demo 1 - bestpaths- · pdf fileto demonstrate the results in a laboratory environment using...

DEMO 1DEVELOPMENT OF A DC FACILITY TO SIMULATE OFFSHORE MULTITERMINAL HVDC GRIDS AND THEIR INTERACTION WITH WIND GENERATORS

22 November 2017

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Salvatore D’Arco, SINTEF Energy Research

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• Wind energy will be the most widely adopted renewable energy source (RES) by 2050to contribute towards the abatement of green house gas emissions.

• Due to its technical advantages, operators and manufacturers are now consideringHVDC solutions over HVAC to evacuate the energy from offshore wind farms

• Voltage source converter (VSC) based schemes are becoming the preferred optionover line commutated converter (LCC) alternatives due to their decoupled power flowcontrol, black-start capability and control flexibility.

• MTDC grids will facilitate a cross-border energy exchange between different countriesand will enable reliable power transfer from offshore wind farms (OWFs).

• The interactions between wind turbine converters and different VSC converter types ina meshed topology need further investigation.

INTRODUCTION

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DEMO1 OBJECTIVES

1. To investigate the electrical interactions between HVDC link converters and windturbine converters in offshore wind farms.

2. To de-risk the multivendor and multiterminal schemes in terms of resonances, powerflow and control.

3. 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 toemulate the AC grid).

4. To use the validated models to simulate a real grid with offshore wind farmsconnected in HVDC.

DEMONSTRATOR: finalised tasks

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• Three MMC converters were designed from scratchfor Best Paths

• MMC with HB cells, 18 cells per arm

• MMC with FB cells, 12 cells per arm

• MMC with HB cells, 6 cells per arm

• During this year all the converter components havebeen built and successfully tested at full rating

• 42 modules

• 144 power cell boards

• 1764 capacitors

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• The converters developed were installed in the Norwegian National Smart GridLaboratory, jointly operated by SINTEF Energy Research and the Norwegian University ofScience and Technology

• Detailed description in Deliverable 8.1 (available for download in the project website)

• Demoed for companies outside Best Paths in May during a special dissemination event

• The facility will be available to any stakeholder after the project ends


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• The converters were commissioned in June with the collaboration of experts fromEnerginet

• Deliverable 8.2 will include the results of the tests carried out in the demonstrator, aswell as the report of the commissioning of the converters.


Conv12 700UDC, 100% active current Id (-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

DEMONSTRATOR: work in progress

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• Gamesa’s WF model is being adapted to run in the 200 kVA high-bandwidth gridemulator that is available in the laboratory

• An improvement to the initial the scope: D8.2 will be updated with results at a later stagenext year

• Power Hardware in the Loop implementation combining the real time simulator and the gridemulator

Flexibility in the model simulated

Possibility to reproduce faster dynamics

IA

IB

IC

IA*

IB*

IC*

UA

UB

UC

Real Time Wind Farm Model UA*

UB*

UC*

Grid EmulatorReal Time Simulator

Current References

Voltage Measurements

DEMONSTRATOR: work in progress

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• We are currently running tests to evaluate the accuracy of the models to represent thedemonstrator

28 29 30 31 32 33

-80

-60

-40

-20

0

20

40

60

80

Time (s)

Id (

A)

Demonstrator

Model

4 4.01 4.02 4.03 4.04 4.05-20

-10

0

10

20

30

40

Time (s)

Arm

Curr

ent (A

)

Model

Model

Demonstrator

Demonstrator

4 4.01 4.02 4.03 4.04 4.05660

670

680

690

700

710

720

Time (s)

Cell

Voltage (

V)

DEMONSTRATOR: next steps

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• Complete the matching of the models and demonstrator (November)

• Define the final tests to be carried out (November)

• Document results in D8.2 (December)

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Max Parker, University of Strathclyde

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SIMULATION MODELS: finalised tasks

• A set of models and control algorithms has been developed, simulated and assessed

• Their portability as basic building blocks will enable researchers and designers to study and simulate any system configuration of their choice

• These have been published in the BEST PATHS website as a MATLAB/ Simulink ‘Open Access’ Toolbox


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• The user manual comes with the published models and accompanying examples

• Specific blocks include models of:

o High level controllers

o Converter stations

o AC grid

o DC cables

o Wind farm

• Detailed descriptions available in Deliverable 3.1


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• During this year Deliverable 3.2 Results and conclusions from Simulationsand studies in Demo 1 was published. Public version available for downloadat http://www.bestpaths-project.eu/en/publications

• D3.2 includes the calculation of all the KPIs that were defined for WP3(more details in D2.1)


Due to converter overloading and DC overvoltage during extreme conditions (e.g. AC faults). Overloading sustained for a very short time <300ms and braking resistor prevents overvoltage.

