WP1: Connection of offshore wind power to DC grids

This Work Package is led by UPC and has researchers 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.

Research by Kevin (ESR6, Alstom) is currently focussing on T1.6: Wind turbine generation model and T1.7: Wind farm modelling. Aggregated modelling of large-scale wind farm for dynamic simulations will contribute to WP1 milestone M1.4: Wind farm model available for use. Harmonization of secondments in order to increase collaboration within the work package: Kevin and Raza (ESR4, UPC) will go jointly to DTU in 2016, Marc Cheah (ESR2, CU) will be in Cardiff when Kevin is on secondment there

Research by Raza encompasses the following overall targets of the WP1:

• T1.1: Design of DC grid configuration
• T1.8: Control system design
• T1.9: AC fault response

The key achievements includes VSC control system architecture design, development of VSC controller for multi-infeed configuration, and method of determining controller gains to achieved desired response while maintaining system stability.

Inputs from WP2 “Investigation of voltage source converters” is useful to understand requirements and behaviour of HVDC converter for offshore wind power plants for WP1 especially the contributions and models of MMC. Abel Ferreira is involved in WP2, where he is developing  tasks in collaboration with the researchers of WP1. These tasks include:

–           Study the active and reactive power flow exchange of a MMC and the AC grid.

–           Development of a Mathematical Model of a Modular Multilevel Converter- Half Bridge Topology

–          Development of a Power Systems Model of a Modular Multilevel Converter Half Bridge Topology

WP2 Investigation of voltage source converters for DC grids

Cardiff leads this work package and WP members are Cinergia, Universidade do Porto, KU Leuven and CEPRI.

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 will work under the WP2. The 3 ESRs have been recruited. They are

Jorge Goncalves (ESR1 Cardiff), whose individual project is Operation of DC grids with various types of voltage source converter;  Abel Ferreira (ESR5 Cinergia), whose individual project is Power converter design and control for multiterminal DC grids; and Robert Renner (ESR9 KULeuven), whose individual project is Design and implementation of VSC for DC grid.  ER3, Dr. Agustí Egea-Àlvarez has been recruited by CEPRI, and will start from March 2015.

This WP has carried out research on the modelling of two-level, half bridge multi-level, and full bridge multi-level, which include

• 2-Level VSC Simulation Model in PSCAD, achieved in December 2013, corresponds to the Tasks T2.1, T2.4, T2.7, T2.8, and the achievement of the Milestone 2.1. This contributes to the Deliverables D2.1 and D2.6.
• Operation of 2-level VSC’s in a multi-terminal configuration with master/slave and droop control, achieved in December 2013, corresponds to the Tasks T2.7 and T2.8, and contributing to the Milestone M2.5 and Deliverable D2.6.
• Half-bridge MMC Simulation Model: Finished in May 2014, allowing the anticipation of Milestones M2.1 and M2.5 defined in the Research Plan. This Milestone comprises the completion of Tasks T2.1 and T2.4 and culminates in the Deliverables D2.1/D2.6. This was concluded within the initial PCDP timeline.
• H-bridge MMC Simulation Model: Finished in the end of July 2014. This part of the project comprises Tasks T2.1 and T2.4, concluding with Milestones M2,1 and M2.5 and Deliverables D2.1 and D2.6 and was complete ahead of schedule in the PCDP.
• IGBT models, MMC models, modulation strategies, balancing control, harmonic analysis have been developed which cover T2.1, T2.2, and T2.7.
• DC voltage control, restoration and ancillary services of DC grids have been investigated, which cover T2.5-8, M2.2-4, and D2.2-6.

Jorge Goncalves (ESR1) is currently working on the thermal response of MMC under fault conditions. Simulation models have been built and an experimental test system is being design with a target to cover T2.9.

Abel Ferreira (ESR5) is investigating the development of MMC state-of-the-art. This part focuses more on the converter level and operation of MMC.

