Multi-terminal High-Voltage Direct-Current (MT-HVDC) Voltage Source Converter (VSC) based grids are arising as an extension of point-to-point connections, aiming at boosting the integration of ...renewable energy resources through a more interconnected power system. This paper investigates and compares different energy-based control structures for Modular Multilevel Converters (MMC) operating in DC voltage droop control mode, identifying the most suitable ones in terms of stability. Then, a systematic, automatic and optimal control design based on H∞ for a generic and bidirectional MT-HVDC system, including multiple DC voltage droop controlled terminals, is developed, based on both steady-state and transient requirements under different contingencies.
•DC voltage droop control structures comparison for MMCs in multi-terminal HVDC networks.•Systematic optimal control tuning method based on H∞.•Combination of steady-state and transient requirements.•Converters with different power ratings and bidirectional operation (generation, load).
This paper addresses the impact of the modular multilevel converter (MMC) energy control in the system dynamics when grid-forming and grid-following control schemes are used in the same system. The ...MMC total energy control can be implemented in different approaches. Depending on the control architecture and the level of energy buffering capability the MMC can be used to mitigate the propagation of disturbances from the AC to the DC side and vice-versa. In order to study the effect of this MMC capability in the system dynamics and interactions, a point-to-point link including one grid-forming and one grid-following converter is studied in detail for four different energy-based control architectures combinations. In order to compare them, two eigenproperties indices have been derived. The first index quantifies the participation of the eigenvalues in the system response and the second one, quantifies which states rule on the system dynamics. This study is accompanied with detailed nonlinear models implemented in MATLAB Simulink used to verify the results via time-domain simulations.
•Impact analysis of the MMC internal energy control on the system dynamics•Present an index that quantifies which states rule on the system dynamics•Present an index that quantifies the participation of an eigenvalue in the system response•Analysis four MMC control schemes combination•The effect of the energy controller gains are investigated for four different control schemes and different types of disturbances
•New controller based on resonant non-integer orders.○The experimental test involves balanced and non-balanced situations.•The non-integer order generates a new degree of freedom in the controller ...with high dynamic skills.•This controller emerges as a good option to be implemented in systems in which computational time is critical and memory dependence is important.
This paper proposes a novel fractional proportional-resonant controller, which applies fractional order calculus to the well-known proportional-resonant controllers. The focus of the study is the current control loop of voltage source converters. The main merit of the proposed fractional controller formulation lies into the use of fractional exponents in the integro-derivative parts obtaining a controller with an extra degree of freedom. This degree of freedom allows the phase delay to be improved for a wide frequency range in comparison with the conventional proportional-resonant controllers. Furthermore, the obtained controller results in a lower order transfer function that reduces the computational burden when multiple current frequencies have to be tracked. As fractional integro-derivative exponents are not directly implementable, five mathematical approaches are explored, selecting the Chareff’s approximation for the fractional controller operator’s implementation. A tuning procedure for such a controller is also addressed. The new controller formulation is validated in a 20kVA laboratory set-up based on a silicon-carbide converter, and it is implemented in a DSP. Two AC output converter’s configurations are considered to demonstrate the controllers’ tracking capability; short-circuited (balanced fault) output, and grid-connected operation. This last case is evaluated operating as active filter and delivering fundamental component to a non-ideal grid.
This paper suggests a methodology for the identification, classification, and evaluation of various types of interactions that may occur in an HVDC link based on modular multi-level converters (MMC). ...The methodology incorporates the most suitable analytic tools for the frequency-domain study of each interaction category. To do so, a detailed nonlinear model of an MMC-based HVDC link that consists of master and slave MMCs, AC grids, and the DC transmission system is derived. Then, it is linearized to obtain a multi-input multi-output (MIMO) linear model that represents the dynamics of the complete MMC-based HVDC link. Based on the control loops of interest, interactions are classified as (1) state variable interactions, (2) disturbance interactions, (3) control loop interactions, and (4) overall system interactions. Then, through the application examples, the mentioned four categories of interactions are studied in frequency domain via the relevant analytic tools. The results obtained from the frequency-domain analysis are validated by time-domain simulation.
