is built in Simscape™ Power Systems™ and control systems in MATLAB/Simulink® (R2017b). This has demonstrated the validity of the model to deal with and detect such dynamics

Lightning Effects on LED-Based Luminaires

This chapter gives an extensive overview into the nature of the environment that luminaires and thus LEDs are subjected to during the event of a lightning stroke. Direct lightning stroke almost always results in instant damage for low-voltage connected devices, except in “extraordinary circumstances” where random components may survive. This is usually not a subject for debate and is not the subject of this monograph. Indirect consequences of lightning strokes, however, can be effectively mitigated as described. This chapter also delves into a realistic expected overvoltage levels for two typical systems, overhead lines and insulated cables, as obtained from lightning studies on a power network supplying power to LED devices and thus justifies the recommendations by several standards. In addition, it shows the importance of an often neglected device—MOV in mitigating attendant surges due to lightning to a level that can be withstood by LEDs and associated devices.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material

Robust decentralized approach to interaction mitigation in VSC-HVDC grids through impedance minimization

An interconnection of independently designed voltage source converters (VSCs) and their control in high voltage DC grids can result in network-level detrimental interactions and even instability. In many cases, vendors are not willing to share proprietary information about their designs in a manner that allows the entire system to be designed considering the collective dynamics. Besides, such an endeavour is not realistic. In this paper, robust network-level global controllers are proposed to decouple interacting VSCs through an impedance shaping technique. Particularly, the global controllers are designed without any need to establish the internal controller structure of any VSC which is often proprietary. Rather, the global controllers rely on the externally measurable feedback impedance of each VSC in stand-alone and the rest of the system. It is demonstrated how robust convex optimization framework can be exploited to robustly shape global feedback impedances to obtain a decoupled network. The synthesized controllers are validated through nonlinear simulations of the physical modelPostprint (author's final draft

Interconnection of hybrid AC/DC grids of arbitrary strengths using supplementary bus-voltage feedforwards

This article proposes an intuitive methodology to analyse and mitigate system-level interactions in hybrid ac/dc networks interconnecting ac grids of arbitrary strengths, and especially weak grids. In particular, the challenge of interconnecting such grids is posed as an interaction problem in which the mechanism can be analysed explicitly through the unique ac/dc interaction functions. Then, it is demonstrated how these interaction functions can be manipulated to mitigate ac–ac, ac–dc, and dc–dc interactions simultaneously through a simple augmentation of the classic vector current control structure. The augmented loop adopts supplementary bus-voltage feedforwards from the ac and dc-sides. Significant improvements over the classic structure are demonstrated for an high voltage dc-link connecting two ac grids with arbitrary grid strengths particularly a very weak ac connection. It is shown how these supplementary loops provide a more inclusive and flexible solution to contradictory requirements on existing control, with a thorough system outlook. In addition, it is shown that the augmented loop is also beneficial for system dynamics when the grid is strong than without it. The analysis is carried out in the frequency domain, and performance is validated with nonlinear time-domain simulations.Postprint (author's final draft

Lightning Effects on LED-Based Luminaires

This chapter gives an extensive overview into the nature of the environment that luminaires and thus LEDs are subjected to during the event of a lightning stroke. Direct lightning stroke almost always results in instant damage for low-voltage connected devices, except in “extraordinary circumstances” where random components may survive. This is usually not a subject for debate and is not the subject of this monograph. Indirect consequences of lightning strokes, however, can be effectively mitigated as described. This chapter also delves into a realistic expected overvoltage levels for two typical systems, overhead lines and insulated cables, as obtained from lightning studies on a power network supplying power to LED devices and thus justifies the recommendations by several standards. In addition, it shows the importance of an often neglected device—MOV in mitigating attendant surges due to lightning to a level that can be withstood by LEDs and associated devices