Single-sided linear induction motors (SLIMs) have lately been applied in transportation system traction drives, especially in the intermediate speed range. They have merits such as the ability to exert thrust on the secondary without mechanical contact, high acceleration or deceleration, less wheel wear, small turning circle radius and flexible road line. The theory of operation for these machines can be directly derived from rotary induction motors, but several issues involving the transversal edge and the longitudinal end effects, and half-filled slots at the primary ends, need to be investigated. In this paper, a T model equivalent circuit is proposed which is based on onedimensional magnetic equations of the air-gap, where half-filled slots are considered by an equivalent pole number. Then, it deduces two-axis equivalent circuits to study the SLIM dynamic performance. The theoretical analyses have been validated by experimental results on SLIM prototypes.
An integrated controller of wind turbines with both inertial response and primary frequency regulation (PFR) to provide complete dynamic frequency support for the grid with high wind power penetration is investigated. The wind turbine control governor contains two cross-coupled controllers: pitch controller and maximum power point tracking (MPPT) controller. First, as a precondition for the PFR, a de-loading pitch control scheme is proposed to reserve capacity required for frequency regulation. Then, by optimizing the MPPT scheme, the rapid virtual inertia response is achieved even under de-loading operation condition. Based on the analysis of the steady-state characteristics of wind turbines with frequency droop control, the primary frequency control strategy, which enables the adjustment of frequency droop coefficient, is further proposed through pitch angle changes. Thus, the PFR and inertial response can be both achieved by the proposed de-loading pitch controller and optimized MPPT controller. A three-machine prototype system containing two synchronous generators and a Doubly Fed Induction Generator (DFIG)-based wind turbine with 30% of wind penetration is implemented to validate the proposed integrated control strategies on providing inertial response and subsequent load sharing in the event of frequency change.
This version is available at https://strathprints.strath.ac.uk/53537/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: firstname.lastname@example.orgThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.This paper is a post-print of a paper submitted to and accepted for publication in IEEE Transaction on Power Delivery and is subject to Institution of Electrical and Electronic Engineering Copyright. The copy of record is available at IEEE Xplore Digital Library.1 Abstract-This paper presents the control and operation of a hybrid HVDC system comprising a wind farm side VSC rectifier and a grid side LCC inverter for integrating wind power. The configuration and operation principle of the hybrid HVDC system are described. Commutation failure in the LCC inverter during an AC network disturbance is considered and its impact on the hybrid system operation is analyzed. An enhanced control strategy for the LCC inverter at the grid side and an alternative MMC topology using mixed half-bridge and full-bridge modules considered for the rectifier at the wind farm side are proposed. Simulation results using Matlab/Simulink are presented to demonstrate the robust performance during LCC inverter commutation failure to validate the operation and recovery of the hybrid system with the proposed control strategy and MMC configuration.Index Terms-Commutation failure, hybrid HVDC, LCC, MMC, VSC, wind farm. I. INTRODUCTIONLarge wind farms both onshore (e.g. in China) and offshore (e.g. in Europe) have been developed with more being planned. Many of the large wind farms are located long distance away from the load centers or the available connection points. In cost-benefit terms, HVDC is likely to be preferable to HVAC technology for the main connection of large offshore wind farms when cable lengths exceed 80-120 km. For connecting large onshore remote wind farms using overhead lines, HVDC also provides significant benefits in terms of flexible control and improved system stability, and reduced cost for transmission distance over 600...
The transport and uptake of individual propranolol (PPL) enantiomers were studied in human intestinal Caco-2 cell monolayers, and a reversed-phase HPLC-UV assay was used for quantitative analysis. S-PPL and R-PPL across Caco-2 cell monolayers was determined in the concentrations range of 10-500 microM in both apical (AP) to basolateral (BL) and BL to AP directions. S-PPL exhibited greater permeability than R-PPL in the AP to BL direction, whereas in the BL to AP direction S-enantiomer transported less than R-enantiomer. Uptake of R-PPL was significantly higher than that of S-PPL either from AP side or from BL side. The statistically significant differences in uptake were observed at the concentrations range from 10 to 50 microM. Furthermore, the apparent Michaelis constant (K(m)) and maximal velocity (V(max)) also showed significant difference between the two enantiomers. Moreover, the AP to BL transport of PPL enantiomer was markedly decreased by lowering the pH of the apical side but it did not affect the stereoselectivity of PPL across Caco-2 cell monolayers. The transport and uptake of PPL in the BL to AP direction was not influenced by several protein inhibitors. The results suggest that PPL enantiomers showed stereoselective transport and uptake across the Caco-2 cell monolayers. A special transport mechanism capable of directing the PPL enantiomers might be present in the Caco-2 monolayers.
Abstract-For modular multilevel converters (MMCs) applied to medium-voltage DC distribution grids, using the traditional Nearest Level Modulation (NLM) as in HVDC systems can lead to severe current distortion due to significantly reduced module number. This paper proposes a hybrid modulation method combining NLM and Pulse Width Modulation (PWM) where only one module per arm operates under PWM mode. The proposed Nearest Level PWM (NL-PWM) method not only significantly reduces the current distortion, but also avoids the complicated voltage balancing control in each module. The harmonic characteristics of NL-PWM are derived using double Fourier transform, which provides theoretical basis for selecting module number and switching frequency for medium-voltage application in accordance with grid harmonic requirements. Finally, the harmonic characteristics and feasibility of the proposed modulation method are validated by simulation and experimental studies on a MMC with 6 modules per arm. The simulated and experimental results reveal that NL-PWM has better voltage and current harmonic characteristics over NLM and CPS-PWM, thereby suiting the application of MMC with few models.
Abstract-In a DC grid, the inherent inertial support from the DC capacitors is too small to resist step changes or random fluctuations from the intermittent power resources, which results in lower DC voltage quality. In this paper, an adaptive droop control (ADC) strategy is proposed to achieve an increased inertia from the droop controlled converter.
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