Please see our Dissemination webpages for details of researcher publications.

WP1: Connection of offshore wind power to DC grids

This Work Package is led by UPC and has researchers, Marc Cheah, Muhammad Raza, Kevin Schönleber and Domenico Ricchiuto, based in Cardiff, UPC and ALSTOM (GE).  Domenico completed his time in MEDOW in March.

The WP is advancing as expected and we are making progress on our objectives:

O1: Design and analyse the topologies of offshore DC grids. Some work has been done in the direction of designing, analysing and controlling offshore AC hubs comprising several wind farms and power converters. Next steps will include multiterminal HVDC systems and offshore HVDC grids.

O2: Determine steady state operation characteristics. The power converter operation characteristics have been identified and algorithms for analysis have been developed.

O3: Develop dynamic control systems for offshore DC grids. Appropriate models have been developed to analyse the dynamic behaviours of offshore AC hubs with offshore wind power plants.

WP1 milestones

• DC grids suitable for offshore wind determined – partially achieved
• Converter characteristics determined – achieved
• Algorithms for determining operating points developed – achieved
• Wind farm model available for use – partially achieved
• Wind power reduction method developed – partially achieved

WP1 Deliverables

• Various DC grid configuration; cost model technical index and comparison algorithm – deliverable pending, most of the work done
• Various operation modes of converters, V-I characteristics – deliverable pending, most of the work done
• Methods for determining the operating points – deliverable pending, most of the work done
• Controllers of wind farm converters of the DC grid – deliverable pending, important part of the work done
• Methods to reduce wind power output to avoid over DC voltage – deliverable pending, important part of the work done

WP2 Investigation of voltage source converters for DC grids

Cardiff leads this work package and WP members are Cinergia, KU Leuven and CEPRI, represented by researchers Jorge Gonçalves, Abel Ferreira, Robert Renner and Agustí Egea.  Agustí completed his MEDOW contract this month.

The main research objectives of the WP2 is to investigate the interaction of various voltage source converters (two level, half bridge MMC (modular multi-level converter), full bride MMC and mixed MCC) operating in the same DC grids.

Jorge Goncalves (ESR1 Cardiff), whose individual project is Operation of DC grids with various types of voltage source converters. The 2-Level and Half-Bridge and Full-Bridge MMC converter models have been developed and validated in different software platforms. He has recently finished the assembly of an experimental platform and is on the process of validation of several control methods, targeting the cover of T2.9 and M2.5.

Abel Ferreira (ESR5 Cinergia), whose individual project is Power converter design and control for multiterminal DC grids. He investigates various types of MMC. Experimental tests are carried out using facilities of Cinergia.

Robert Renner (ESR9 KULeuven), whose individual project is Design and implementation of VSC for DC grid. His work has covered many tasks of WP2 on MMC and WP4 on ancillary service of AC systems. Very good results have been achieved.

Dr. Agustí Egea-Àlvarez (ER3 CEPRI), whose individual project is Power flow control devices in DC grids. He has completed his work at CEPRI successfully on 15th March 2016 and taken a new job in Glasgow UK.

By reviewing the progress against the tasks, milestones and deliverables set in the Annex 1, some gaps have been identified, such as T2.2 and T2.3, M2.4 and D2.2 on economic models and analysis of converters, and test of grid configurations. Considering that there is still some time until the end of their PhD studies, efforts will be identified to cover these gaps and proper methods will be used.

WP2 milestones

• Model of voltage source converter developed – completed
• Identification of the problem in various configurations and solutions provided – completed
• Recommendation on the DC grid standardisation – completed
• DC grid configuration tested – in progress
• Simulation software packages and experimental test platform available for use – completed

WP2 deliverables

• Models of two-level and multi-level converters for simulation – completed
• Cost model technical index and comparison algorithm – in progress
• Configurations of converter stations; configurations of DC grid with combination of different types of converters – in progress
• Suggestions on the DC voltage levels – completed
• Recommendation on the standard for connecting more converters – completed
• Simulation models of converters, cables, grounding and DC network – completed

WP3 Relaying Protection

Universidade do Porto leads this work package and WP members are EFACEC, UPC and KU Leuven.

Researchers are: Mohammed Meraj Alam (UPORTO), Ataollah Mokhberdoran (EFACEC), Rodrigo Teixeira-Pinto (UPC) and Sahar Pirooz-Azad (KU Leuven).  Rodrigo and Sahar finished their time in MEDOW in September 2015.

This report relates the main activities of P3 from October 2015 to the end of February 2016.

During this period of time, Ataollah Mokhberdoran has continued assessing his advanced so-called Ultra-Fast Solid-State DC Circuit Breaker, given that the breaking current capability and fault clearance time required for the DC circuit breaker is specified.  ESR8 has assessed the DC circuit breaker on the software SABER, Simulink, PSim, Orcad. Results has been disseminated in international conferences and submission to peer-reviewed journals in the area of investigation and industry transferable knowledge is planned in the short-term.  ERS8 is ready for hands-on prototyping of the DC circuit breaker. Task 3.1 and 3.2 along with milestones 3.1, 3.2 were already achieved and disseminated.  Milestone M3.4 is on its way to be completed in the next semester.

Mohammad Meraj Alam has modelled the VSC based HVDC onto RTDS simulator and is preparing closed-loop test with RTDS simulator, power amplifier and a commercial distance relay from EFACEC.  The impact of a VSC based HVDC the actual AC Power System Protection can be advanced with this closed-loop test.  Although the test rig is not yet completed progress has been made.

WP3 milestones

• DC protection requirement determined – completed
• DC circuit breaker technologies summarised – completed
• DC protection algorithm developed – completed
• Post-fault restoration with various DC circuit breakers and isolators determined – in progress
• Solution of AC protection upgrade provided – in progress

WP3 deliverables

• Determined specification of DC circuit breakers to meet DC fault handling requirements – completed
• Test circuit for DC protection available – completed
• Protection algorithm suitable for DC grids – completed
• Procedures to clear the DC faults and restore the DC grid – in progress
• Impact of DC grid to AC protection – completed
• Solution to reduce the impact of AC protection – in progress

WP4 Relaying Protection

WP4 is led by KU Leuven and has members based at Cardiff, ELIA, DTU and Cardiff: Tibin Joseph, Gen Li, Alejandro Bayo Salas, Jayachandra Naidu and Qing Mu. ESR9 Robert Renner of WP2 also contributes to the Work package.

All ESRs are now working towards their goals, first results are being delivered. Also the first publications are realized.

WP4 milestones

• Impact between AC and DC grids determined – completed
• Recommendation of DC grid code made – completed
• suggestion on AC grid code made – completed
• Control strategy to remove the obstacle for DC/AC interconnection designed – completed
• AC/DC system and control strategy validated – partially completed
• Simulation platforms available for use – completed
• Test rig available for investigating DC/AC grids – partially completed

WP4 deliverables

• Integrated AC/DC grid model developed on various simulation tools – completed
• Power flow algorithm developed; determination of the impact of AC faults on DC grids – in progress
• Determination of the impact of DC faults on AC grids – completed
• Recommendation of DC grid code to be met by any new terminal – in progress
• Suggestion of the AC grid code to connect DC grids – in progress
• Controllers to improve stability of AC grid and to damp the SSR developed – completed
• Validated AC/DC grid models; validated control system – in progress
• Experimental test platform available for use – partially completed
• Coordinated control strategies of multi-terminal DC grids for ancillary services delivered by wind power plants – completed