•A methodology for evaluation of interactions in HVDC systems is suggested•Interactions caused by the cable parameters can destabilize the system•DC voltage control loop and total energy control loops are highly coupled•Active power loop is decoupled from DC voltage and total energy control loops
This paper investigates the dynamic behavior of a modular multi-level converter (MMC)-based HVDC link. An overall state-space model is developed to identify the system critical modes, considering the ...dynamics of the master MMC and slave MMC, their control systems, and the HVDC cable. Complementary to the state-space model, an impedance-based model is also derived to obtain the minimum phase margin (PM) of the system. In addition, a relative gain array (RGA) analysis is conducted to quantify the level of interactions among the control systems of master and slave MMCs and their impacts on stability. Finally, with the help of the results obtained from the system analysis (eigenvalue, phase margin, sensitivity, and RGA), the system dynamic performance is improved.
The glucagon-like peptide-1 receptor agonist family together with the renal sodium/glucose cotransporter-2 inhibitors have garnered interest as potential therapeutic agents for subjects with type 2 ...diabetes and obesity. In these patients, bariatric surgery is indicated based in a BMI ≥ 35 kg/m
. A 24-week non-blinded, randomized pilot study to assess the efficacy of subcutaneous exenatide 2.0 mg once weekly plus oral dapagliflozin 10 mg once daily (Group A) compared to a control group (Group B) in 56 patients with type 2 diabetes awaiting bariatric surgery was conducted (EudraCTid.: 2017-001,454-33). Both groups received an energy-deficit low-fat diet. The primary endpoint was the proportion of patients running off the criteria for bariatric surgery at the end of the follow-up period (BMI ≤ 35.0 kg/m
or a BMI ≤ 40.0 kg/m
plus an HbA1c ≤ 6.0%). Changes in the BMI were also of interest. The proportion of patients who ran off the criteria for bariatric surgery was larger in Group A than in the control group (45.8% vs. 12.0%, p = 0.010). Participants in Group A exhibited an absolute decrease in body weight and BMI of 8.1 kg (95%IC: - 11.0 to - 5.2) and 3.3 kg/m
(95%IC: - 4.5 to - 2.2), respectively (p < 0.001 for both in comparison with Group B). A higher percentage of participants in Group A reached a BMI < 35 kg/m
(45.8 vs 12.0%) and lost > 10% of their initial body weight (20.8 vs 0%) compared to Group B. The combination of exenatide plus dapagliflozin appears as a strategic option to reduce the waiting list for bariatric surgery, especially in those patients with type 2 diabetes.
The increase in sedentary behaviors during the COVID-19-induced lockdown may have led to a significant weight gain. To investigate this hypothesis, a representative sample of the Spanish adult ...population comprising 1000 subjects was enrolled in a cross-sectional study between 26 May and 10 June 2020. Computer-assisted telephone interviews were conducted consisting of 29 questions on the topic of lifestyle habits during the lockdown. The cohort comprised 51.5% women and 51% overweight or obese subjects and had a mean age of 50 ± 18 years. Of the respondents, 44.5% self-reported weight gain during the lockdown; of these, 58.0% were women, 69.9% had previous excess weight, 44.7% lived with a relative who also gained weight, and 73.5 experienced increased appetite. Further, an increased consumption of energy-dense products was found relative to respondents who did not gain weight (
≤ 0.016 for all). Additionally, respondents were unaware that obesity is a poor prognostic factor for COVID-19 infection, lived in smaller flats, and had a lower level of education and lower monthly income. The factors independently associated with weight gain were female gender, previous overweight or obesity, lack of food care, increased appetite, and increased consumption of sugar-sweetened beverages, alcoholic beverages, and snacks (
≤ 0.023 for all). Should another lockdown be mandated, extra caution is warranted to prevent weight gain.
Analysis of MMC Energy-Based Control Structures for VSC-HVDC Links Sanchez-Sanchez, Enric; Prieto-Araujo, Eduardo; Junyent-Ferre, Adria ...
