December 2015

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.

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 tasks

  • Design of DC grid configuration – completed
  • Economical/technical comparison – in progress
  • Converter characteristics – completed
  • Operating point determination – completed c
  • Steady state power flow programming – completed
  • Wind turbine generation model – in progress (some relevants parts completed)
  • Wind farm modelling – in progress (some relevants parts completed)
  • Control system design – completed
  • AC fault response – in progress
  • Wind power reduction technology – in progress (some relevants parts completed)

WP1 milestones

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

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 – in progress

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.

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.

3 ESRs and 1 ER are working under the WP2.

Jorge Goncalves (ESR1 Cardiff): his 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): his 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): his 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): his individual project is Power flow control devices in DC grids. He joined CEPRI in March 2015 and has proposed a controller to operate the DCDC converter without communications, where the power can be reduced in case of an electrical contingency. He has also suggested a method to avoid the oscillation propagation within the two converter sides.

By reviewing the progress against the tasks, milestones and deliverables set in the Annex 1, some gaps have been identified, such as T2.3 and T2.4, 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 tasks

  • Modelling of two-level, half bridge multi-level, and full bridge multi-level – completed
  • Economic/technical comparison – to be addressed at the appropriate point
  • Monopolar and bipolar transmission – to be addressed at the appropriate point
  • Modelling and function of power control devices – completed
  • Voltage standard – completed
  • VSC connection standard – completed
  • Modelling of converters and other components in DC grids – completed
  • Test the configuration using simulation tools and RTDS – completed
  • Test the configuration using experimental test rig – in progress

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 – to be addressed at the appropriate point
  • 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 – to be addressed at the appropriate point
  • 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 finsihed their time in MEDOW in September 2015.

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

During this period of time, Ataollah Mokhberdoran has designed the 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. He has also assessed the advanced innovative DC circuit breaker with different types, performed locations and resistance faults to understand the behaviour of DC circuit breaker and VSC inverter, as well as impacts on rectified. Promising results were achieved and disseminated in international conferences (EPE2015, Enercon2016), and submission to peer-reviewed journals in the area of investigation and industry transferable knowledge is planned. A patent application was filed on DC circuit breaker during the time this report refers to. Task 3.1 and 3.2 along with milestones 3.1 and 3.2 were already achieved. Ataollah now moves to the stage of prototyping.

Mohammad Meraj is working towards a comprehensive understanding of the influence on the overall power system protection when energy is substituted from conventional big inertia generators to VSC based HVDC (T3.5).

During this period of time, both ER2 and ER5 have finished their research in MEDOW. ER2 focused his attention on the power system restoration plans and security constraint optimal power flow algorithms for DC Grids embedded in AC networks. He has achieved M3.4 as well as completed T3.4 with a developed and validated mixed integer non-linear optimisation algorithm. This algorithm would find actions and equipment set-points during the restoration after a partial or complete blackout when a DC network is embedded in an existing AC network. ER5 developed relaying protection algorithm and achieved T3.3. He has also investigated possible protection algorithms suitable for DC grids and achieved D3.3.

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 tasks

  • Development of simulation platform of DC/AC grids – completed
  • Development of real-time simulation for DC/AC grids – completed
  • Impact of AC faults to DC grids Flexible power flow control – completed
  • Impact of DC faults to AC grid – in progress
  • Investigation of DC grid code – completed
  • Investigation of AC grid code with DC grids – in progress
  • Support of DC grids to AC stability – completed
  • Damping of SSR using DC grids – completed
  • Test transmission and control of wind power to AC grids through DC grids in simulation software package – completed
  • Validate the transmission and control system using RTDS – completed
  • Validate the DC grid operation using experimental test rig – completed

WP4 milestones

  • Impact between AC and DC grids determined – in progress
  • Recommendation of DC grid code made – completed
  • suggestion on AC grid code made – in progress
  • Control strategy to remove the obstacle for DC/AC interconnection designed – in progress
  • AC/DC system and control strategy validated – completed
  • Simulation platforms available for use – completed
  • Test rig available for investigating DC/AC grids – 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
  • Determination of the impact of DC faults on AC grids – completed
  • Recommendation of DC grid code to be met by any new terminal
  • 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 – completed
  • Coordinated control strategies of multi-terminal DC grids for ancillary services delivered by wind power plants – completed