Optimisation of VSC-HVDC Transmission for Wind Power Plants

Research output: Book/ReportPh.D. thesisResearch

Abstract

Connection of Wind Power Plants (WPP), typically oshore, using VSCHVDC transmission is an emerging solution with many benefits compared to the traditional AC solution, especially concerning the impact on control architecture of the wind farms and the grid.

The VSC-HVDC solution is likely to meet more stringent grid codes than a conventional AC transmission connection. The purpose of this project is to analyse how HVDC solution, considering the voltage-source converter based technology, for grid connection of large wind power plants can be designed and optimised. By optimisation, the project aims to study the control of DC grids.

The first part considers the static analysis of the multiterminal DC connection. An optimal design methodology for loss minimisation and one based in the dispatch error minimisation are proposed. The algorithm outputs are the droop factors which are included as most outer controllers in the onshore shore converter stations. With the voltage drops given by the controllers, the schedule dispatch for the DC grid is then dened.

The optimisation technique applied in the definition of the droop factor in the multiterminal control mode presents exibility in meeting the requirements established by the operators in the multiterminal VSC-HVDC transmission system. Moreover, the possibility in minimising the overall transmission losses can be a solution for small grids and the minimisation in the dispatch error is a new solution for power deliver maximisation.

The second study takes into account the dynamics of the system. The converter stability analysis is performed and, from its results, the optimisation criteria used fo the static operation of multiterminal DC systems can be refined. The application of the robust control technique based in -synthesis appears as a contribution to the study of parameter variations in the DC systems. This method is able to simplify the system modelling, considering the range of variations of the system variables instead of the use of a complete dynamic description of interconnected system.

The performance of the system dynamics when the robust control technique is applied is compared with the classical proportional-integral (PI) performance, by means of time domain simulation in a point-to-point HVDC connection. The three main parameters in the discussion are the wind power delivered from the offshore wind power plant, the variation of the DC voltage reference in the onshore converter station and, at the end, the grid equivalent short-circuit ratio
impedance.

Connecting both, the static optimisation and dynamic analysis, the project is a starting point to the quantification of the ability of the system in support standalone operation and/or justify the insertion of high speed communication link whether the robust performance of the system does not meet the requirements established by the partners tied by the HVDC multiterminal link as an example.

The study of the system stability using uncertainty model can simplify the analysis of large networks in order to design the control parameters of voltage source converters. This technique, based in structure singular values and the control design by means of -synthesis, presents as disadvantages the use of higher order controllers. On the other hand, the improvements in the dynamic performance under system variations justify the usage of such approach.
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Connection of Wind Power Plants (WPP), typically oshore, using VSCHVDC transmission is an emerging solution with many benefits compared to the traditional AC solution, especially concerning the impact on control architecture of the wind farms and the grid.

The VSC-HVDC solution is likely to meet more stringent grid codes than a conventional AC transmission connection. The purpose of this project is to analyse how HVDC solution, considering the voltage-source converter based technology, for grid connection of large wind power plants can be designed and optimised. By optimisation, the project aims to study the control of DC grids.

The first part considers the static analysis of the multiterminal DC connection. An optimal design methodology for loss minimisation and one based in the dispatch error minimisation are proposed. The algorithm outputs are the droop factors which are included as most outer controllers in the onshore shore converter stations. With the voltage drops given by the controllers, the schedule dispatch for the DC grid is then dened.

The optimisation technique applied in the definition of the droop factor in the multiterminal control mode presents exibility in meeting the requirements established by the operators in the multiterminal VSC-HVDC transmission system. Moreover, the possibility in minimising the overall transmission losses can be a solution for small grids and the minimisation in the dispatch error is a new solution for power deliver maximisation.

The second study takes into account the dynamics of the system. The converter stability analysis is performed and, from its results, the optimisation criteria used fo the static operation of multiterminal DC systems can be refined. The application of the robust control technique based in -synthesis appears as a contribution to the study of parameter variations in the DC systems. This method is able to simplify the system modelling, considering the range of variations of the system variables instead of the use of a complete dynamic description of interconnected system.

The performance of the system dynamics when the robust control technique is applied is compared with the classical proportional-integral (PI) performance, by means of time domain simulation in a point-to-point HVDC connection. The three main parameters in the discussion are the wind power delivered from the offshore wind power plant, the variation of the DC voltage reference in the onshore converter station and, at the end, the grid equivalent short-circuit ratio
impedance.

Connecting both, the static optimisation and dynamic analysis, the project is a starting point to the quantification of the ability of the system in support standalone operation and/or justify the insertion of high speed communication link whether the robust performance of the system does not meet the requirements established by the partners tied by the HVDC multiterminal link as an example.

The study of the system stability using uncertainty model can simplify the analysis of large networks in order to design the control parameters of voltage source converters. This technique, based in structure singular values and the control design by means of -synthesis, presents as disadvantages the use of higher order controllers. On the other hand, the improvements in the dynamic performance under system variations justify the usage of such approach.
Original languageEnglish
PublisherDepartment of Energy Technology, Aalborg University
Number of pages195
StatePublished - 2012
Publication categoryResearch

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