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National Renewable Energy Centre Chong Ng, Principal Engineer – Reliability & Validation Paul McKeever, R&D Manager OFFSHORE RENEWABLE PLANT HVDC POWER.

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Presentation on theme: "National Renewable Energy Centre Chong Ng, Principal Engineer – Reliability & Validation Paul McKeever, R&D Manager OFFSHORE RENEWABLE PLANT HVDC POWER."— Presentation transcript:

1 National Renewable Energy Centre Chong Ng, Principal Engineer – Reliability & Validation Paul McKeever, R&D Manager OFFSHORE RENEWABLE PLANT HVDC POWER COLLECTOR AND DISTRIBUTOR EWEA 2013 February, 2013, Vienna, Austria

2 Existing 50m blade test Still water tank Wave flume Simulated seabed Wind turbine training tower Electrical and materials laboratories New 3MW tidal turbine drive train - 2012 Offshore anemometry hub - 2012 100m blade test - 2012 15MW wind turbine drive train - 2013 99.9MW offshore wind demonstration site - 2013/14 Narec – Created by Government to stimulate the RE industry, A Controlled and Independent Testing Environment

3 Presentation Contents Technical Paper Background Existing Systems – HVAC transmission systems – HVDC systems Proposed HVDC System Selected Challenges Conclusions Next Steps

4 Technical Paper Background UK requires offshore wind to meet its renewable energy generation targets (2020, 2030, 2050…) – UK Energy Bill … by 2020, 30% from Renewable Energy Likely to involve larger turbines (10MW? 20MW?) – FP6 UpWind Project Offshore plant would benefit from an appropriate power collection, transmission and distribution technology – HVDC potentially provides better efficiency, particularly over longer distances – Benefits from power semiconductor and copper cost trends

5 HVAC Transmission Systems Commonly used in many offshore wind farms Can suffer from excessive reactive current – Increases cable losses – Reduces power transfer capability – Reactive power compensation required (extra equipment) Can suffer from high line losses and excessive voltage drops – Extra cables required – Inter-dependant characteristics need careful consideration Transmission voltage level, cable capacitance and charging currents…

6 Existing HVDC Systems Modern HVDC systems generally have advantages such as: – Lower transmission losses – Fully controllable power flow – No reactive power generation or absorption (‘cable only’ connections) – Reduce/eliminate AC harmonic filter with the latest multilevel converter technologies (e.g. MMC HVDC) HVDC transmission systems can be categorised, by the converters used, into three categories: – Line-commutated Converters (LCC), Capacitor Commutated Converters (CCC) and Voltage Source Converters (VSC) as illustrated below Point to point HVDC power transmission – Wind Farm Inter-array? What do we want? – A dedicated high efficiency, robust, flexible and low cost power collection, transmission and distribution technology for use within the wind farm too

7 Proposed HVDC System HVDC power transmission from the point of generation – Reduce losses and components (i.e. make use of Turbine MV converter and availability of HVDC gird) Multi-terminal HVDC system – Increase availability Offers flexibility and redundancy – Reduce cost Removal of/minimise offshore substation Reduced cable losses (HV operation)

8 Proposed HVDC System Hybrid HVDC Transformer (figure shows simplified circuit) : – Steps up MVDC to HVDC – Reduced voltage stress on primary side and current stress on secondary side allows use of “off the shelf” force commutation devices – Uses magnetic transformer to avoid high conversion ratio – Potential to require less power capability from switches (30%) when compared with conventional 2-level 3-phase HVDC converter – Many potential challenges that need full investigation (e.g. switching control, network stability, economic impact, protection and isolation…)

9 Proposed HVDC System Switching device comparison: Proposed Hybrid HVDC Transformer vs. conventional HVDC converter (3-phase 2-level topology) – Assumptions n = number of series connected power switching devices in half of the bridge arm 6.5kV rated switching devices VSC-based HVDC converters use 3-phase, 2 (or multi) level converter topology Assumes 2 devices in series is sufficient to withstand the MV voltage stress – 150kVdc example HVDC side needs n >= 30 devices in series For conventional VSC-based HVDC systems – 6n >= 180 devices For hybrid HVDC transformer – 4n + 8 >= 128 devices – 29% saving in power semiconductors used

10 Selected Challenges The time to implement – Dependent on development/readiness of the offshore wind industry Managing multi-vendor solutions – Will this be a problem? Practical implementation (i.e. is it realistic?) – Needs further investigation; this is still a concept Will the subsea power cable size increase with no centralised collector? – Shouldn’t increase for similar voltage levels; the overall power stays the same Would a platform still be required as a maintenance hub? – A mobile platform could be used for this purpose Is there an operational impact? – Turbine operation should be unaffected – System optimum operation and control needs developing

11 Conclusions Potential advantages for offshore wind farm applications – An alternative to AC and point to point HVDC transmission topologies Suitable installation in every single power source – Increases flexibility and redundancy of the entire HVDC system Positive impact on wind farm availability and O&M costs – Eliminates/minimises the need for a centralised offshore collection platform Potential lower component count at converter level Modular component sets across the system – 100MW power block in centralised system vs. 20 x 5MW power blocks in hybrid HVDC transformer system Increased component count at system level (due to de-centralisation) – Balanced by no offshore substation and fewer components, e.g. fewer power semiconductors and filters…

12 Next Steps Investigate, in detail, the feasibility of this HVDC system concept – Detailed study of the proposed hybrid HVDC transformer Explore the feasibility of the following advantages: – High flexibility leading to ‘independent’ turbines – Additional redundancy and high system availability (no centralised substation) – High efficiency (power collection and O&M efficiency) – Cost reduction potential – Installation in individual turbines – Optimisation of materials (copper, semiconductor devices…) Investigate the use of SiC switching devices – Higher power density and heat tolerance

13 Thank you for listening! Narec Contact Details Technical Paper Authors:

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