Generalised Droop Control for Power Management in a Multi-Terminal HVDC System - PowerPoint PPT Presentation

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Generalised Droop Control for Power Management in a Multi-Terminal HVDC System

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Phase-locked-loop (PLL) is used to synchronize the modulation index. There is a large Disadvantages with the traditional control approach which is that power must me ... – PowerPoint PPT presentation

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Title: Generalised Droop Control for Power Management in a Multi-Terminal HVDC System


1
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2
Generalised Droop Control for Power Management
in a Multi-Terminal HVDC System
  • Kamila Nieradzinska, Grain Adam,
  • W. Leithead and Olimpo Anaya-Lara
  • University of Strathclyde

3
Outline of Presentation
  • North Sea Connection
  • VSC-HVDC
  • Control strategy
  • DC-voltage droop control
  • Test system configuration
  • Results
  • Conclusions

4
North Sea Connections
5
What 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)

6
Why 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

7
Point-to-point Connection
  • Different control strategies employed for
    offshore wind farm and onshore grid.

8
Vector 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.

9
Control Strategies Inner Controller
  • Inner Controller
  • Responsible for controlling the current in order
    to protect the converter from overloading during
    system disturbances

10
Control 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

11
Controllers Schematics
Wind farm side VSC
Active power and AC voltages control
Onshore grid side VSC
DC and AC voltages control
12
DC 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
 
13
Test System Configuration
14
Power 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
15
DC Voltage Droop Control ON
16
Test System Configuration with Loss of VSC4
17
Power 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
18
Conclusions
  • 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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