The Experts below are selected from a list of 8607 Experts worldwide ranked by ideXlab platform

Zheng Xu - One of the best experts on this subject based on the ideXlab platform.

  • Coordinated control of wind farm and VSC–HVDC system using capacitor energy and kinetic energy to improve inertia level of power systems
    International Journal of Electrical Power & Energy Systems, 2014
    Co-Authors: Yujun Li, Yingyi Li, Hairong Chen, Zeren Zhang, Yong Yang, Zheng Xu
    Abstract:

    Abstract For large-scale offshore wind power integration to main grids over a long distance, the VSC–HVDC transmission is a typical way. However, the asynchronous characteristic of HVDC link leads to the frequency decouple of the offshore grid and the main grid, i.e., the offshore grid has little or no inertia support for the main grid. The high level penetration of wind energy makes the main grid an “inertia-less” system and impairs the overall stability of the system. This paper proposes a new coordinated control strategy which uses the electrical energy stored in the DC capacitors and the kinetic energy stored in wind turbine rotors to emulate the inertia of synchronous generators. By this control strategy, the DC link capacitors release or absorb energy following the droop DC voltage control of the grid side VSC (GSVSC), and the wind farm VSC (WFVSC) changes its output frequency according to the DC voltage. Thus, an artificial coupling of the frequencies of the two-side AC systems is obtained without remote communication. According to the WFVSC’s output frequency, the wind turbine power controller alters its power reference, and the wind turbine speed changes. Thus, the kinetic energy stored in wind turbine rotors is absorbed or released. As a result, the wind turbine is utilized to keep the main grid frequency stable. Based on the doubly fed induction generator (DFIG) wind turbine, this paper analyzes the influence of different additional power controllers and different control parameters of the proposed control strategy on the inertia time constant. Within the Permissible Range of the DC voltage variation, the proposed control strategy can provide a wide Range of inertia time constant, which improves the overall stability of the main grid system. Simulation results of three operation conditions, i.e., sudden load changes, variation of the wind speed, and AC system faults, validated the effectiveness of the proposed coordinated control strategy.

Shalabh C. Maroo - One of the best experts on this subject based on the ideXlab platform.

  • Steady State Vapor Bubble in Pool Boiling.
    Scientific Reports, 2016
    Co-Authors: An Zou, Ashish Chanana, Amit Agrawal, Peter C. Wayner, Shalabh C. Maroo
    Abstract:

    Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain Permissible Range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics.

Yujun Li - One of the best experts on this subject based on the ideXlab platform.

  • Coordinated control of wind farm and VSC–HVDC system using capacitor energy and kinetic energy to improve inertia level of power systems
    International Journal of Electrical Power & Energy Systems, 2014
    Co-Authors: Yujun Li, Yingyi Li, Hairong Chen, Zeren Zhang, Yong Yang, Zheng Xu
    Abstract:

    Abstract For large-scale offshore wind power integration to main grids over a long distance, the VSC–HVDC transmission is a typical way. However, the asynchronous characteristic of HVDC link leads to the frequency decouple of the offshore grid and the main grid, i.e., the offshore grid has little or no inertia support for the main grid. The high level penetration of wind energy makes the main grid an “inertia-less” system and impairs the overall stability of the system. This paper proposes a new coordinated control strategy which uses the electrical energy stored in the DC capacitors and the kinetic energy stored in wind turbine rotors to emulate the inertia of synchronous generators. By this control strategy, the DC link capacitors release or absorb energy following the droop DC voltage control of the grid side VSC (GSVSC), and the wind farm VSC (WFVSC) changes its output frequency according to the DC voltage. Thus, an artificial coupling of the frequencies of the two-side AC systems is obtained without remote communication. According to the WFVSC’s output frequency, the wind turbine power controller alters its power reference, and the wind turbine speed changes. Thus, the kinetic energy stored in wind turbine rotors is absorbed or released. As a result, the wind turbine is utilized to keep the main grid frequency stable. Based on the doubly fed induction generator (DFIG) wind turbine, this paper analyzes the influence of different additional power controllers and different control parameters of the proposed control strategy on the inertia time constant. Within the Permissible Range of the DC voltage variation, the proposed control strategy can provide a wide Range of inertia time constant, which improves the overall stability of the main grid system. Simulation results of three operation conditions, i.e., sudden load changes, variation of the wind speed, and AC system faults, validated the effectiveness of the proposed coordinated control strategy.

