FixReF: A control strategy for offshore wind farms with different wind turbine types and diode rectifier HVDC transmissionOffshore wind farms built at a long distance from the onshore grid are connected via HVDC-transmission. Future HVDC-systems may connect offshore wind farms via uncontrolled diode rectifiers instead of VSC-HVDC converters. Due to this wind turbine inverters must own a grid forming capability. This paper describes a control strategy that requires only minor changes in the conventional wind turbine inverter control software to form the AC-voltage in the offshore island grid. It is shown that this strategy allows an interconnection of different wind turbine types considering auxiliary power supply and reactive power sharing.
Voltage and current behavior in a FixReF controlled offshore wind farm using a HVDC transmission system based on uncontrolled diode rectifier unitsFuture HVDC systems may connect offshore wind farms via uncontrolled diode rectifiers instead of VSC-HVDC converters. Due to this wind turbine inverters must own a grid forming capability. This paper describes a control strategy that requires only minor changes in the conventional wind turbine inverter control software to form the AC voltage in the offshore island grid connected via diode rectifier HVDC link.
FixReF sinusoidal control in line side converters for offshore wind power generationA common power converter control principle is the application of a DQ-control in a rotational frame. This principle enables the controller to consider active and reactive current as DC-values. This paper describes a control system based on a fixed frame. It prevents the controller from applying the DQ-current control algorithm to avoid patent violation at once. Simultaneously this algorithm provides the opportunity to control accurately the negative sequence system of the converter currents. Simulation results as well as experimental investigations on a converter test bench prove the beneficial functionality of the so called sinusoidal control principle. In addition a method is introduced improving stability issues and allowing island operation of voltage source converters with sinusoidal current control.
A fault handling current control strategy for offshore wind turbines in interconnected offshore wind farms with different types of HVDC transmissionOffshore wind turbines built at a long distance from public ac-grid are connected via HVDC-transmission. Future HVDC-systems may connect offshore wind farms via uncontrolled diode rectifiers instead of VSC-HVDC converters. Due to this wind turbine inverters must own a grid forming capability. This Paper describes a fault handling strategy for offshore the wind turbines during faults in the ac-offshore island grid. The control strategy is based on a fixed reference frame current source operation of all line side converters in the wind farm.
DFIG wind turbines operating in a fixed reference frameHVDC connected offshore wind farms represent a weak grid that causes stability issues in voltage oriented controlled converters. In addition the conventional line side converter control is not applicable for island grids without an existing AC-voltage source. A Fixed Reference Frame (FixReF) control proved already beneficial in full scale converter wind turbines. In this paper, the usage of FixReF in wind energy plants with doubly fed induction generators is investigated.