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Abstract:
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This project presents the main features of each of the electricity transmission technologies available for
offshore wind power and discusses their advantages and disadvantages in terms of technical, economic and
environmental aspects. The transmission options studied are High Voltage Alternating Current (HVAC)
and High Voltage Direct Current (HVDC). Within the HVDC there are two transmission technologies
available, the classical Line Commutated Converter based HVDC and the most recently developed Voltage
Source Converter based HVDC. As technical features, both operational and implementation issues are
analyzed. Flexibility of control of active and reactive power or capacity to provide reactive power support
are examples of the first, and size of offshore substation is an example of the latter. Cost-effectiveness and
system losses are compared to derive a general rule for the best transmission option from the economic point
of view and environmental concerns are also addressed. This enables reader to have a general overview of
the factors that affect the decision of using one transmission technology or the other.
The second part of the project is centered in the modeling and simulation of a particular case study using
HVDC and HVAC. The studied system consists of a Full Scale Converter (FSC) based wind farm which is
located 50 km off the shore. The wind farm has a rated power of 100MW which needs to be transmitted
to the onshore grid either via VSC based HVDC or HVAC. Two models are built in order to learn about
and implement the control systems of the converters. A detailed explanation on the control system design
is included. Special attention is given to control strategies to comply with grid regulations related to fault
ride-through capability and reactive power support. German Grid Codes are chosen as reference. In the
case of HVDC reactive power support is performed by the grid-side VSC of the HVDC system, whereas in
the case of HVAC it is performed by the grid-side converters of the wind turbines. Strategies to reduce the
electrical power generated by the wind farm in case of fault on the onshore grid include a chopper placed
on the HVDC link for the HVDC solution and a chopper placed on the wind turbine converter’s DC link
for the HVAC solution. |
