This article deals with the postfault synchronization of a voltage source converter based on the droop control. In the 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 article 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.
A reduced-order, "grey-box" model of an active distribution network, intended for dynamic simulations of the transmission system, is derived. The network hosts inverter-based generators as well as ...static and motor loads, whose dynamic parameters are affected by uncertainty. This issue is addressed using Monte-Carlo simulations. The parameters of the equivalent 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 equivalent is 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. Simulation results with a 75-bus MV test-system are reported. They show that the equivalent is able to reproduce with good accuracy the discontinuous controls of inverter-based generators, such as reactive current injection and tripping.
The proposed hierarchical secondary voltage control is a spatially distributed control system using communication networks which are disturbed by both a time delays and packet data dropouts. A state ...feedback integral control is adopted to eliminate the effect of non-zero disturbance and provide exact tracking of the references of the pilot points and alignment of the reactive powers of the generators that participate in the control. The system is modeled as a discrete-time switched system, and the control gains are synthesized by solving LMIs for a stability condition based on a state-dependent Lyapunov function. For that, the cone complementarity linearization (CCL) algorithm is used. The effectiveness of the proposed control strategy in preventing time delays and packet losses is simulated, considering the model of a realistic electric power grid under typical operational conditions using MATLAB.
Many engineering systems can be described by using differential models whose solutions, generally obtained after discretization, can exhibit a noticeable deviation with respect to the response of the ...physical systems that those models are expected to represent. In those circumstances, one possibility consists of enriching the model in order to reproduce the physical system behavior. The present paper considers a dynamical system and proposes enriching the model solution by learning the dynamical model of the gap between the system response and the model-based prediction while ensuring that the time integration of the learned model remains stable. The proposed methodology was applied in the simulation of the top-oil temperature evolution of a power transformer, for which experimental data provided by the RTE, the French electricity transmission system operator, were used to construct the model enrichment with the hybrid rationale, ensuring more accurate predictions.
In this paper, kinetic modeling techniques for complex chemical processes are reviewed. After a brief historical overview of chemical kinetics, an overview is given of the theoretical background of ...kinetic modeling of elementary steps and of multistep reactions. Classic lumping techniques are introduced and analyzed. Two examples of lumped kinetic models (atmospheric gasoil hydrotreating and residue hydroprocessing) developed at IFP Energies nouvelles (IFPEN) are presented. The largest part of this review describes advanced kinetic modeling strategies, in which the molecular detail is retained, i.e. the reactions are represented between molecules or even subdivided into elementary steps. To be able to retain this molecular level throughout the kinetic model and the reactor simulations, several hurdles have to be cleared first: (i) the feedstock needs to be described in terms of molecules, (ii) large reaction networks need to be automatically generated, and (iii) a large number of rate equations with their rate parameters need to be derived. For these three obstacles, molecular reconstruction techniques, deterministic or stochastic network generation programs, and single-event micro-kinetics and/or linear free energy relationships have been applied at IFPEN, as illustrated by several examples of kinetic models for industrial refining processes.
Dans cet article, les techniques de modélisation cinétique des processus chimiques complexes sont examinées. Après un bref aperçu historique de la cinétique chimique, un aperçu des bases théoriques de la modélisation cinétique d’étapes élémentaires et de réactions globales est présenté. Les techniques classiques de regroupement (lumping) sont ensuite présentées et analysées. Deux exemples de modèles cinétiques regroupés (pour l’hydrotraitement de gazole atmosphérique et pour l’hydrotraitement de résidus) développés à IFP Energies nouvelles (IFPEN) sont présentés. La plus grande partie de cette revue décrit des stratégies avancées de modélisation cinétique, dans lesquelles le détail moléculaire est retenu : les réactions entre les molécules sont représentées ou même subdivisées en étapes élémentaires. Pour être en mesure de conserver ce niveau moléculaire à la fois dans le modèle cinétique et dans les simulations de réacteurs, plusieurs obstacles doivent d’abord être éliminés : (i) la charge doit être décrite en termes de molécules, (ii) les grands réseaux réactionnels doivent être générés automatiquement et (iii) un grand nombre d’équations de vitesse avec leurs paramètres de vitesse doit être dérivé. Pour ces trois obstacles, des techniques de reconstruction moléculaire, des programmes de génération de réseaux déterministes ou stochastiques, et des modèles microcinétiques basés sur des événements constitutifs (single events) et/ou des relations linéaires d’énergie libre (Linear Free Energy Relationships) ont été utilisés à IFPEN, comme illustré par plusieurs exemples de modèles cinétiques pour des procédés de raffinage industriels.
