Modelling and analysis of CIGRE HVDC offshore multi-terminal benchmark grid

Trondheim, February 2015

Jordi Pegueroles Queralt, Mike Barnes, Oriol Gomis-Bellmunt, Antony Beddard and Fernando D. Bianchi

INDEX

• Motivation • System Description

• Control of HVDC converters • Power Control

• Droop control • Modelling components

• DC line model • DC grid

• Small signal models • AC and DC dynamics

• Dynamics with DeadBand • MT-HVDC dynamics

• Simulations Results • Conclusions

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Motivation, 4-terminal HVDC benchamrk system by CIGRE

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500 MW

400 MW

100 MW

800 MW

300 MW

AC voltage control

DC Dead Band control

DC Droop control

DC Droop control

The objective is this study is to analyse of the stability and transient performance of the 4-terminal HVDC system

INDEX

• Motivation • System Description

• Control of HVDC converters • Power Control

• Droop control • Modelling components

• DC line model • DC grid

• Small signal models • AC and DC dynamics

• Dynamics with DeadBand • MT-HVDC dynamics

• Simulations Results • Conclusions

4

Power control of HVDC converters

5

0 dB

ω

|·|

General control scheme for HVC converters and control loop bandwidths

Qualitative bode diagram

Line Modelling: n T sections line model

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4 input / 4 output DC-Grid

HVDC line model

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The dynamics of the line are comparable with the dynamics of the converters

Analysing the physical specifications of the cable, and taking into account the presence of a return line, we have concluded that a slightly modified values from the ones used in the CIGRE model are more accurate for the study.

INDEX

• Motivation • System Description

• Control of HVDC converters • Power Control

• Droop control • Modelling components

• DC line model • DC grid

• Small signal models • AC and DC dynamics

• Dynamics with DeadBand • MT-HVDC dynamics

• Simulations Results • Conclusions

8

AC and DC small signal models

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VSCk

G-ACk DC-Grid +

MT-HVDC grid

Sigma plot of the MT-HVDC system

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MT-HVDC grid

Normal operation

Sigma plot of the MT-HVDC system

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MT-HVDC grid

Dead band operation on the offshore wind farm

Pole location of the MT-HVDC system

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MT-HVDC grid

Dominant poles of the closed loop

system

Pole location of the MT-HVDC system

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MT-HVDC grid

Dominant poles of the closed loop

system

INDEX

• Motivation • System Description

• Control of HVDC converters • Power Control

• Droop control • Modelling components

• DC line model • DC grid

• Small signal models • AC and DC dynamics

• Dynamics with DeadBand • MT-HVDC dynamics

• Simulations Results • Conclusions

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Conclusions

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The MT-HVDC system is stable, but the interaction among the droop controllers presents a oscillatory response in the DC voltage variation, as well as on the power output

Conclusions

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The response of the MT-HVDC system without one of the droop converters presents a faster extintion rate than the previous case. This is also produced by the faster response of the DeadBand control of the OWP

INDEX

• Motivation • System Description

• Control of HVDC converters • Power Control

• Droop control • Modelling components

• DC line model • DC grid

• Small signal models • AC and DC dynamics

• Dynamics with DeadBand • MT-HVDC dynamics

• Simulations Results • Conclusions

17

Conclusions

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• Careful coordination on the droop control is required, as parallel operation of droop controllers results in oscillatory response.

• The parameters and model of the HVDC cables have to be carefully chosen to match the frequency range of the study.

• The transient performance of the system can be improved with a more sophisticated droop control scheme.

Acknowledgements

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