Title: Control of a multiterminal VSC transmission scheme for connecting offshore wind farms
1Control of a multi-terminal VSC transmission
scheme for connecting offshore wind farms
European Wind Energy Conference 2007, Milan
Ralph L. Hendriks (R.L.Hendriks_at_tudelft.nl), G.
C. Paap, W. L. Kling
2Contents
- Offshore wind farms and interconnectors
- Voltage-sourced converter model
- Voltage-sourced converter controls
- Simulation study
- Conclusions
3Offshore wind farms and interconnectors
- Offshore wind has a good potential as a source of
renewable energy - Current offshore wind farms located relatively
close to shore (12-miles zone) - Future farms will be located further offshore
- Grid connection costs will dominate wind farm
project budgets
4Capacity factor
- Transmission system capacity utilization is
dictated by wind stochastics - Capacity factor offshore wind farm 3545
- Transmission costs per unit energy are relatively
high
5Offshore wind farms and interconnectors
- Since the liberalization of electricity markets,
a growing demand for interconnection capacity
exists - Cross-border interconnectors have been build to
share regulating and reserve power - Cross-border interconnectors are now the backbone
for international trade
6Priority axes for interconnector capacity
development
Source TEN-E project documentation, DG TREN
7Combination of interconnector and wind farm
- Proposed interconnector routes cross promising
wind farm sites - Maximization of cable utilization lowers
transmission costs - Use same infrastructure for grid connection and
energy trade - DC technology unavoidable, how to control and
dispatch power?
8Combination of interconnector and wind farm
9AC versus DC transmission
- AC transmission through submarine cables has
technical limitations ? maximum 100 km - DC transmission ? only resistive losses ?
unlimited transmission distance - Line-commutated converter (LCC) technology versus
voltage-sourced converter (VSC) technology
10Voltage-sourced converter (VSC)
- Independent control of active and reactive power
- Provides local voltage support
- Power flow can be reverted by voltage polarity or
current direction
11VSC equivalent model
12Vector control
- Fast inner loop controls id and iq
- D-Q-Z type PLL tracks the utility voltage phase
angle - Decoupling iq controls P, id controls Q
- Current references obtained by slower outer-loop
controllers
13DC-voltage control
- DC voltage is a measure for unbalance in the DC
system - At least one controller in the scheme should
regulate the DC voltage - No additional signals or telecommunications are
required balancing - Compare power/frequency control in ac grids
14DC voltage control
- DC voltage control by straightforward
PI-regulator - Only P-control when more than two terminals are
present - Controller can be offset by P0
- power dispatch on the link, centralized
controller with telecommunication links
15Simulation study
- System modelled in Matlab/Simulink
- Three identical converters rated 300 MW
- Total link length 200 km (purely resistive)
- 300 MW wind farm connected to middle terminal
16Simulation study-50 MW step in wind farm infeed
17Simulation studyControlled shut-down of wind farm
18Conclusions
- Combination of wind farm grid connection and
interconnector is a promising cost-saving
alternative - Proof-of-concept first step in development of
pan-European offshore grid - DC voltage is a measure for unbalance
- No telecommunications-in-the-loop required
- Simplified VSC model that can be included in
power system simulation software
19Control of a multi-terminal VSC transmission
scheme for connecting offshore wind farms
European Wind Energy Conference 2007, Milan
Ralph L. Hendriks (R.L.Hendriks_at_tudelft.nl), G.
C. Paap, W. L. Kling