Robert Renner (ESR9) is working on the literature study of the interaction of AC and DC systems. This part focuses on the system level and operation of MMC. This contributes to WP4 as well.

Jorge Goncalves (ESR3) is working with Marc Cheah (ESR2) of WP1 and Gen Li (ESR12) of WP4 at the Cardiff University on use of MMC for offshore control and main AC grid interaction.  Robert Renner (ESR9) is working more closely with Alejandro (ESR10) in WP4 on the simulation of VSC for power system operation.

Overall progress is very good. One more task T2.3 is to be covered. This can be achieved with collaboration within this WP and with researchers of WP4.

WP3 Relaying Protection

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

Researchers are: ESR7 (Mohammed Meraj Alam, UPORTO) and ESR8 (Ataollah Mokhberdoran, EFACEC), ER2 (Rodrigo Teixeira-Pinto, UPC) and ER5 (Sahar Pirooz-Azad, KU Leuven).

In order to meet T3.1, ERS8 has been working and determined specifications of DC circuit breakers (D3.1) and DC protection requirements (M3.1). Currently ESR8 is at the stage of conducting simulations of the DC circuit breaker, using the SABER software with Simulink from Matlab. ESR8 is expected to start the simulations with the DC Circuit Breaker Prototype early next year after ESR8 return from his secondment.

With regards to Task 3.5, it is being investigated by ESR7. ERS7 has successfully identified impact of DC Grid on AC protection (D3.5); specifically how the impact in a step distance relay performs when the short circuit ratio is been mildly modified from the traditional big inertia AC Generators to the expected newly HVDC links. In addition to ESR7 has designed a HVDC based VSC to assess the current AC protection(T3.5). Up to the day this report is composed, ESR7 has been able to identify the differences and is drawing conclusions on what the differences are and how much impact they would have in the current protection schemes. For the next stage, ERS7 will design and test, based on the arrangements onto the RTDS, a commercial distance relay in a closed loop test. It is expected that by early 2015, with the help from the RTDS simulator and the commercial distance relay, ERS7 will advance the new AC protection scheme which accommodates offshore wind power through DC Grid.

WP3 had recently received ER5, who will start working to achieve T3.3. At the moment, ER5 is investigating possible protection algorithms suitable for DC grids at Katholieke Universiteit Leuven (D3.3) and ER5 will join EFACEC in due time.

More interactions and close communications with other WPs will occur once ER5 from KULeuven joins EFACEC on secondment. As a result, frequent discussions between Prof Dirk Van Hertem and I concerning the algorithm to detect and restore faulted DC grids are expected. As for ER2, Rodrigo Teixeira Pinto from Universitat Politècnica de Catalunya currently is recruiting; this will also pose as an opportunity to discuss with Oriol Gomis about AC and DC power system flow and power system post fault restoration.

WP4 Relaying Protection

WPs is led by KU Leuven and has members based at Cardiff, ELIA and DTU. ESR9 (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.

* There are 2 journal papers submitted for review, and 5 conference papers

* The outreach activities run as planned

* First Secondments are starting

ER4 is scheduled to start work in early 2015.

The following tasks, milestones and deliverables are currently pursued (a number of them will be achieved in the form of a publication when published) :

T4.1, T4.2, T4.3, T4.4, T4.7, T4.8, T4.9

M4.1, M4.2, M4.3, M4.6

D4.1, D4.3, D4.4, D4.5, D4.6,

Close relation with WP2 ESR9 who works on the interface between WP2 and WP4.

This has resulted in a paper submitted (and in the final review phase) to IET journal Generation, Transmission and Distribution on “ancillary services in HVDC grids” (related to T4.5 and T4.6, M4.3 and D4.4. and 4.5

Interaction with the ESRs of WP1 has started.

It is expected that the start of various secondments (outgoing and incomming from WP4 point of view) are expected in the next year.

We are working on a common deliverable by all involved ESRs on HVDC grid codes (expected winter 2015) (D4.4 and D4.5)