Coordinated control strategies to provide system inertia support for main grid from offshore wind farm that is integrated through HVdc transmission is the subject matter of this paper. The strategy that seeks to provide inertia support to the main grid through simultaneous utilization of HVdc capacitors energy, and wind turbines (WTs) inertia without installing the remote communication of two HVdc terminals is introduced in details. Consequently, a novel strategy is proposed to improve system inertia through sequentially exerting dc capacitors energy and then WTs inertia via a cascading control scheme. Both strategies can effectively provide inertia support while the second one minimizes the control impacts on harvesting wind energy with the aid of communication between onshore and offshore ac grids. Case studies of a wind farm connecting with a HVdc system considering sudden load variations have been successfully conducted to compare and demonstrate the effectiveness of the control strategies in DIgSILENT/PowerFactory.

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Coordinated Control Strategies for Offshore Wind Farm Integration via VSC-HVDC for System Frequency Support

This paper analyzes the frequency support characteristics of multiterminal voltage source converter HVdc (VSC–HVdc) (MTDC) schemes using the energy transferred from wind turbine rotating mass and other ac systems. An alternative coordinated control (ACC) scheme that gives priority to a frequency versus active power droop fitted to onshore VSCs is proposed to: transfer wind turbine recovery power to undisturbed ac grids, and allow correct control operation of MTDC systems during multiple power imbalances on different ac grids. The fast frequency response capability of MTDC systems equipped with the proposed ACC scheme is compared against a coordinated control scheme, which uses a frequency versus dc voltage droop. The frequency control schemes are demonstrated on an experimental test rig, which represents a three-terminal HVdc system. Also, the MTDC frequency support capability when wind farms do not provide extra power is tested using a four-terminal HVdc system.

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Fast Frequency Response From Offshore Multiterminal VSC–HVDC Schemes

http://webx.ubi.pt/~catalao/IJEPES-D-14-00473R1_Paper.pdf

Frequency regulation in hybrid power systems using particle swarm optimization and linear matrix inequalities based robust controller design

A two-stage scheduling optimization model and solution algorithm for wind power and energy storage system considering uncertainty and demand response

The continuous displacement of conventional power plants by converter-interfaced generation systems reduces the system inertia and may lead to a degradation of the frequency stabili-leon-2757258ty A supplementary control strategy for multi-terminal dc (MTDC) systems to improve the frequency regulation is presented in this paper The scenario where the MTDC system cannot resort to the power reserves of either other ac systems or offshore wind farms is particularly studied The proposed control is able to independently support both the primary frequency regulation and the system inertia by using the capacitive energy of the MTDC grid converters On the other hand, the reactive power of the converter stations is coordinately controlled to improve the damping of low-frequency electromechanical oscillations The simultaneous frequency support of the MTDC system and onshore wind farms is also studied and validated in a practical multi-machine power system Transient and small-signal stability analyses are performed to evaluate and quantify the improvements and the control limitations of the proposed scheme This enhanced frequency control can increase the system reliability and reduce the required amount of spinning reserve, diminishing the operation costs and allowing to increase the penetration of renewable energy sources

Yong Yang

Papers

Coordinated control of wind farm and VSC–HVDC system using capacitor energy and kinetic energy to improve inertia level of power systems