Stijn Cole

Generalized Steady-State VSC MTDC Model for Sequential AC/DC Power Flow Algorithms

In this paper, a steady-state multi-terminal voltage source converter high voltage direct current (VSC MTDC) model is introduced. The proposed approach is extended to include multiple AC and DC grids with arbitrary topologies. The DC grids can thereby interconnect arbitrary buses in one or more non-synchronized AC systems. The converter equations are derived in their most general format and correctly define all set-points with respect to the system bus instead of the converter or filter bus, which is often done to simplify calculations. The paper introduces a mathematical model to include the converter limits and discusses how the equations change when a transformerless operation is considered or when the converter filter is omitted. An AC/VSC MTDC power flow is implemented using MATPOWER to show the validity of the generalized power flow model.

Modeling of Multi-Terminal VSC HVDC Systems With Distributed DC Voltage Control

This paper discusses the extension of electromechanical stability models of voltage source converter high voltage direct current (VSC HVDC) to multi-terminal (MTDC) systems. The paper introduces a control model with a cascaded DC voltage control at every converter that allows a two-terminal VSC HVDC system to cope with converter outages. When extended to an MTDC system, the model naturally evolves into a master-slave set-up with converters taking over the DC voltage control in case the DC voltage controlling converter fails. It is shown that the model can be used to include a voltage droop control to share the power imbalance after a contingency in the DC system amongst the converters in the system. Finally, the paper discusses two possible model reductions, in line with the assumptions made in transient stability modeling. The control algorithms and VSC HVDC systems have been implemented using both MatDyn, an open source MATLAB transient stability program, as well as the commercial power system simulation package EUROSTAG.

Implementation of a Massively Parallel Dynamic Security Assessment Platform for Large-Scale Grids

This paper presents a computational platform for dynamic security assessment (DSA) of large electricity grids, developed as part of the iTesla project. It leverages high performance computing to analyze large power systems, with many scenarios and possible contingencies, thus paving the way for pan-European operational stability analysis. The results of the DSA are summarized by decision trees of 11 stability indicators. The platform’s workflow and parallel implementation architecture is described in detail, including the way commercial tools are integrated into a plug-in architecture. A case study of the French grid is presented, with over 8000 scenarios and 1980 contingencies. Performance data of the case study (using 10 000 parallel cores) is analyzed, including task timings and data flows. Finally, the generated decision trees are compared with test data to quantify the functional performance of the DSA platform.

Robust Modeling Against Model-Solver Interactions for High-Fidelity Simulation of VSC HVDC Systems in EUROSTAG

Phasor based power system simulation software was originally conceived to study electromechanical interactions between rotating machinery and the network. Today, fast power electronic equipment is also commonly represented in phasor based power system software, although their dynamic behavior may violate some assumptions that lie at the basis of the phasor approximation. Modeling fast acting devices in phasor based power system software presents a number of challenges: due to the small time constants involved, time efficient simulation is a challenge. Furthermore, adverse interactions can occur between detailed models and state-of-the-art solution methods. The paper presents a robust implementation method on three levels: robustness of the tool, of the interface, and of the model itself, that leads to robust, accurate and efficient simulation of power systems with fast acting devices.

Cost-benefit analysis of a coordinated grid development in the North Sea

A full Cost-Benefit Analysis (CBA) of a meshed offshore grid in the Northern Seas with respect to radial configurations has been performed. In this CBA, three scenarios have been analysed: the ENTSO-E Vision 4 scenario with 111 GW of offshore wind, the PRIMES reference scenario with 70 GW of offshore wind, and the NSCOGI scenario with 55 GW of offshore wind. The offshore grid infrastructure cost is calculated, and the benefits are assessed. The CBA is based on the ENTSO-E Draft CBA methodology. The costs were calculated using Ecofys offshore transmission cost modelling tool and Tractebel Engineerings techno-economical tool SCANNER? is used for the calculation of the benefits.

Long-term planning of electricity distribution systems integrating flexibility options

This paper presents the application of a long-term distribution system planning tool, Smart Sizing to a Belgian distribution system. The tool takes into account smart technologies such as load flexibility during the planning stage. In addition to the traditional decision variables in planning like the number of substations, transformers, feeder size etc. the Smart Sizing tool includes the type of flexibility, the flexibility profile etc. as the decision variables. A set of cases are analysed to show some of the features of the tool. In case 1, no smart technologies are used. In case 2, the tool can decide to contract load flexibility to reduce the investment in electrical equipment. In case 3, load shedding can be activated.

Planning criteria benchmarking and voltage stability study for Marafiq's Yanbu network

Due to increasing power requirements of the growing industrial sectors, the Power and Water Utility Company for Jubail and Yanbu (Marafiq) foresees a significant load increase in its network, which consequently might impact the voltage stability. Prior to the reinforcement of the system with additional means of reactive power compensation, an international benchmarking covering Saudi Arabia and other systems presenting similar characteristics was undertaken to update the voltage planning criteria, including the definition of the incidents that the system must withstand without activating defence schemes and/or provoking a supply interruption. Particular attention was brought to the way important share of rotating load is considered in the criteria. Then, the Voltage Stability study was performed, considering the criteria retained, to assess the reinforcements needed in Marafiq Yanbus Power System to reach the desired level of robustness. In the end, the added value of these reinforcements was discussed and their costs compared.

Automatic tuning of out-of-step relays

A method and prototype tool for tuning out-of-step relay parameters is presented. A decision making matrix is built from dynamic simulation results. Based on this matrix, an optimization problem is formulated that determines the out-of-step relay parameters that minimize the number of cases in which the relays do not operate satisfactorily. The method has been successfully tested on a simple test case with one relay to tune, and on a four zone test case where several relays are tuned for different operating scenarios.