Generalized Voltage-based State-Space Modelling of Modular Multilevel Converters with Constant Equilibrium in Steady-State

This paper demonstrates that the sum and difference of the upper and lower arm voltages are suitable variables for deriving a generalized state-space model of an MMC which settles at a constant equilibrium in steady-state operation, while including the internal voltage and current dynamics. The presented modelling approach allows for separating the multiple frequency components appearing within the MMC as a first step of the model derivation, to avoid variables containing multiple frequency components in steady-state. On this basis, it is shown that Park transformations at three different frequencies ($+\omega$, $-2\omega$ and $+3\omega$) can be applied for deriving a model formulation where all state-variables will settle at constant values in steady-state, corresponding to an equilibrium point of the model. The resulting model is accurately capturing the internal current and voltage dynamics of a three-phase MMC, independently from how the control system is implemented. The main advantage of this model formulation is that it can be linearised, allowing for eigenvalue-based analysis of the MMC dynamics. Furthermore, the model can be utilized for control system design by multi-variable methods requiring any stable equilibrium to be defined by a fixed operating point. Time-domain simulations in comparison to an established average model of the MMC, as well as results from a detailed simulation model of an MMC with 400 sub-modules per arm, are presented as verification of the validity and accuracy of the developed model

Synthesis of different types of energy based controller for a Modular Multilevel Converter integrated in a HVDC link

Modular Multilevel Converters are becoming increasingly popular with the development of HVDC connection and, in the future, Multi Terminal DC grid. A lot of publications have been published about this topology these last years since it was first proposed. Few of them are addressing explicitly the 2 different roles that are held by this converter in a HVDC link: controlling the power or controlling the DC voltage level. Moreover, for a given function, different ways of controlling this converter may be considered. This paper proposes an overview of the different solutions for controlling the MMC and proposes a methodology to synthesize the control architecture

Teaching drive control using Energetic Macroscopic Representation - expert level

International audienceThe Energetic Macroscopic Representation (EMR) has been developed in 2000 to develop control of electric drives. Since 2002 this graphical tool has been introduced to teach drive control in France, then Canada, Switzerland and China. The University of Lille proposes two drive control units using EMR for students in electrical engineering: initiation level and expert level. A first paper has described the initiation level with the simulation of an electric vehicle. This second paper deals with the content of the expert level unit and describes the simulation project of a wind energy conversion system using a MPPT (Maximal Power Point Tracking) strategy

Teaching drive control using Energetic Macroscopic Representation - expert level

International audienceThe Energetic Macroscopic Representation (EMR) has been developed in 2000 to develop control of electric drives. Since 2002 this graphical tool has been introduced to teach drive control in France, then Canada, Switzerland and China. The University of Lille proposes two drive control units using EMR for students in electrical engineering: initiation level and expert level. A first paper has described the initiation level with the simulation of an electric vehicle. This second paper deals with the content of the expert level unit and describes the simulation project of a wind energy conversion system using a MPPT (Maximal Power Point Tracking) strategy

Les réseaux HVDC multi-terminaux : des défis multiples en génie électrique

National audienceLes systèmes électriques à très haute tension ont besoin d'être renforcés pour faciliter les échanges, maintenir la sécurité de fonctionnement, et raccorder des sources offshore. Certaines limites des réseaux alternatifs apparaissent alors. Les réseaux à courant continu haute tension (HVDC) multiterminaux peuvent être une alternative sous réserve de trouver des solutions aux barrières scientifiques et technologiquesexistantes. Les défis rencontrés sont au coeur du génie électrique, tant au niveau du matériau, du composant que du système. Cetarticle présente les principaux challenges à relever dans le domaine du génie électrique pour rendre possible l'exploitationfiable et sûre des réseaux HVDC.</p

Evaluation de la Performance des Réglages de Fréquence des Eoliennes à l'Echelle du Système Electrique (Application à un Cas Insulaire)

