Tuning of Cascaded Controllers for Robust Grid-Forming Voltage Source Converter

International audienceFrom the origin of the grid, energy has been delivered to electrical loads mainly by synchronous machines. All the main rules to manage the grid have been based on the electromechanical behavior of these machines which have been extensively studied for many years. Due to the increase of HVDC link and renewable energy sources as wind turbine and PV, power converters are massively introduced in the grid with a fundamentally different dynamic behavior. Some years ago, they were connected as simple power injector. Then, they were asked to provide some ancillary services to the grid, in the future, grid forming capability will be required. Even if gridforming converters had been extensively studied for microgrids and offshore grids, it has to be adapted to transmission grid where the topology may be largely modified. This paper presents an algorithm for calculating the controller parameters of a gridforming converter which guarantee a stable behavior for many different configurations of the grid

Case Study of Non-Isolated MMC DC-DC Converter in HVDC Grids

Peer reviewedPublisher PD

Modular modelling of combined AC and DC systems in dynamic simulations

A formulation is proposed in which an AC-DC system is modeled as a combination of AC grids, DC grids, injectors, AC two-ports and AC/DC converters, respectively. This modular modelling facilitates the dynamic simulation of future complex AC/DC systems. Furthermore, it can be exploited by the solver, which performs less operations on components with lower dynamic activity, and offers parallel processing of the time simulation. This approach is illustrated on a test system in which a multi-terminal DC grid connects two asynchronous AC systems, allows frequency support between them, and acts as emergency control against AC voltage instability

Effect of Using PLL-Based Grid-Forming Control on Active Power Dynamics Under Various SCR

This paper investigates the effect of using phaselocked loop (PLL) on the performance of a grid-forming controlled converter. Usually, a grid-forming controlled converter operates without dedicated PLL. It is shown that in this case, the active power dominant dynamics are highly dependent to the grid short circuit ratio (SCR). In case of using PLL, the obtained results illustrate that the SCR has a negligible effect on the dynamic behavior of the system. Moreover, the power converter will not participate to the frequency regulation anymore; therefore, the converter response time can be adjusted independently to the choice of the droop control gain, which is not possible without PLL. A simple equivalent model is presented which gives a physical explanation of these features

Assessment of interoperability in multi-vendor VSC-HVDC systems : interim results of the Best Paths DEMO #2

This paper describes the methodology and interim results from the ongoing European project Best Paths DEMO #2, which is the first attempt to undertake systematic investigation on interoperability in multi-vendor VSC-HVDC systems. The study is based on state-of-the-art technologies provided by three world-class HVDC vendors and involves TSOs and academics for investigations covering various HVDC layouts, from point-to-point to radial and meshed multi-terminal structures. The paper describes the methodology used to assess and maximize interoperability, which comprises two stages: the first one relies on electromagnetic transient (EMT) simulation tools, while the second and ongoing one relies on real-time simulation with actual control cubicles provided by HVDC vendors. The paper mainly reports on the different tasks which were carried out during the first stage (EMT simulations) and exhibits the results observed. The main tasks and results are listed as follows: - Commonly agreed definition of interoperability - Definition of common converter specifications for all involved HVDC vendors, based on the ENTSO-E Network Code for realism and replicability - Definition of 5 different DC systems (including DC grids) on which interoperability should be assessed - Provision of detailed vendor-specific EMT converter models, and their individual validation - Assessment of interoperability on more than 1.000 realistic scenarios, from which 15% are representative of actual interoperability issues between the vendors - First set of recommendations to maximize interoperability Finally, the paper provides insights on the second and ongoing stage of the project based on real-time simulation using actual vendor control cubicles for deeper investigations

Protection of single-phase fault at the transformer valve-side of FB-MMC based bipolar HVDC systems

Although the probability of occurrence of ac grounding faults at the valve side of the interface transformer of a high-voltage dc (HVdc) link is low, they may cause high risks to the converter when compared to grid-side ac faults. This article analyzes the characteristics of valve-side ac single-phase-to-ground faults in full-bridge modular multilevel converters (FB-MMCs)-based bipolar HVdc systems. Overcurrents in the converter arms are analyzed and it is shown that overvoltages in FB submodules occur without an appropriate protection in place. Two strategies are investigated to protect the FB-MMC during the fault and corresponding controllers are designed. The effectiveness of the presented strategies for the prevention of overcurrents and overvoltages, upon nonpermanent and permanent faults, and system postfault restoration is investigated. For completeness, the strategies are also verified by conducting simulations in PSCAD/EMTDC

