Modelling of a wind turbine with permanent magnet synchronous generator

This investigation presents the implementation and simulation of a Simulink-based controlled permanent magnet synchronous generator (PMSG) wind turbine in the dq0 reference frame. The model consists of a current control subsystem, a PMSG model, a mechanical subsystem, a pitch angle controller and a wind turbine model. The current control subsystem makes use of PI controllers governing the wind turbine speed, the direct and quadrature stator currents and the pitch angle of the turbine blades. The pitch angle controller measures the speed and the active power from the generator limiting both in case of high-speed wind conditions. In order to verify the functioning and the effectiveness of the proposed controllers, simulations- for different operation conditions- are presented and discussed

Power Density Maximization in Medium Frequency Transformers by Using Their Maximum Flux Density for DC–DC Converters

The medium frequency transformer (MTF) is a key component of various new DC&ndash DC converters that are designed for applications in modern electrical power grids at medium and high voltage. To attain the high performance that are necessary for targeting these applications, MFTs should have high power density and high efficiency as characteristics. For this endeavor, newly designed MFT procedures, which also take advantages of new core materials, are under investigation. Differently to other design proposals, most of which use conventional transformer design procedures based on equating core losses to copper conduction losses, in this paper, an MTF with a nanocrystalline (VITROPERM 500F) core is designed with a new procedure that is oriented in aiming the maximum flux density (Bmax). The characteristics of the MFTs that are obtained by using this procedure are compared with those of the MFTFs that are designed with a conventional procedure. The results show that by using the proposed technique, we get a 25% reduction in the winding size, a higher power density, and a lower MTF building cost while maintaining a high efficiency (&gt 98%). The design methodology is developed through a rigorous mathematical analysis that is verified with computer simulations in Matlab-Simulink and validated with experimental results from two MTF laboratory prototypes designed at a flux density of 0.9 T (75% Bmax) and 1.2 T (Bmax). Document type: Articl

Wide area control strategy for multiple VSC based DC-links interconnecting dispersed wind farms

The paper focuses on a power management scheme in a multi-terminal DC transmission systems for integration of large-scale wind farms spread over a wide area. The proposed power management scheme addresses the reliability concerns in a multi-terminal DC transmission system in case of the most severe fault conditions, such as permanent fault in DC link and open circuit fault at the terminal of the grid-side converter. The primary objective of the proposed scheme is to avoid lost of wind farms power in case permanent faults by providing an alternative path for the power flow through a redundant path. In case of DC faults resistive fault current limiters were used to suppress the current to a reasonable level to enable disconnection of the faulty line. To validate the proposed scheme, a computer model has been built in Matlab-Simulink. Transient and permanent DC link faults are considered in order to demonstrate the effectiveness of the proposed power management scheme

WIDE AREA CONTROL STRATEGY FOR MULTIPLE VSC-BASED DC LINKS INTERCONNECTING DISPERSED WIND FARMS

ABSTRAC

Fault Detection and Localization in Transmission Lines with a Static Synchronous Series Compensator

This paper proposes a fault detection and localization method for power transmission lines with a Static Synchronous Series Compensator (SSSC). The algorithm is based on applying a modal transformation to the current and voltage signals sampled at high frequencies. Then, the wavelet transform is used for calculating the current and voltage traveling waves, avoiding low frequency interference generated by the system and the SSSC. Finally, by using reflectometry principles, straightforward expressions for fault detection and localization in the transmission line are derived. The algorithm performance was tested considering several study cases, where some relevant parameters such as voltage compensation level, fault resistance and fault inception angle are varied. The results indicate that the algorithm can be successfully be used for fault detection and localization in transmission lines compensated with a SSSC. The estimated error in calculating the distance to the fault is smaller than 1% of the transmission line length. The test system is simulated in PSCAD platform and the algorithm is implemented in MATLAB software

Weaning from mechanical ventilation in intensive care units across 50 countries (WEAN SAFE): a multicentre, prospective, observational cohort study

International audienceBackground: Current management practices and outcomes in weaning from invasive mechanical ventilation are poorly understood. We aimed to describe the epidemiology, management, timings, risk for failure, and outcomes of weaning in patients requiring at least 2 days of invasive mechanical ventilation. Methods: WEAN SAFE was an international, multicentre, prospective, observational cohort study done in 481 intensive care units in 50 countries. Eligible participants were older than 16 years, admitted to a participating intensive care unit, and receiving mechanical ventilation for 2 calendar days or longer. We defined weaning initiation as the first attempt to separate a patient from the ventilator, successful weaning as no reintubation or death within 7 days of extubation, and weaning eligibility criteria based on positive end-expiratory pressure, fractional concentration of oxygen in inspired air, and vasopressors. The primary outcome was the proportion of patients successfully weaned at 90 days. Key secondary outcomes included weaning duration, timing of weaning events, factors associated with weaning delay and weaning failure, and hospital outcomes. This study is registered with ClinicalTrials.gov, NCT03255109. Findings: Between Oct 4, 2017, and June 25, 2018, 10 232 patients were screened for eligibility, of whom 5869 were enrolled. 4523 (77·1%) patients underwent at least one separation attempt and 3817 (65·0%) patients were successfully weaned from ventilation at day 90. 237 (4·0%) patients were transferred before any separation attempt, 153 (2·6%) were transferred after at least one separation attempt and not successfully weaned, and 1662 (28·3%) died while invasively ventilated. The median time from fulfilling weaning eligibility criteria to first separation attempt was 1 day (IQR 0–4), and 1013 (22·4%) patients had a delay in initiating first separation of 5 or more days. Of the 4523 (77·1%) patients with separation attempts, 2927 (64·7%) had a short wean (≤1 day), 457 (10·1%) had intermediate weaning (2–6 days), 433 (9·6%) required prolonged weaning (≥7 days), and 706 (15·6%) had weaning failure. Higher sedation scores were independently associated with delayed initiation of weaning. Delayed initiation of weaning and higher sedation scores were independently associated with weaning failure. 1742 (31·8%) of 5479 patients died in the intensive care unit and 2095 (38·3%) of 5465 patients died in hospital. Interpretation: In critically ill patients receiving at least 2 days of invasive mechanical ventilation, only 65% were weaned at 90 days. A better understanding of factors that delay the weaning process, such as delays in weaning initiation or excessive sedation levels, might improve weaning success rates. Funding: European Society of Intensive Care Medicine, European Respiratory Society