Modeling and Analyzing the Effect of Frequency Variation on Weak Grid-Connected VSC System Stability in DC Voltage Control Timescale

Yang, Hui; Yuan, Xiaoming

doi:10.3390/en12234458

Cited by 5 publications

(3 citation statements)

References 25 publications

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“…The power conversion stage is taken into account through an average model where only the passive components of the circuits are considered, as in [13,25]. On the contrary, independent of the specific application, small-signal analysis allows us to achieve dynamic models of the power system for fair stability assessment in the case of weak grids [26,27]. In this paper, an ad-hoc state-space dynamic model of a combined electromechanical system is developed.…”

Section: Introductionmentioning

confidence: 99%

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

Bongini

Mastromauro

Sgro³

et al. 2020

Energies

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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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Section: Introductionmentioning

confidence: 99%

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

Bongini

Mastromauro

Sgro³

et al. 2020

Energies

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“…In Reference [13], it is studied the impact of phase-locked loop (PLL) on impedance modeling and resonance in a doubly fed induction generator RES with a parallel compensated weak grid. In Reference [14], a thorough analysis of the effect mechanism of frequency variation on the weak grid-connected VSI system stability in a dc voltage control timescale is presented. In Reference [15], the stability of multiple DERs that are connected in parallel to a weak ac grid is analyzed.…”

Section: Introductionmentioning

confidence: 99%

“…Obviously, Equation 23represents the integrator term of the PI controller (Equation 22), where now the damping term k Ig Z q has been inserted in a common way, as described in Equation (14).…”

mentioning

confidence: 99%

Validation of Novel PLL-driven PI Control Schemes on Supporting VSIs in Weak AC-Connections

2020

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The integration of distributed energy resources (DERs) in modern power systems has substantially changed the local control capabilities of the grid since the majority of DERs are connected through a controlled dc/ac inverter interface. Such long-distance located DER installations, usually represented by current regulated dc sources, can inject large amounts of power into the main ac grid at points where the strength of the ac connection is low. The efficient and stable performance of such a power scheme is related to the capability of the control applied to retain the power extraction close to the maximum and simultaneously to regulate the dc-side voltage as well as the ac-side voltage magnitude at the weak ac connection point. This is implemented by designing the controllers of the voltage source inverters (VSIs) in a manner that reliably satisfies the above tasks. To this end, decentralized cascaded control schemes, driven by novel, locally implemented phase locked loops (PLLs), suitable to work in weak ac connections, are proposed for the VSI performance regulation by using new fast inner-loop proportional-integral (PI) current controllers. A decisive innovation is proposed by inserting an extra damping term in the inner-loop controllers to guarantee stability and convergence to the desired equilibrium. This is analytically proven by a rigorous analysis based on the entire nonlinear system model, where advanced Lyapunov-based methods are deployed in detail. As a good transient response of the VSI interface is indeed critical for the energy and grid system management, the conducted simulation and experimental results confirm that the proposed scheme efficiently supports the ac- and dc-side voltages of the VSI under different varying conditions in the power production or any voltage changes of the main grid.

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Dynamic Network Characteristics of Power-electronics-based Power Systems

Cheng

et al. 2020

Sci Rep

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Power flow studies in traditional power systems aim to uncover the stationary relationship between voltage amplitude and phase and active and reactive powers; they are important for both stationary and dynamic power system analysis. With the increasing penetration of large-scale power electronics devices including renewable generations interfaced with converters, the power systems become gradually power-electronics-dominant and correspondingly their dynamical behavior changes substantially. Due to the fast dynamics of converters, such as AC current controller, the quasi-stationary state approximation, which has been widely used in power systems, is no longer appropriate and should be reexamined. In this paper, for a better description of network characteristics, we develop a novel concept of dynamic power flow and uncover an explicit dynamic relation between the instantaneous powers and the voltage vectors. This mathematical relation has been well verified by simulations on transient analysis of a small power-electronics-based power system, and a small-signal frequency-domain stability analysis of a voltage source converter connected to an infinitely strong bus. These results demonstrate the applicability of the proposed method and shed an improved light on our understanding of power-electronics-dominant power systems, whose dynamical nature remains obscure.

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Modeling and Analyzing the Effect of Frequency Variation on Weak Grid-Connected VSC System Stability in DC Voltage Control Timescale

Cited by 5 publications

References 25 publications

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

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

Validation of Novel PLL-driven PI Control Schemes on Supporting VSIs in Weak AC-Connections

Dynamic Network Characteristics of Power-electronics-based Power Systems

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