Modelling and Dynamic Analysis of a Power System with VSCHVDC Radial Plus Strategy

Abstract

This work presents the analysis of a radial plus VSC-HVDC scheme in terms of its impact on AC and DC system dynamics. This study uses the classical two-area system with modified demand as an onshore AC grid. Full converter wind power plants (WPPs) are connected to the main grid through two point-to-point VSC-HVDC links, which are connected offshore through an AC cable to form a 'radial plus' strategy for VSC-HVDC connection. A variety of different control schemes for the radial plus VSC-HVDC are described and analysed to find out the impact of these controllers on the dynamic behaviour of the system. Simulation results are presented to illustrate the impact of different control combinations on system dynamic performance under various grid disturbances.

The Impact of Voltage Regulation of Multiinfeed VSC-HVDC on Power System Stability

“…To measure the transient voltage stability of the system, a transient voltage severity index (TVSI) proposed in [31] has been used in this paper. Transient voltage performance of the system buses following the clearance of the fault can be evaluated as (12):…”

“…In (12), N refers to the total number of buses in the system, T represents the time-frame considered for evaluating TVSI (4.5 s in this case), T c is the fault clearing time, and TVDI i,t is the transient voltage deviation index of bus i at time t. The TVDI i,t can be evaluated as (13).…”

“…However, little information regarding the impacts of this control scheme on the overall stability of the system is presented. Moreover, the conclusions obtained from embedded links may not be valid under a MI-HVDC scenario since the dynamics of the interacting VSC-HVDC links in a network affect the potential operational parameter ranges of the controllers [11], [12]. Furthermore, the design of a voltage controller in prior cited works is limited by the unknown network parameters and dynamics.…”

Characterisation of interaction in an offshore AC grid with large WPPs and VSC‐HVDCs

“…In 1, 'Δ' represents the small perturbation, Y dd and Y qq correspond to the diagonal elements of dq components, while, Y dq and Y qd correspond to the cross-coupling of dq components. Since the control of the grid-side converter is implemented in the synchronous dq frame, the dynamic equations for a grid-side converter of a full-converter wind generator can be expressed as [15], (b) FF control of offshore VSC-HVDC [1,14], (c) Vector control of offshore VSC-HVDC [18] are the resistance, inductance of the reactor and converter transformer, and ω is the angular frequency of the grid. The voltage references at the switching valve can be expressed as [9,11]…”

“…The growing desire to connect the offshore wind sites in the North Sea and asynchronous grids around the region may eventually result in the formation of multi-terminal DC (MTDC) grids. However, if built, the often proposed MTDC 'SuperGrid' for the North Sea will be pieced together gradually with the most likely first step being based on integrating offshore wind power plants (WPPs) by AC cables to form an offshore AC grid [1]. The operation of offshore voltage-sourced converter high-voltage DC (VSC-HVDC) lines under an AC integrated topology within the offshore AC grid poses some challenges including the stability of the offshore grid.…”