Dynamics and Stability of Meshed Multiterminal HVDC Networks

Abstract

This paper investigates the existence of an equilibrium point in multiterminal HVDC (MT-HVDC) grids, assesses its uniqueness and defines conditions to ensure its stability. An offshore MT-HVDC system including two wind farms is selected as application test case. At first, a generalized dynamic model of the network is proposed, using hypergraph theory. Such model captures the frequency dependence of transmission lines and cables, it is non-linear due to the constant power behavior of the converter terminals using droop regulation, and presents a suitable degree of simplifications of the MMC converters, under given conditions, to allow system level studies over potentially large networks. Based on this model, the existence and uniqueness of the equilibrium point is demonstrated by returning the analysis to a load-flow problem and using the Banach fixed point theorem. Additionally, the stability of the equilibrium is analyzed by obtaining a Lyapunov function by the Krasovskiis theorem. Computational results obtained for the selected 4 terminal MT-HVDC grid corroborate the requirement for the existence and stability of the equilibrium point.Index Terms-Offshore wind energy, Multiterminal HVDC systems, HVDC, transient stability, equilibrium point, dynamic systems.

Multi-Terminal HVDC System With Offshore Wind Farms Under Anomalous Conditions: Stability Assessment

“…In this paper, the two-level VSC is assumed to simplify the simulation model for such a large system. However, in converters such as MMCs, the dynamics of the internal state variables can be neglected assuming well-regulated MMC, where the order of the MMC model can be reduced to first-order similar to that in [30]. The time constant of this reduced-order model can be assumed small (namely, the current control loop); hence the presented concept can be employed.…”

Contraction Analysis for a MMC Converter

“…Different approaches to the model of the MMC have been made, for the purpose of this paper, we will take as reference the development in [9] and [10]. It is a common procedure in power systems analysis to approximate the fast transient behaviour of the power electronics converter to an active power injection model as presented in [1]. This approximation is based on the reasonable assumption that the converters are tightly-regulated, the harmonic distortion is negligible, DC faults are outside the scope of the analysis, the transient response is typically in the range of few milliseconds, losses can be neglected and a generic model can be used to represent the dynamics.…”

“…T HE increasing penetration of renewable energy in the traditional power system and particularly the massive integration of offshore wind farms has created the need to generate new control and analysis strategies in the Power systems. The use of the Voltage Source Converter (VSC) technology, with independent control of active and reactive power at the AC terminals is considered and advantage to support weak power systems [1]. Classic stability analysis in power systems requires three main steps: modelling, load flow calculation and dynamic analysis.…”

Impact of the Wind Turbine on the Parameters of the Electricity Supply to an Agricultural Farm

“…Many authors have also addressed power plant grid cooperation [31][32][33][34][35]. Some of them dealt with the dynamic impact of power plants [36,37]. However, none of the items dealt with analyzing the impact of a power plant on loads installed in its immediate vicinity.…”