Due to steady-state error between actual and reference active power during frequency oscillations on the AC grid of Topology A & B.

KPI Assessment Summary

SIMULATION MODELS: work in progress

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• Matching of models and demonstrator

o Increases accuracy

o Real measurements compared against simulations

o Model parameters tweaked until results are as similar to themeasurements as possible

o Parameters to match:

Transformer magnetisation inductance and resistance

Transformer leakage inductance and copper resistance

• Nameplate values used

Cell capacitor ESR

• Small effect, chosen based on datasheet.

Arm Inductance

• Includes any parasitics

Arm Resistance

• Combined resistance of arm inductors, MOSFETs, PCBs, cables etc.

Controller delay

Voltage measurement delay (relative to current)

Matching of Transformer Parameters – estimated from open-circuit tests

Magnetising reactance:

𝑋𝑚 =3𝑉𝑝ℎ

2

𝑄𝑜𝑐

Results for 18-level:

Value for 330V used

Iron-loss resistance:

𝑅𝑚 =3𝑉𝑝ℎ

2

𝑃𝑜𝑐

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0

50

100

150

200

250

300

0 100 200 300 400

Rm

PU

Vph (V)

23.5

24

24.5

25

25.5

26

26.5

27

27.5

0 100 200 300 400

Xm

PU

Vph (V)


Noise and offset more apparent due to low current flow.

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Matching of Transformer Parameters – estimated from open-circuit tests


• Tuned iteratively, based on arm current and cell voltage measurements.

• Unknown delay between cell voltage and arm current measurements.

• Therefore cannot just match up waveforms directly.

• Matched based on:

• Magnitude and phase of second harmonic of arm current.

• Ratio of second harmonic of cell voltage to second harmonic of arm current.

• Match these parameters, then measure V-I delay off waveform.

• Sensitivity studies carried out to determine effects of:

• Varying cell capacitance

• Varying magnitude of arm impedence at 100Hz

• Varying phase of arm impedence at 100Hz (i.e. amount of resistance vs. inductance).

• Matching of internal parameters carried out using open-loop control with resistive load.

• Testing at 300V and 11Ω load for minimum noise. Verified at lower powers.

Matching of cell capacitance, arm inductance, resistance


0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

0.7 0.8 0.9 1 1.1 1.2

Zarm Magnitude

I2/I1 I2/V2

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Matching of arm inductance: effects of varying magnitude


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2 4 6 8 10

I2 P

has

e

Zarm angle

Matching of arm inductance: effects of varying angle


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0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

0.017 0.019 0.021 0.023

Cell Capacitance (mF)

I2/I1 I2/V2

Matching of cell capacitance


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Matching of voltage and current


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Matching of arm current and cell voltage


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Islanded mode, with AC and DC current controllers active.

Used 3-phase instantaneous RMS current:

5 simulation time step delay (400µs) found to give best result.

Delay between cell voltage and arm current also around 400µs.

𝑖𝑟𝑚𝑠 =𝑖𝐴2 + 𝑖𝐵

2 + 𝑖𝐶2

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Matching of controller delays


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Matching of controller delays, non-islanded



Demonstrator Parameters (expected values in brackets)

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18-level 12-level 6-level

SubmoduleCapacitance (mF)

22.8 (19.8) 15.1 (15.0) 6.71 (7.5)

Arm inductance(mH)

1.555 (1.5) 1.534 (1.5) 1.539 (1.5)

Arm resistance(mΩ)

90(17 for MOSFETs)

100(22 for MOSFETs)

100(19 for MOSFETs)

Vcell-Iarm delay 400µs, 5 steps

I-control delay 400µs, 5 steps

THANK YOU!

QUESTIONS?

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demo 1 - bestpaths- · pdf fileto demonstrate the results in a laboratory environment using...

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