A Demonstrator for Experimental Testing Integration of Offshore Wind Farms With HVDC Connection. S.D'Arco, A. Endegnanew, SINTEF Energi

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1 A Demonstrator for Experimental Testing Integration of Offshore Wind Farms With HVDC Connection S.D'Arco, A. Endegnanew, SINTEF Energi

2 BEST PATHS PROJECT BEyond State-of-the-art Technologies for re-powering AC corridors and multi-terminal HVDC Systems Validate the technical feasibility, impacts and benefits of novel grid technologies, Five large-scale demonstrations Deliver solutions that allow for transition from High Voltage Direct Current (HVDC) lines to HVDC grids; Upgrade and repower existing Alternating Current (AC) parts of the network; Integrate superconducting high power DC links within AC meshed network 3

3 LARGE SCALE DEMONSTRATIONS 1. HVDC in offshore wind farms and offshore interconnections 2. HVDC-VSC multivendor interoperability 3. Upgrading multiterminal HVDC links 4. Innovative repowering of AC corridors 5. DC Superconducting cable Upgrading of existing AC grids From HVDC lines to HVDC grid 4

4 DEMO 1 Objectives To investigate the electrical interactions between HVDC link converters and wind turbine converters in offshore wind farms. To de-risk the multivendor and multiterminal schemes: resonances, power flow and control. To demonstrate the results in a laboratory environment using scaled models (4-terminal DC grid with MMC VSC prototypes and a Real Time Digital Simulator system to emulate the AC grid). To use the validated use the validated models to simulate a real grid with offshore wind farms connected in HVDC. 5

5 6 Substation Wind farm

6 7

7 HVAC HVDC Substation Wind farm 8

8 Demonstrator overview Three-terminal scheme MMC with MMC with HB cells, 18 cells and 6 cells per arm, MMC with FB cells, 12 cells per arm Wind farm emulator Wind farm emulator National smart grid laboratory 9

9 National Smart Grid Laboratory Laboratory formally opened in September 2016 after a major upgrade Jointly operated by NTNU and SINTEF Reconfigurable layout with multiple ac and dc bus 10 Power electronics converters 2 level VSC 60 kva, MMC 60 kva Electrical machines Synchronous generators, Induction machines Real-time simulator

10 Real-time simulation and PHIL capabilities OPAL-RT based real time simulator platform 5 parallel cores, 2 FPGAs for IO and small time step simulation, Fiber optic communication Egston Compiso Grid emulator 200 kva rated power 6 individual outputs > 10 khz bandwidth Connected to the OPAL-RT system via fiber optics with 4 µs update rate for measurements and references 11

11 Demonstration of HVDC transmission systems connected to offshore wind farms Designed and built 3 MMC prototypes Tested the converters in point to point and multiterminal configurations Planned PHIL experiements with real time model of a wind farm Offshore Grid #1 Vac_w2 WFC #2 Offshore Onshore Offshore Grid #1 V ac_w1 WFC Offshore Onshore GSC P g1,q g1 Onshore AC Grid #1 Pw2 Vac_w2* AC Voltage Control fw12* θw2* DC NETWORK P w1 DC CABLE Vdc_g1 Offshore Grid #1 Vac_w1 WFC #1 Vdc_g1 GSC #1 Pg1,Qg1 Onshore AC Grid #1 V ac_w1 * AC Voltage Control f w1 * θ w1 * V dc_g1 * V dc and Q Controller Q g1 * Pw1 Vac_w1* AC Voltage Control fw1* θw1* Vdc_g1* (Vdc vs. P) and Q Controller Qg1* 12

12 MMC Converters Three MMC converters were designed from scratch MMC with HB cells, 18 cells per arm MMC with FB cells, 12 cells per arm MMC with HB cells, 6 cells per arm Built and successfully tested at full rating 42 modules 144 power cell boards 1764 capacitors 13

13 14 Power cell boards

14 15 Assembling stages

15 Converter performance test Conv12 700UDC, 100% active current I d (-81.2A) Phase C upper arm voltage, Phase C Lower arm voltage, Phase C output voltage, Phase C arm current Conv18 700UDC, 24.3kW,7.8kVar Phase C upper arm voltage, Phase C Lower arm voltage, Phase C output voltage, Phase C arm current 16

16 Point-to-point and multiterminal configurations Tests to evaluate the accuracy of the models to represent the demonstrator Id (A) Demonstrator Model Arm Current (A) Model Model -10 Demonstrator Demonstrator Time (s) Time (s) Cell Voltage (V) Time (s)

17 Wind farm emulator Voltage Measurements Wind farm model is adapted to run in the 200 kva high-bandwidth grid emulator Real Time Wind Farm Model Real Time Simulator IA IB UA* UB* Grid Emulator IA * UA IB * UB IC * IC UC* UC PHIL implementation combining the real time simulator and the grid emulator Flexibility in the model simulated Possibility to reproduce faster dynamics Current References 18

18 Interaction of an offshore wind farm with an HVDC Complex issues Noise, randomness of event timings, and hardware design Low cost Moderate cost High cost Numerical simulations are widely accepted and cost effective Test a wide variety of different cases, however, the fidelity of the results is difficult to assess. 19 Hardware power-in-the-loop (HIL) simulation offers a good balance between test coverage and fidelity.

19 PHIL experiment: Wind farm connected to VSCbased HVDC Simulated wind farm Real-time simulator Grid emulator iabc* Measurement points GE HW Input: Wind speed and measured voltage Output: Grid emulator reference current Hardware Two-level VSC generates a three-phase ac voltage with a fixed frequency The close-loop behaviour of the PHIL setup was stable VSC controller (Island mode) Wind farm simulation v d *=1 pu v q*=0 f 2π 1 s - abc dq iabc * HVDC dc voltage refeence vabc Transf. VSC ~ = vabc 20

20 Results Simulation Hardware Angular vel. (rpm) Wind speed (m/s) Voltage (V) 21 Power (pu) Current (A)

21 Conclusions Power hardware-in-the-loop (PHIL) approach combines hardware devices with software simulation. The hardware part allows a high fidelity of the results whereas, the software simulation part allows an extensive study of different cases at a reasonable cost Grid integration of wind farm using VSC-based HVDC system was evaluated in PHIL experiment as a proof of concept. In the future work,phil implementation using modular multilevel concepts will be studied 22

22 Teknologi for et bedre samfunn