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.
We are starting with the work of the different ESRs:
– ESR2 Optimal wind power transfer through DC grid CU
– ESR4 Control of multi-terminal HVDC systems for offshore wind power UPC
– ESR6 Control of wind farms interfaced to multiterminal DC systems ALSTOM Wind
The main achievement has been to recruit the researchers and to have all of them in post.
The objectives for the overall project duration have been confirmed as:
O1: Design and analyse the topologies of offshore DC grids
O2: Determine steady state operation characteristics
O3: Develop dynamic control systems for offshore DC grids
The ESRs are working on the design of a common platform for future studies. It expected to increase the interaction in the next year.
In the frame of this work package was organized, in cooperation with KIC InnoEnergy education branch, the Workshop “HVDC TOWARDS THE FUTURE”.
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 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 be working under the WP2. The 3 ESRs have been recruited:
– Jorge Goncalves (ESR3 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.
An ER (ER3) will be recruited by CEPRI in 2014.
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
• Operation of 2-level VSC’s in a multi-terminal configuration with master/slave and droop control
• Half-bridge MMC Simulation Model
• H-bridge MMC Simulation Model
Jorge Goncalves (ESR3) is currently working on the thermal response of MMC under fault conditions. Capacity of converters can be fully used by dynamically setting current limits and considering device temperatures.
Abel Ferreira (ESR5) is investigating the development of MMC state-of-the-art.
Robert Renner (ESR9) is working on a literature study of the interaction of AC and DC systems.
WP3 Relaying Protection
Universidade do Porto leads this work package and WP members are EFACEC, UPC and KU Leuven.
ESR7 (Mohammed Meraj Alam) and ESR8 (Ataollah Mokhberdoran) are already in post and will be joined by ER2 (UPC) and ER5 (KU Leuven) later in 2014.
ESR7 has carried out work on the impact of distance protection due to interconnection of offshore wind HVDC network through VSC and on under-reach as well as over-reach of distance relay in an IEEE 39 bus system with an integrated VSC. he has studied possible systems having a VSC, operating with constant DC voltage control, under power swing, independent P & Q control and with fault resistance. A two generator system connected by a long transmission line has been studied in order to determine the reach of step distance relay for three zones of protection in PSCAD.
ESR8 has been working on a study of dynamical behaviour of IGBT transistors as key elements for designing DCCBs. Within this framework, he has started to use SABER software as the desired design tool. He has also carried out studies of the fundamentals of further research, characteristics and development stages of DC fault currents and key approaches for the design of semiconductor based DC circuit breakers series and parallel connection of IGBT chips and IGBT modules. Also, gate driving technologies and auxiliary circuits for protection of semiconductor devices during interruption of high currents under high voltages have been explored.
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.
Tibin Joseph (ESR3) has worked on the IEEE First Bench Mark model for Sub synchronous studies (SSR) studies, developed the model in PSCAD and has also detailed state space representation in MATLAB environment for performing the Eigen value analysis in order to analyse the stability of the system under different operating conditions and also to investigate the effect of the series compensation on system stability.
He has modelled a three machine Great Britain (GB) network and modified that with series compensation and also with a point to point VSC HVDC system for AC/DC interaction studies and performed simulations and SSR studies in PSCAD. Time domain simulation for various levels of series compensation and the effect of DC grid control on the SSR developed have been analysed. A supplementary control has been implemented for damping the SSR developed along with the primary control of the DC grid converter controls and the time domain simulation of the proposed control system has been verified. Tibin has also modelled AC/MTDC system in collaboration with ESR 12 and the effects of SSR on this system is currently under investigation.
Gen Li (ESR12) has studied the principles of VSC HVDC and completed several simulation models in PSCAD/EMTDC. The models are different VSC converter configurations, MTDC grids, multi-machine AC systems and integrated AC-MTDC systems. With these models, the analysis of the impacts of DC faults on AC systems, interactions between AC and DC systems, the overall stability of AC-MTDC system, and damping SSR in GB transmission network with MTDC grid were studied. Gen has recently been studying the modeling of MMC (reduced model) and trying to use the multi-terminal test rig and RTDS in the Cardiff labs.
Jayachandra Naidu (ESR11) joined the network in Spring 2014 and, in addition to preparing his PhD study plan and MEDOW PCDP and attending a variety of PhD training courses, he has carried out a literature review (state of the art) on ancillary services from wind power plants, DC Grid Control. He has also received training at DTU on DIgSILIENT Power Factory tool, which will be used for project simulations.
Alejandro Bayo Salas (ESR10) has carried out studies of modelling and stability assessment of VSCs. A model with the linearized state-space equations of the VSC was developed in the software Simulink. Two models of an averaged and switched VSC were built in PSCAD for validation purposes. Currently, different models of the input-admittance of a VSC considering different reductions are being obtained. With these, he is studying the impact of the AC system strength on the operation of the VSC.