IEEE journal of emerging and selected topics in power electronics,
09/2018, Letnik:
6, Številka:
3
Journal Article, Publication
Recenzirano
Odprti dostop
An analysis of control structures for modular multilevel converters (MMCs) used in high-voltage direct current (HVDC) applications is addressed. In particular, this paper focuses on the case of a ...point-to-point link with master-slave control, considering an energy-based scheme (also known as closed loop or energy controlled) for the MMC, meaning that the internal energy of the converter is explicitly controlled. With such an approach, the MMC internal energy can be controlled independently of the energy of the HVDC link, and whereas the internal capacitance of the MMC depends on the converter's rating, the capacitance at the dc terminal depends on the cable length. Therefore, several possibilities regarding the outer control structure (internal energy and dc voltage) arise, affecting the overall dynamics differently. Whereas for a long link, the classic control structures should perform well, for shorter links the transient performance might not be acceptable and other alternatives shall be used instead. Different control structures are presented and evaluated in this paper through small-signal and frequency-domain analysis, and validated through time-domain simulation with MATLAB Simscape Power Systems.
Recent environmental policies have led academic, industrial, and governmental stakeholders to plan scenarios with a high share of renewable energy sources (RES), to ensure that future energy systems, ...composed mostly of RES, can remain stable, match the demand during seasonal variations and are economically feasible. This article considers different energy scenarios to obtain various options in terms of size, generation technologies, and grid configuration. The scenarios are studied in the POSYTYF project and are quantified through an optimization‐based algorithm, where the test grids topologies are based on specific locations in Europe, and real data related to the availability of RES, as well as the demand. Different RES technologies are considered to meet requirements of grid integration of renewables at different horizons of time, up to 100% in the most futuristic case. The optimization algorithm is applied to three scenarios. It is shown that solar photovoltaic (PV) and wind can provide the renewable backbone, but they lack flexibility to achieve a very high share in the energy mix. Solar thermal and pumped hydro become important to cover the last range of integration, as they provide high flexibility, which is crucial for high share, but they are expensive for low share.
Recent environmental policies have led to increasing planning of scenarios with a high share of renewable energy sources (RES), to ensure that future RES‐based systems can remain stable, match the demand during seasonal variations, and are economically feasible. This article considers different energy scenarios to obtain various options in terms of size, generation technologies, and grid configuration.
Purpose
Adherence to Mediterranean diet (MedDiet) and physical activity have been associated to lower cardiovascular risk and mortality. Our purpose was to test the modification of advanced glycation ...end-products (AGEs) as one of the underlying mechanisms explaining this relationship.
Methods
Cross-sectional study assessing the adherence to MedDiet (14-item Mediterranean Diet Adherence Screener) and physical activity (International Physical Activity Questionnaire short form) in 2646 middle-aged subjects without known cardiovascular disease and type 2 diabetes from the ILERVAS study. Skin autofluorescence (SAF), a non-invasive assessment of subcutaneous AGEs, was measured. Multivariable logistic regression models were done to study interactions and independent associations with a likelihood ratio test.
Results
Participants with a high adherence to MedDiet had lower SAF than those with low adherence (1.8 IR 1.6; 2.1 vs. 2.0 IR 1.7; 2.3 arbitrary units,
p
< 0.001), without differences according to categories of physical activity. There was an independent association between high adherence to MedDiet and the SAF values OR 0.59 (0.37–0.94),
p
= 0.026. When adherence to MedDiet was substituted by its individual food components, high intake of vegetables, fruits and nuts, and low intake of sugar-sweetened soft beverages were independently associated with a decreased SAF (
p
≤ 0.045). No interaction between MedDiet and physical activity on SAF values was observed except for nuts consumption (
p
= 0.047).
Conclusions
Adherence to the MedDiet, but not physical activity, was negatively associated to SAF measurements. This association can be explained by some typical food components of the MedDiet. The present study offers a better understanding of the plausible biological conditions underlying the prevention of cardiovascular disease with MedDiet.
ClinTrials.gov identifier: NCT03228459.
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