Contrôle du Convertisseur Modulaire Multiniveaux connecté à une source DC inductive

L'utilisation de la transmission DC est particulièrement avantageuse pour la transmission à longue distance et l'interconnexion des réseaux AC asynchrones. Plusieurs topologies de convertisseur peuvent être utilisées pour le HVDC. Les convertisseurs modulaires multiniveaux (MMC) sont les plus favorisés étant donné leurs avantages technologiques par rapport aux autres topologies de convertisseurs. Du fait de leur maturité industrielle, ils se sont imposés maintenant pour tous les convertisseurs AC/DC à transistors de forte puissance. Jusqu'ici, ils ont toujours été étudiés avec une source de tension côté DC. Or, lorsqu'ils sont équipés de DC breaker, on associe une inductance en série pour limiter les variations de courant. Ceci a des conséquences en terme de modélisation puis de détermination de la commande. Cet article a pour objectif de proposer une modification de commande afin de prendre en compte cette inductance

Coupling Influence on the dq Impedance Stability Analysis for the Three-Phase Grid-Connected Inverter

The dq impedance stability analysis for a grid-connected current-control inverter is based on the impedance ratio matrix. However, the coupled matrix brings difficulties in deriving its eigenvalues for the analysis based on the general Nyquist criterion. If the couplings are ignored for simplification, unacceptable errors will be present in the analysis. In this paper, the influence of the couplings on the dq impedance stability analysis is studied. To take the couplings into account simply, the determinant-based impedance stability analysis is used. The mechanism between the determinant of the impedance-ratio matrix and the inverter stability is unveiled. Compared to the eigenvalues-based analysis, only one determinant rather than two eigenvalue s-function is required for the stability analysis. One Nyquist plot or pole map can be applied to the determinant to check the right-half-plane poles. The accuracy of the determinant-based stability analysis is also checked by comparing with the state-space stability analysis method. For the stability analysis, the coupling influence on the current control, the phase-locked loop, and the grid impedance are studied. The errors can be 10% in the stability analysis if the couplings are ignored.This research was funded by MIGRATE project under European Union’s Horizon 2020 research and innovation program, grant number 691800

Bmcc1s, a Novel Brain-Isoform of Bmcc1, Affects Cell Morphology by Regulating MAP6/STOP Functions

The BCH (BNIP2 and Cdc42GAP Homology) domain-containing protein Bmcc1/Prune2 is highly enriched in the brain and is involved in the regulation of cytoskeleton dynamics and cell survival. However, the molecular mechanisms accounting for these functions are poorly defined. Here, we have identified Bmcc1s, a novel isoform of Bmcc1 predominantly expressed in the mouse brain. In primary cultures of astrocytes and neurons, Bmcc1s localized on intermediate filaments and microtubules and interacted directly with MAP6/STOP, a microtubule-binding protein responsible for microtubule cold stability. Bmcc1s overexpression inhibited MAP6-induced microtubule cold stability by displacing MAP6 away from microtubules. It also resulted in the formation of membrane protrusions for which MAP6 was a necessary cofactor of Bmcc1s. This study identifies Bmcc1s as a new MAP6 interacting protein able to modulate MAP6-induced microtubule cold stability. Moreover, it illustrates a novel mechanism by which Bmcc1 regulates cell morphology

Applications of Real-Time Simulation Technologies in Power and Energy Systems

Real-time (RT) simulation is a highly reliable simulation method that is mostly based on electromagnetic transient simulation of complex systems comprising many domains. It is increasingly used in power and energy systems for both academic research and industrial applications. Due to the evolution of the computing power of RT simulators in recent years, new classes of applications and expanded fields of practice could now be addressed with RT simulation. This increase in computation power implies that models can be built more accurately and the whole simulation system gets closer to reality. This Task Force paper summarizes various applications of digital RT simulation technologies in the design, analysis, and testing of power and energy systems