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

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.

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

Energies ◽

10.3390/en13102612 ◽

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.

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Liquefied natural gas submerged combustion vaporization facilities: process integration with power conversion units

International Journal of Energy Research ◽

10.1002/er.1937 ◽

2011 ◽

Vol 37 (1) ◽

pp. 80-92 ◽

Cited By ~ 13

Author(s):

Giulio Tagliafico ◽

Federico Valsuani ◽

Luca A. Tagliafico

Keyword(s):

Natural Gas ◽

Process Integration ◽

Power Conversion ◽

Liquefied Natural Gas ◽

Submerged Combustion

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

Energies ◽

10.3390/en14175238 ◽

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.

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