L intégration croissante de la production éolienne ne participant pas au réglage de fréquence induit de nouvelles difficultés de gestion des systèmes électriques. Ces problèmes sont d autant plus significatifs que le réseau est faible. La présente thèse vise à évaluer la performance et la fiabilité du réglage de fréquence des éoliennes à l échelle du système électrique. Les études sont appliquées sur un réseau insulaire.D abord, l impact d un fort taux de pénétration de la production éolienne sur l allocation de la réserve primaire et sur le comportement dynamique du réseau est caractérisé. Il est montré que la participation des éoliennes au réglage de fréquence est techniquement indispensable pour le maintien de la sûreté du système électrique à partir d un certain taux de pénétration. Deux solutions permettant aux éoliennes de contribuer au réglage de fréquence sont ensuite étudiées par simulations dynamiques. La performance d une inertie émulée est caractérisée en considérant l impact du point de fonctionnement initial des éoliennes et des paramètres du contrôleur. La contribution de la réserve éolienne à l amélioration de la performance dynamique du système est également identifiée.Afin d évaluer le potentiel et la fiabilité de la réserve éolienne, la dernière partie de ce travail est consacrée aux études statistiques prenant en compte la variabilité et l incertitude de la prévision de la production. Deux stratégies du placement de réserve sont proposées et comparées. L impact des erreurs de prévision sur le potentiel de réserve éolienne est également mis en évidence. Enfin l énergie réglante d une ferme et la plage de réglage du statisme éolien sont caractériséesThe increasing development of wind power that does not participate in frequency control leads to new challenges in the management of electrical power systems. The problems are more significant in weak power grids. The present thesis aims to evaluate the performance and the reliability of frequency response from wind turbines on a system-wide scale. Studies are applied onto an isolated power grid.First of all, the impact of high levels of wind penetration on primary reserve allocation and on grid dynamic behaviour is characterized. It is shown that the participation of wind turbines in frequency regulation is technically required for maintaining power system security from a certain wind penetration rate.Two solutions allowing wind turbines to contribute to frequency control are then studied through dynamic simulations. The performance of emulated inertia is characterized by taking into account the impact of initial wind operating point and controller parameters. The contribution of wind power reserve to system dynamic performance improvement is also identified.In order to assess the potential and the reliability of wind primary reserve, the last part of this research work is devoted to statistical analyses considering the variability and the prediction uncertainty of wind generation. Two strategies for reserve allocation are proposed and compared. The impact of forecast errors on the potential of wind power reserve is also highlighted. Finally the power frequency characteristic of a wind farm as well as the droop adjustment range is characterizedVILLENEUVE D'ASCQ-ECLI (590092307) / SudocSudocFranceF

Critical clearing time determination and enhancement of grid-forming converters embedding virtual impedance as current limitation algorithm

International audienceThe present paper deals with the post-fault synchronization of a voltage source converter based on the droop control. In case of large disturbances on the grid, the current is limited via current limitation algorithms such as the virtual impedance. During the fault, the power converter internal frequency deviates resulting in a converter angle divergence. Thereby, the system may lose the synchronism after fault clearing and which may lead to instability. Hence, this paper proposes a theoretical approach to explain the dynamic behavior of the grid forming converter subject to a three phase bolted fault. A literal expression of the critical clearing time is defined. Due to the precise analysis of the phenomenon, a simple algorithm can be derived to enhance the transient stability. It is based on adaptive gain included in the droop control. These objectives have been achieved with no external information and without switching from one control to the other. To prove the effectiveness of the developed control, experimental test cases have been performed in different faulted conditions

DQ impedance stability analysis for the power-controlled grid-connected inverter

For a grid-connected inverter requiring the ac volt- age magnitude and the active power control, both vector control and power synchronization control can be applied. The stability comparison based on the dq impedance stability analysis between both control are carried out via three factors including the grid impedance, the inner current loop and the virtual impedance. The dq impedances of the inverter based on both control are derived. The determinant of the impedance ratio is used for the stability analysis. The bode plot of the grid impedance and the inverter impedance are present to assist the stability analysis and explain their interactions. It is found that increasing the grid impedance and the cut-off frequency of the current loop stabilize the inverter with the power synchronization control, which is converse to the vector control. Furthermore, the inverter with the power synchronization control may suffer the instabilities when connecting to a strong grid. The virtual inductor and resistor are proposed to enhance the stability for the vector control and the power synchronization control respectively. The simulation validation using Matlab/Simulink is performed

MMC Stored Energy Participation to the DC Bus Voltage Control in an HVDC Link

The modular multilevel converter (MMC) is becoming a promising converter technology for HVDC transmission systems. Contrary to the conventional two- or three-level VSC-HVDC links, no capacitors are connected directly on the dc bus in an MMC-HVDC link. Therefore, in such an HVDC link, the dc bus voltage may be much more volatile than in a conventional VSC-HVDC link. In this paper, a connection between the dc bus voltage level and the stored energy inside the MMC is proposed in order to greatly improve the dynamic behavior in case of transients. EMT simulation results illustrate this interesting property on an HVDC link study case