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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Storage & grid integration' taking place on Wednesday, 12 March 2014 at 16:30 -18:00. The meet-the-authors will take place in the poster area.

Ahmed Moawwad Masdar Institute of Science and Technology, United Arab Emirates
Co-authors:
Ahmed Moawwad (1) F P
(1) Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

received the B.Sc. degree in Electrical Power and Machines Engineering from Ain Shams University, Cairo, Egypt, in 2008 and the M.Sc. degree from Masdar Institute of Science and Technology, Abu Dhabi, UAE, in 2012. He is currently pursuing his PhD. degree at Masdar Institute. He was with ABB Power Systems and Automation Technologies, Egypt for two years from 2008, where he worked as control system engineer for power generation plants.
His research interests include power system voltage control, applications of power electronics in renewable energy, HVDC and FACTS devices.

Abstract

FRT enhancement for VSC-HVDC interconnected PMSG offshore wind power plants

Introduction

During the last decades, Wind Energy Conversion System (WECS) has grown dramatically. Thus, there will be plenty of power electronic VSCs in a WPP—right from the FSCs in the WTGs to the VSC-HVDC. The current control capability of these converters can be utilized to control the negative sequence current injection in the offshore WPP grid during unbalanced operating conditions arising out of asymmetric faults. Some references presented the control of WTG-GSC during unbalanced grid conditions. The appearance of second harmonic oscillations in power flow and the need for power reduction during unbalanced grid conditions have been highlighted.

Approach

This paper investigates the dynamic behavior of an offshore Wind Power Plant (WPP) based on Permanent Magnet Synchronous Generator (PMSG) connected through VSC-HVDC. Models and equations that describe different components of the PMSG are addressed and implemented. A detailed model for the VSC-HVDC is implemented and its controllers are developed. The offshore VSC station controller is based on positive sequence controller only, while the onshore VSC station is based on positive and negative sequence controllers. The negative sequence controller is used to mitigate the oscillatory power components and the corresponding DC voltage ripples caused by asymmetrical faults.

Main body of abstract

The main components of the gearless variable-speed WECS are the wind-turbine, the permanent magnet synchronous generator, the back to back converters with their control, and the pitch controller. A 2.0 MW direct drive WT unit is considered for this analysis. The components used in the models:
1) Wind turbine
The turbine model is based on the steady-state power characteristics of the turbine. The friction factor and the inertia of the turbine are combined with those of the generator coupled to the turbine.
2) The permanent magnet synchronous generator
A third order model is used to represent the PMSG on PSCAD/EMTDC software package. The mathematical model is described in more details in the full paper.
3) The back to back converters
The back to back converters, are used to connect the PMSG to the internal WPP grid. The main function of the grid-side converter is to regulate the dc link voltage at a constant value. On the other hand, the machine side converter is used to extract the maximum power from the wind turbine and to regulate the rotational speed.
VSC-HVDC System:
The conventional control approach of the off-shore and onshore shunt connection has a nested-loop structure. It consists of a faster inner current loop and a slower outer control loop. The outer control loop generates the dq axis current references to the current loop controller. Positive and negative sequence components are designed for balanced and unbalanced fault conditions.


Conclusion

The paper presents a detailed model for offshore WPP. The dynamic performance of the machine-side converter and the grid-side converter are investigated. Also a VSC-HVDC is modelled to transmit the active power from the offshore WPP to the electrical grid. Positive and negative sequence controllers are designed for the VSC-HVDC operation during different conditions. The positive sequence controller is used to control the average active powers and reactive support for the PCC voltage during disturbances. The negative sequence currents are controlled in such a way to reduce the power oscillations and the DC link voltage ripples associated with asymmetrical faults.


Learning objectives
1- Explaining the importance of riding different types of faults for the off-shore wind farms.
2- highlighting the role of negative sequence components on the ripples of the DC link voltage.
3- Proposing a mathematical model to mitigate the effect of this negative sequence components on both; DC link voltage and the electrical grid.