scholarly journals Phase-Controlled Thyristor Sub-Synchronous Damper Converter for a Liquefied Natural Gas Plant

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5238
Author(s):  
Lorenzo Bongini ◽  
Rosa Anna Mastromauro ◽  
Daniele Sgrò ◽  
Fabrizio Malvaldi
Keyword(s):  
Control System ◽  
Natural Gas ◽  
High Performance ◽  
Reference Signal ◽  
Liquefied Natural Gas ◽  
Torsional Vibrations ◽  
Successful Operation ◽  
Torsional Instability ◽  
The Stability ◽  
Plant Configuration

In electrified liquefied natural gas (LNG) plants variable frequency drives (VFDs) interact with turbine-generator (TG) units creating torsional vibrations known as sub-synchronous torsional interactions (SSTIs). Torsional vibrations can be dangerous for an LNG plant when they involve torsional instability. The stability of an LNG plant depends on the plant configuration and on the number of TG units and of VFDs. In such peculiar configurations stability cannot be achieved acting of the VFDs control system. Alternatively, dedicated equipment is needed to damp the torsional vibrations. In this paper, a sub-synchronous damper (SSD) converter is used to mitigate the SSTI phenomena. The SSD converter consists of a thyristor H-bridge regulating the phase of the additional torque provided at the TG unit air-gap. A phase control system is proposed and is based on the torsional torque oscillations measurement. An adaptive reference signal is employed, also guaranteeing high performance in island-mode operation. The proposed solution increases the damping of the LNG plant in all the considered configurations. The LNG plant successful operation is validated by comprehensive results.

scholarly journals Electrical Damping Assessment and Stability Considerations for a Highly Electrified Liquefied Natural Gas Plant

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2612
Author(s):  
Lorenzo Bongini ◽  
Rosa Anna Mastromauro ◽  
Daniele Sgrò ◽  
Fabrizio Malvaldi
Keyword(s):  
Control System ◽  
Natural Gas ◽  
Gas Turbines ◽  
Ad Hoc ◽  
Power Converters ◽  
Liquefied Natural Gas ◽  
Variable Frequency ◽  
Torsional Vibrations ◽  
Variable Frequency Drives ◽  
Electrical Damping

In recent years, the Oil & Gas industry has been subjected to a progressive electrification process aiming to comply with global environmental requirements on CO2 emissions reduction. High-power electric motors fed by Variable Frequency Drives (VFDs) have replaced gas turbines as drivers for gas compression applications. In Liquefied Natural Gas (LNG) plants, unexpected downturns could be experienced in case of high torsional vibrations of power generations units. These torsional vibrations derive from the interaction among turbine-generator (TG) units and VFDs and are known as Sub-Synchronous Torsional Interactions (SSTIs). SSTIs can lead to instability when the overall electromechanical system lacks sufficient damping. In this scenario, electrical damping assessment is fundamental in order to ensure stability and reliable operation of an LNG plant. Negative electrical damping is strictly related to the negative incremental resistance behavior of the power converters and it is influenced by the converter’s control system. In this paper, a real case study based on Thyristor Variable Frequency Drives (TVFDs) is considered. Ad hoc dynamic models of the power converters and of the TG unit are developed and combined in order to provide an accurate estimation of the electrical damping. It is demonstrated that the electrical damping is affected by variations of the main control system parameters and how the use of a simplified model instead of an ad hoc model can impact the stability evaluation.

scholarly journals Electrical Damping Assessment and Sensitivity Analysis of a Liquefied Natural Gas Plant: Experimental Validation

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4084
Author(s):  
Lorenzo Bongini ◽  
Rosa Anna Mastromauro ◽  
Daniele Sgrò ◽  
Fabrizio Malvaldi
Keyword(s):  
Sensitivity Analysis ◽  
Control System ◽  
Natural Gas ◽  
Experimental Validation ◽  
Power Conversion ◽  
Liquefied Natural Gas ◽  
Fine Tuning ◽  
Simulation Platform ◽  
Electrical Damping ◽  
Conversion Stage

Liquefied Natural Gas (LNG) plants are commonly island-operated weak grids where the interaction of high-power Variable Frequency Drives (VFDs) with the Turbine-Generator (TG) units might cause Sub-Synchronous Torsional Interaction (SSTI) phenomena. SSTI phenomena can lead the LNG plant to instability conditions. Each LNG plant configuration is characterized by a risk level, which is considered high when the electrical damping at the TG Torsional Natural Frequencies (TNFs) is negative. Starting from a real case study, a detailed electromechanical model of an LNG plant is presented. The model is comprehensive of the control system of the power conversion stage and of the TG unit. Sensitivity analysis, performed on control system parameters, allows one to detect the parameters that impact the electrical damping and the stability of the overall LNG plant. A complete simulation platform is developed. Experimental results are carried out on a real LNG plant considering four different configurations. The theoretical model and the simulation platform allow one to estimate the electrical damping and the results are confirmed by the experimental validation. It is demonstrated that fine tuning of the power conversion stage control parameters can reduce the risk related to torsional instability.