This paper deals with the derivation of dynamic equivalents of active distribution networks, hosting inverter-based generators as well as static and motor loads. Equivalents are reduced-order models ...for use in dynamic simulations of the transmission system. They are of the grey-box types and their parameters are identified from large-disturbance Monte-Carlo simulations accounting for model uncertainty. After presenting an overview of the identification method at a single operating point, the paper deals with the update the equivalent when the operating conditions of the distribution network change. A procedure identifies the parameters to update, hence avoiding a complete new identification. Besides illustrative examples, two sets of simulation results are reported. First, the accuracy of the equivalent is validated in a long-term voltage instability scenario. Second, a larger-scale application is presented, with numerous instances of the equivalent attached to the model of the IEEE Nordic transmission test system. This combined model is used to assess the impact on short- and long-term voltage stability of the inverter-based generators with fast and slow controls.
Vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic (VEXAS) syndrome is an acquired autoinflammatory monogenic disease with a poor prognosis whose determinants are not well understood. We aimed ...to describe serious infectious complications and their potential risk factors.
Retrospective multicentre study including patients with VEXAS syndrome from the French VEXAS Registry. Episodes of serious infections were described, and their risk factors were analysed using multivariable Cox proportional hazards models.
Seventy-four patients with 133 serious infections were included. The most common sites of infection were lung (59%), skin (10%) and urinary tract (9%). Microbiological confirmation was obtained in 76%: 52% bacterial, 30% viral, 15% fungal and 3% mycobacterial. Among the pulmonary infections, the main pathogens were
2 (28%),
(21%) and
(19%). Sixteen per cent of severe infections occurred without any immunosuppressive treatment and with a daily glucocorticoid dose ≤10 mg. In multivariate analysis, age >75 years (HR (95% CI) 1.81 (1.02 to 3.24)),
mutation (2.29 (1.10 to 5.10)) and arthralgia (2.14 (1.18 to 3.52)) were associated with the risk of serious infections. JAK inhibitors were most associated with serious infections (3.84 (1.89 to 7.81)) compared with biologics and azacitidine. After a median follow-up of 4.4 (2.5-7.7) years, 27 (36%) patients died, including 15 (56%) due to serious infections.
VEXAS syndrome is associated with a high incidence of serious infections, especially in older patients carrying the
mutation and treated with JAK inhibitors. The high frequency of atypical infections, especially in patients without treatment, may indicate an intrinsic immunodeficiency.
Background
Long‐term treatment‐free remission (TFR) represents a new goal for chronic myeloid leukemia (CML). In clinical practice, tyrosine kinase inhibitor (TKI) dose reductions can be considered a ...means of preventing adverse effects and improving quality of life. We hypothesized that administration of low‐dose TKIs before treatment discontinuation does not impair TFR in patients with CML who have a deep molecular response (DMR, ≥MR4).
Methods
We conducted a retrospective analysis of 77 patients with CML who discontinued treatment with TKIs. Twenty‐six patients had been managed with low‐dose TKIs before stopping treatment. Patients were to be exposed to TKIs for ≥5 years and to low‐dose TKIs for ≥1 year and in DMR for ≥2 years. The loss of major molecular response (MMR) was considered a trigger for restarting therapy.