And A Persad - One of the best experts on this subject based on the ideXlab platform.

  • use of computational fluid dynamics as a tool for establishing process design space for mixing in a bioreactor
    Biotechnology Progress, 2012
    Co-Authors: Anurag S Rathore, C Sharma, And A Persad
    Abstract:

    The concept of “design space” plays an integral part in implementation of quality by design for pharmaceutical products. ICH Q8 defines design space as “the multidimensional combination and interaction of input variables (e.g., material attributes) and process parameters that have been demonstrated to provide assurance of quality. Working within the design space is not considered as a change. Movement out of the design space is considered to be a change and would normally initiate a regulatory post-approval change process. Design space is proposed by the applicant and is subject to regulatory assessment and approval.” Computational fluid dynamics (CFD) is increasingly being used as a tool for modeling of hydrodynamics and mass transfer. In this study, a laboratory-scale aerated bioreactor is modeled using CFD. Eulerian-Eulerian multiphase model is used along with dispersed k–e turbulent model. Population balance model is incorporated to account for bubble breakage and coalescence. Multiple reference frame model is used for the rotating region. We demonstrate the usefulness of CFD modeling for evaluating the effects of typical process parameters like impeller speed, gas flow rate, and liquid height on the mass transfer coefficient (kLa). Design of experiments is utilized to establish a design space for the above mentioned parameters for a given Permissible Range of kLa. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2012

Anurag S Rathore - One of the best experts on this subject based on the ideXlab platform.

  • optimization of a refolding step for a therapeutic fusion protein in the quality by design qbd paradigm
    IEEE Journal of Solid-state Circuits, 2012
    Co-Authors: Pratap D Bade, Susmitha Purnima Kotu, Anurag S Rathore
    Abstract:

    Production of biotech therapeutics in Escherichia coli involves protein expression as insoluble inclusion bodies that need to be denatured and the resulting protein refolded into the native structure. In this paper, we apply a Quality by Design approach using Design of Experiments for optimization of the refolding process for a recombinant biotech therapeutic, granulocyte colony stimulating factor. First, risk analysis was performed to identify process parameters that require experimental examination. Next, the chosen parameters were examined using a fractional factorial screening design. Based on the results of this study, parameters that have significant effect on refold yield and product quality were identified and examined using a full factorial Design of Experiments for their interactions. The final model was statistically significant and delivered a refolding yield of 77%. Further, kinetics of refolding was evaluated under optimal conditions and was found to be of first order with a rate constant of 0.132/min. Design space was established for the three parameters for a given Permissible Range of yield, protein concentration, and purity. The primary objective of this paper is to provide a roadmap for implementing Quality by Design for development of a protein refolding step.

  • use of computational fluid dynamics as a tool for establishing process design space for mixing in a bioreactor
    Biotechnology Progress, 2012
    Co-Authors: Anurag S Rathore, C Sharma, And A Persad
    Abstract:

    The concept of “design space” plays an integral part in implementation of quality by design for pharmaceutical products. ICH Q8 defines design space as “the multidimensional combination and interaction of input variables (e.g., material attributes) and process parameters that have been demonstrated to provide assurance of quality. Working within the design space is not considered as a change. Movement out of the design space is considered to be a change and would normally initiate a regulatory post-approval change process. Design space is proposed by the applicant and is subject to regulatory assessment and approval.” Computational fluid dynamics (CFD) is increasingly being used as a tool for modeling of hydrodynamics and mass transfer. In this study, a laboratory-scale aerated bioreactor is modeled using CFD. Eulerian-Eulerian multiphase model is used along with dispersed k–e turbulent model. Population balance model is incorporated to account for bubble breakage and coalescence. Multiple reference frame model is used for the rotating region. We demonstrate the usefulness of CFD modeling for evaluating the effects of typical process parameters like impeller speed, gas flow rate, and liquid height on the mass transfer coefficient (kLa). Design of experiments is utilized to establish a design space for the above mentioned parameters for a given Permissible Range of kLa. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2012