Networked Fuzzy Control System for a High-Performance Drilling Process

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Rodolfo E. Haber-Guerra ◽  
Rodolfo Haber-Haber ◽  
Diego Martín Andrés ◽  
Angel Alique Palomar
Keyword(s):  
Control System ◽  
Fuzzy Control ◽  
Feed Rate ◽  
High Performance ◽  
Fuzzy Controller ◽  
Reference Signal ◽  
Drilling Process ◽  
Fuzzy Control System ◽  
Optimal Tuning ◽  
Design And Implementation

The high-performance drilling (HPD) process has a significant impact on production in many industries, such as the automotive, die/mold and aerospace industries. However, cutting conditions for drilling are generally chosen from a machining-data handbook, requiring operator experience and skill. In order to improve drilling efficiency while preserving tool life, the current study focuses on the design and implementation of a simple, optimal fuzzy-control system for drilling force. The main topic of this study is the design and implementation of a networked fuzzy controller. The control system consists of a two-input (force error and change of error), single-output (feed-rate increment) fuzzy controller with nine control rules, the sup-product compositional operator for the compositional rule of inference, and the center of area as the defuzzification method. The control algorithm is connected to the process through a multipoint interface (MPI) bus, a proprietary programming, and communication interface for peer-to-peer networking that resembles the PROFIBUS protocol. The output (i.e., feed-rate) signal is transmitted through the MPI; therefore, network-induced delay is unavoidable. The optimal tuning of the fuzzy controller using a maximum known delay is based on the integral time absolute error (ITAE) criterion. The goal is to obtain the optimal tuning parameters for the input scaling factors while minimizing the ITAE performance index. In this study, a step in the force reference signal is considered a disturbance, and the goal is to assess how well the system follows set-point changes using the ITAE criterion. The optimization is performed using the Nelder–Mead simplex (direct search) method. The main advantage of the approach presented herein is the design of a simple fuzzy controller using a known maximum allowable delay to deal with uncertainties and nonlinearities in the drilling process and delays in the network-based application. The results demonstrate that the proposed control strategy provides an excellent transient response without overshoot and a slightly higher drilling time than the CNC working alone (uncontrolled). A major issue in high performance drilling is the increase in cutting force and torque that occurs as the drill depth increases. Therefore, the fuzzy-control system reduces the influence of these factors, thus eliminating the risk of rapid drill wear and catastrophic drill breakage.

Application, Design and Operation Considerations for Brazed Aluminum Heat Exchangers in Liquefied Natural Gas Service

2008 ◽  
Author(s):  
D. Douglas Miller ◽  
Joe A. Belling ◽  
Jane C. Tettambel
Keyword(s):  
Natural Gas ◽  
Heat Exchangers ◽  
Mechanical Design ◽  
Liquefied Natural Gas ◽  
Design Parameters ◽  
Successful Operation ◽  
Design Considerations ◽  
Operational Design ◽  
Design Characteristics ◽  
Lng Liquefaction

Brazed Aluminum Heat Exchangers (BAHX) are commonly used for heat transfer equipment in liquefied natural gas (LNG) services. Specific operational design parameters as well as mechanical design characteristics are critical to consider in the construction and ultimately for the operation of the unit in order to ensure a safe design and successful operation for the facility. The growth and demand for natural gas has been extensive in recent years as clean burning fuels have become more of a priority than coal plants. Due to limited natural gas supplies, many LNG facilities have been considered as a means to provide and meet the consumers’ needs for natural gas. These LNG facilities such as LNG import receiving terminals or LNG Liquefaction Plants have a need for handling cryogenic materials. In these LNG applications, BAHX are an ideal fit for this use and have many advantages as a result of being able to be designed for minimal approach temperatures as well as lower log mean temperature differences (LMTD) than other exchanger types. These parameters are key to the plant’s refrigeration and overall energy loads. Discussed and detailed in this paper will be various uses and applications for BAHX along with design considerations for their use. Details regarding materials of construction, maintenance, and other mechanical aspects will be presented that lead to a safe and reliable means for transferring heat.

Dietary Vitamin and Stability of Oral Anticoagulation: Proposal of a Diet with Constant Vitamin K1 Content

1997 ◽  
Vol 77 (03) ◽  
pp. 504-509 ◽  
Author(s):  
Sarah L Booth ◽  
Jacqueline M Charnley ◽  
James A Sadowski ◽  
Edward Saltzman ◽  
Edwin G Bovill ◽  
...  
Keyword(s):  
Dietary Intake ◽  
Vitamin K ◽  
High Performance ◽  
Case Reports ◽  
Food Composition ◽  
Dietary Guidelines ◽  
Dietary Vitamin ◽  
Vitamin K1 ◽  
The Stability ◽  
The Impact

SummaryCase reports cited in Medline or Biological Abstracts (1966-1996) were reviewed to evaluate the impact of vitamin K1 dietary intake on the stability of anticoagulant control in patients using coumarin derivatives. Reported nutrient-drug interactions cannot always be explained by the vitamin K1 content of the food items. However, metabolic data indicate that a consistent dietary intake of vitamin K is important to attain a daily equilibrium in vitamin K status. We report a diet that provides a stable intake of vitamin K1, equivalent to the current U.S. Recommended Dietary Allowance, using food composition data derived from high-performance liquid chromatography. Inconsistencies in the published literature indicate that prospective clinical studies should be undertaken to clarify the putative dietary vitamin K1-coumarin interaction. The dietary guidelines reported here may be used in such studies.

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