Results
In the low‐dose group, 61.5% of patients received second‐generation TKIs, and dose reduction was ≥50% for 65.4% of patients. With a median follow‐up of 61.5 months, TFR at 12 months was 56.8% in the full‐dose TKI group and 80.8% in the low‐dose group, and TFR at 60 months was 47.5% and 58.8%, respectively. The median time to molecular recurrence (≥MMR) from TKI discontinuation in the entire cohort was 6.2 months. All patients quickly achieved MMR after resuming TKI therapy. Results appear independent of both dose reduction and potential pretreatment with interferon‐α.
Conclusion
This retrospective study shows that TFR was not impaired by low‐dose TKI regimens before TKI cessation in Patients with CML. Nevertheless, prospective randomized clinical trials must be undertaken to analyze the probability of successful TFR in patients managed with TKI dose de‐escalation strategies before TKI discontinuation.
We conducted a retrospective analysis of chronic myeloid leukemia patients who had been managed with low‐dose tyrosine kinase inhibitors (TKIs) and discontinued treatment to test the hypothesis that treatment‐free remission was not impaired by low‐dose TKI regimens (≥1 year) before treatment cessation.
To describe the characteristics and the outcome of primary Sjögren Syndrome (pSS) associated arthritis and to compare the efficacy of different therapeutic regimen.
We conducted a retrospective study ...using Club Rhumatisme and Inflammation (CRI) and French Internal Medicine Society (SNFMI) networks. All patients with a diagnosis of pSS and at least one episode of clinical and/or echographic synovitis were included. Patients with synovitis (cases) were compared to pSS patients without synovitis (controls).
57 patients (93% women) were included with a median age of 54 years 45–63. Patients with synovitis had more frequently lymph node enlargement (12.3% vs. 1.8%, p = .007) and a higher ESSDAI score (8 6–12 vs. 2 1–4, p < .0001). There was no difference concerning CRP levels, rheumatoid factor and cyclic citrullinated peptide (CCP)-antibodies positivity. Among 57 patients with synovitis, 101 various treatment courses have been used during the follow-up of 40 22.5–77 months. First treatment course consisted in steroids alone (3.5%), steroids in association (79%) with hydroxychloroquine (HCQ) (49%), methotrexate (MTX) (35%), rituximab (RTX) (5.3%) or other immunosuppressive drugs (7%). HCQ, MTX, and RTX were associated with a significant reduction of tender and swollen joint count, and a significant steroids-sparing effect. No difference could be shown for the joint response between these treatment regimens.
pSS articular manifestations may include synovitis which could mimic rheumatoid arthritis but differ by the absence of structural damage. Even if the use of HCQ, MTX, and RTX seem to be effective for joint involvement, the best regimen remains to be determined.
We investigated whether partitioning DLCO into membrane conductance for CO (DmCO) and pulmonary capillary blood volume (Vcap) was helpful in suspecting precapillary pulmonary (arterial) hypertension ...(P(A)H) in systemic sclerosis (SSc) patients with or without interstitial lung disease (ILD). We included 63 SSc patients with isolated PAH (n=6), isolated ILD (n=19), association of both (n=12) or without PAH and ILD (n=26). Partitioning of DLCO was performed by the combined DLNO/DLCO method. DLCO, DmCO and Vcap were equally reduced in patients with isolated PAH and patients with isolated ILD but Vcap/alveolar volume (VA) ratio was significantly lower in the isolated PAH group. In patients without ILD, DLCO, DmCO, Vcap and Vcap/VA ratio were reduced in patients with isolated PAH when compared to patients without PAH and both Vcap/VA and DLCO had the highest AUC to detect PAH. In patients with ILD, Vcap had the highest AUC and performed better than DLCO to detect PH in this subgroup. In conclusion, Vcap/VA was lower in PAH than in ILD in SSC whereas DLCO was not different. Vcap/VA ratio and DLCO had similar high performance to detect PAH in patients without ILD. Vcap had better AUC than DLCO, DmCO and FVC/DLCO ratio to detect PH in SSC patients with ILD. These results suggest that partitioning of DLCO might be of interest to detect P(A)H in SSC patients with or without ILD.
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