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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. Outline of Presentation. North Sea Connection VSC-HVDC Control strategy DC-voltage droop control
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Generalised Droop Control for Power Management in a Multi-Terminal HVDC System Kamila Nieradzinska, Grain Adam, W. Leitheadand Olimpo Anaya-Lara University of Strathclyde
Outline of Presentation • North Sea Connection • VSC-HVDC • Control strategy • DC-voltage droop control • Test system configuration • Results • Conclusions
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)
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
Point-to-point Connection Different control strategies employed for offshore wind farm and onshore grid.
Vector Control • Three-phase rotating voltage and current are transformed to the dqreference 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.
Control Strategies – Inner Controller Inner Controller Responsible for controlling the current in order to protect the converter from overloading during system disturbances
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
Wind farm side VSC Controllers Schematics Active power and AC voltages control Onshore grid side VSC DC and AC voltages 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: DC Voltage Droop Control
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. Conclusions