Control of a battery energy storage system to compensate for ADN equivalents inaccuracies

peer reviewedThis paper proposes a new application for a Battery Energy Storage System (BESS) connected at distribution level. It consists of controlling the BESS in such a way that the net active and reactive powers entering the distribution network matches as closely as possible the response of a dynamic equivalent model of the latter, used in large-disturbance dynamic simulations of the transmission system. Thus, the BESS compensates for the inevitable inaccuracies of the equivalent, which can be used with higher guarantee of accuracy. The battery is supposed to be available for other purposes at the main substation of the distribution grid. Its active and reactive powers are controlled without resorting to any model of that grid. Simulations results are reported on the CIGRE MV test system. Good performances are found in response to disturbances of various severities

Dynamic equivalent of a real distribution grid hosting photovoltaic and synchronous generators

peer reviewedThis paper presents a methodology to derive a reduced-order, “grey-box” model of an active distribution network. This dynamic equivalent is intended for dynamic simulations of large disturbances taking place in the transmission system. To deal with the uncertainty affecting dynamic model parameters, Monte-Carlo simulations are used, and the parameters of the equivalent are adjusted to match as close as possible the average randomized system responses. To avoid over-fitting, multiple disturbances are considered; they are automatically selected among a set of candidates. Moreover, to reduce the computational burden, only parameters with significant impact are adjusted in the identification procedure. Simulation results are reported on a real Australian distribution grid. The latter hosts synchronous generators and residential photovoltaic units. Its loads are modelled with a static and a motor part

Frequency Response from Solar PV: A Dynamic Equivalence Closed Loop System Identification Approach

peer reviewedAnalysis of the frequency response of integrated transmission-distribution networks with deep penetration of solar photovoltaic (PV) generation faces major challenges due to the complexity emerging from dynamic models of the numerous and diverse PV units involved. This work proposes converter-based dynamic equivalent models for both distributed (distribution network-connected) and large-scale (transmission network-connected) PV units which take into account practical issues such as measurement and coordination delays. Differently from previous work that adopted open-loop identification, the unknown model parameters are identified here through a novel closed-loop identification process based on least-square minimization. This allows capturing the continuous interaction between system and PV responses, thus improving the outcome of the overall frequency response model. The proposed models are validated with real data from the August 2018 separation event in Australia. The results demonstrate the excellent performance of the proposed models in determining the frequency response from PV in both transmission and distribution networks, hence paving the way to its adoption in frequency stability analysis in low-carbon grids dominated by frequency-responsive renewables

Molécules et contenants : l’importance du choix galénique

Les hamsters ne connaissent pas leur bonheur, eux qui bénéficient des nouveaux médicaments aux effets miraculeux cinq années avant les hommes.Philippe Bouvard Introduction En 2006, les patients âgés de 65 ans et plus représentaient 18 % des assurés belges, ils généraient 46 % des dépenses de soins de santé. Cette population pourrait atteindre, au vu de l’augmentation de l’espérance de vie, 26 % de la population en 2060. La combinaison de ces chiffres laisse présager d’une augmentation sensibl..

Modelling Active Distribution Networks under Uncertainty: Extracting Parameter Sets from Randomized Dynamic Responses

peer reviewedThis paper deals with the dynamic modelling of distribution systems hosting a large amount of Inverter-Based Generators (IBGs), more precisely their response to large disturbances in the transmission system. It is assumed that the individual behaviour of IBGs and loads is reasonably well captured by a parameterized model, but the values of its parameters are uncertain. Monte-Carlo simulations involving random variations of those parameters are performed. The dynamic response closest to the average is extracted as being representative. A simple procedure is described to stop the simulations as soon as sufficient information is available. Detailed simulation results are provided, relative to a distribution grid with 75 loads and 75 IBGs. The latter are represented by a generic model that reproduces the main requirements of typical grid codes

Molécules et contenants : l’importance du choix galénique

Les hamsters ne connaissent pas leur bonheur, eux qui bénéficient des nouveaux médicaments aux effets miraculeux cinq années avant les hommes.Philippe Bouvard Introduction En 2006, les patients âgés de 65 ans et plus représentaient 18 % des assurés belges, ils généraient 46 % des dépenses de soins de santé. Cette population pourrait atteindre, au vu de l’augmentation de l’espérance de vie, 26 % de la population en 2060. La combinaison de ces chiffres laisse présager d’une augmentation sensibl..

