Title: Generalised Droop Control for Power Management in a Multi-Terminal HVDC System
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2Generalised Droop Control for Power Management
in a Multi-Terminal HVDC System
- Kamila Nieradzinska, Grain Adam,
- W. Leithead and Olimpo Anaya-Lara
- University of Strathclyde
3Outline of Presentation
- North Sea Connection
- VSC-HVDC
- Control strategy
- DC-voltage droop control
- Test system configuration
- Results
- Conclusions
4North Sea Connections
5What is VSC
- VSC Voltage Source(d) Converter
- Capacitor is normally used as energy storage
- VSC uses a self-commutated device such as GTO
(Gate Turn Off Thyristor) or IGBT (Insulated Gate
Bipolar Transistor)
6Why VSC-HVDC
- Power transfer over long distances
- Lower power losses compared to AC transmission
- Independent control over active and reactive
power - Voltage support
- Wind farm is decoupled from the onshore grid,
- Connected to the weak network
- Black start capability
7Point-to-point Connection
- Different control strategies employed for
offshore wind farm and onshore grid.
8Vector Control
- Three-phase rotating voltage and current are
transformed to the dq reference frame - Comparative loops and PI controllers are used to
generate the desired values of M and ? and fed
their values to the VSC - Phase-locked-loop (PLL) is used to synchronize
the modulation index.
9Control Strategies Inner Controller
- Inner Controller
- Responsible for controlling the current in order
to protect the converter from overloading during
system disturbances
10Control Strategies Outer Controller
- Outer controller
- Responsible for providing the inner controller
with the reference values, where different
controllers can be employed, such as - DC and AC voltage controllers
- The Active and reactive power controllers
- The frequency controller
11Controllers Schematics
Wind farm side VSC
Active power and AC voltages control
Onshore grid side VSC
DC and AC voltages control
12DC Voltage Droop Control
The proposed droop control provides a reference
voltage to the DC voltage controller i taking
into account the voltage at the support node j
as shown in equation
13Test System Configuration
14Power Balance Droop Control ON
Time 0 - 1.5 1.5 - 3 3 4.5 4.5 - 6 6 7.5 7.5 - 9
VSC3 255 450 350 255 160 65
VSC4 255 175 220 255 295 330
VSC5 255 140 195 255 310 370
15DC Voltage Droop Control ON
16Test System Configuration with Loss of VSC4
17Power Balance Droop Control ON (No VSC4)
Time 0 - 1.5 1.5 - 3 3 4.5 4.5 - 6 6 7.5
VSC3 33.3 50 62.5 50 75
VSC4 33.3 25 0 0 0
VSC5 33.3 25 37.5 50 25
18Conclusions
- The controller can respond to any power demand
- There are significant advantages in terms of
power flow controllability - This can prove to be very advantageous for
connection of variable wind generation and assist
in the power balancing of interconnected networks.
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