rms vs emt: the need for new simulation tools€¦ · rms vs emt: the need for new simulation tools...
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Matas Dijokas, DTU
RMS vs EMT: the need for new
simulation tools
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Offshore AC grid and HVDC links
218 September 2019
• 5 wind power parks (Psum = 3.5 GW)
• Hub configuration: 220kV AC
• 5 HVDC links
• Hub connected to 3 synchronous
areas
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
VSC modelComponents and phasors
3
• Converter of MMC type
• Phase reactor – leakage inductance and series resistance of transformer
• Unity transformer ratio assumed
• Two converter control strategies:
– Grid following control
– Grid forming control
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Grid following control (Onshore VSC)
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Grid following control (Onshore VSC)
5
• Converter controls DC link voltage and
reactive power exchange at onshore station
• Outer and inner control loops use PI control
• Decoupled current control
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Grid forming control (Offshore VSC)
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Grid forming control (Offshore VSC)
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• Converter controls AC hub voltage and
active power sharing
• Two P-f control strategies:
– Different frequency droop values
– Same frequency droop values
• The frequency droop value kf selected
considering:
– Capability available on VSC
– Inertia of the onshore grids
• Converter equipped with Virtual
Impedance Control
18 September 2019
𝑃𝑖 = 𝑃𝑖𝑜 +
𝑘𝑓𝑖σ𝑗=1𝑛 𝑘𝑓𝑗
∙ ∆𝑃𝑤
Converter
Virtual Impedance Controller
Active Power Controller
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Is RMS still good enough to
analyse the dynamics of
zero-inertia systems?
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Time domain simulationsStudy case introduction
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Active power change:
1. Power request from onshore station
2. Wind power increase
Fault:
3. DC-link outage
18 September 2019
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Case 1: Power request from onshore station
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• Good match of RMS and EMT simulation regarding active power and frequency responses
• Slight mismatch between RMS and EMT model regarding hub voltage. EMT is able to detect high frequency
oscillations in hub voltage
• Overall, RMS model is appropriate when it comes to power exchange between the different onshore grids.
No need to consider the transmission cable dynamics
18 September 2019
Frequency VoltageActive power
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Case 2: Wind power increase
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• Good match of RMS and EMT simulations regarding the active power and frequency responses
• RMS model is unable to detect the maximum voltage deviation and high frequency oscillations in Hub-
voltage
• Overall, for wind power variation RMS model is appropriate when the focus is on active power and frequency
response. However, it fails to detect the maximum Hub-voltage deviation
18 September 2019
Frequency VoltageActive power
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Case 3: DC-link outage
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• The active power from the wind is exported from the hub
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Case 3: DC-link outage
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• The active power from the wind is exported from the hub
• DC-link outage simulated and isolated with two breakers
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Case 3: DC-link outage
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• The active power from the wind is exported from the hub
• DC-link outage simulated and isolated with two breakers
• Power redirected to remaining VSC links and determined by
frequency droop values kf
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Case 3: DC-link outage
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• No visible frequency mismatch between RMS and EMT models
• RMS model is unable to detect the maximum deviation and high frequency oscillations in Hub-voltage/active
power
• overall, for large disturbances (link-outage), RMS model fails to capture the dominant modes that
characterize the power and voltage responses
18 September 2019
Frequency VoltageActive power
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RMS vs EMT: the need for new simulation tools / Matas Dijokas ,DTU
Main takeaways
For the :
1. The simulations are able to to
capture the after a
2. The simulation reflects power changes and faults accurately, but requires
1618 September 2019
Need for new tools to capture the dynamics of zero-inertia
systems under fault, but remain computationally efficient
for large scale systems
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Thank You