Reduced-order modelling of active distribution networks for large-disturbance simulations

Distribution systems are getting more and more complex owing to the increasing number of Inverter-Based Generators (IBGs) connected at Medium-Voltage (MV) level. This makes distribution networks more and more responsive and their influence on the whole power system dynamics increases. Therefore, it becomes important for Transmission System Operators (TSOs) to model those Active Distribution Networks (ADNs) in their dynamic studies. First, this thesis deals with the derivation of reduced-order, “grey-box” models of ADNs, intended for dynamic simulations of the transmission system. The ADNs are assumed to host IBGs as well as static and motor loads, whose dynamic parameters are affected by uncertainty. This latter issue is addressed using Monte-Carlo simulations. The parameters of the equivalents are adjusted to match as closely as possible the average of the randomized responses, while their dispersion is accounted for through the weights of the weighted least-square minimization. A procedure is used to remove from the identification the parameters with negligible impact. To avoid over-fitting, the equivalents are tuned for multiple large-disturbance simulations. A recursive procedure is used to select the smallest possible subset of disturbances involved in the least-square minimization. Next, the methodology is extended to account for changing operating conditions. This consists of testing the accuracy of a set of previously derived equivalents, and updating the best of them if its accuracy is not satisfactory. In order to update the equivalent with minimal effort, an approach minimizes the number of parameters to update. In most cases, the results coincide with expectations coming from “engineering judgment”, involving the adjustment of a (very) small subset of parameters. Finally, a new application for a Battery Energy Storage System (BESS), connected at distribution level, is proposed. Its active and reactive powers are controlled such that the net power entering the distribution network matches the response of the available equivalent to large disturbances in the transmission system. The response of the equivalent is simulated in real time. This would allow using with a higher guarantee of accuracy the equivalent model in dynamic simulations of the transmission system. The BESS is supposed to be connected at the main substation of the distribution grid and its control does not use any model of that grid. All simulations reported in the thesis have been carried out on three ADN test systems with different characteristics, one of them being derived from an existing distribution grid. The tests involve large disturbance scenarios that trigger nonlinear, discontinuous responses of IBGs and loads

Modélisation dynamique d'unité photovoltaïques en réponse à des perturbations de la tension

peer reviewedThe objective of this work was to build a simplified mathematical model of distributed photovoltaic (PV) units representing small-scale systems accounting for residential installations. These installations are generally connected to the Low Voltage (LV) network but can be aggregated to a Medium Voltage (MV) bus through equivalent impedance accounting for the distribution feeder and the transformer. The model represents reliably the dynamic behavior of small-scale PV units in response to grid voltage disturbances according to new connection requirements. It focuses on grid interactions through the electronic interface and does not propose a detailed mathematical representation of each physical component of the system. Therefore, the mathematical model is based on recent/near future grid requirements and ancillary services that should be provided by PV units to support the grid during a fault. The proceedings of this work can be divided in three parts. First, one third of the time has consisted in the review of the literature and grid codes to make out a list of PV model specifications. The most important specifications are the Low Voltage Ride- Through (LVRT) capability, the voltage support through reactive current injection and the active-reactive strategy during a fault. During the second third of the time, the dynamic model of PV units has been built based on existing elaborated models that have been improved in order to implement the PV model specifications. Finally, the remaining time has been devoted to dynamic simulations using a 75-bus MV test network where PV units have been attached to each node next to static and dynamic loads. The external transmission system has been represented by its Thevenin equivalent defined by its short circuit power. First, simulations have been made in order to validate the model. Then different scenarios interesting from a System Operator point of view have been investigated in order to see how the units react in particular fault/low voltage situations. The figure 1 shows the fast increase in PV units installed capacity around the world that clearly illustrates the needs in the introduction of new PV units grid requirements and in new models implementing these requirements

Aggregated Dynamic Equivalent of a Distribution System hosting Inverter-based Generators

peer reviewedAn equivalent, i.e. a reduced-order model, of active distribution networks is derived, for use in (phasor-mode) dynamic simulations of large-disturbances. In the unreduced model, the network hosts a large number of inverter-based generators, responding to the disturbances in accordance with recent or near-future grid codes. The aggregated equivalent is of the “grey-box” type and its parameters are tuned in the least-square sense to match the dynamic responses of the unreduced system to several training disturbances. Changes in operating point are easily reflected when initializing the reduced model. Simulations are reported on a detailed 75-bus distribution system. The accuracy of the equivalent has been checked with respect to untrained disturbances and changes of the operating point

Dynamic Equivalent of a Distribution Grid Hosting Dispersed Photovoltaic Units

peer reviewedThis paper deals with the derivation of a simplified model of a distribution network hosting dispersed photovoltaic units. The model is aimed at short-term dynamic simulations of a transmission grid in response to large disturbances. In a first step, a generic dynamic model of a photovoltaic unit is proposed, focusing on its interactions with the grid, in particular the controls triggered by voltage disturbances. The model takes into account various present and near-future grid codes. In a second step, a dynamic equivalent is derived accounting for the distribution network, the dispersed photovoltaic units, as well as static and dynamic (motor) loads. This equivalent is of the “grey-box” type and its parameters are tuned in the least-square sense to match the dynamic response of the original, unreduced system. Simulation results are reported on a detailed 913-bus distribution system subject to faults at transmission level