Hardware Testing of Sliding Mode Controller for Improved Performance of VSC-HVDC Based Offshore Wind Farm Under DC Fault

This paper proposes a sliding mode control (SMC) method for an onshore voltage source converter (VSC) used in a high-voltage-direct-current (HVDC) transmission system. The onshore VSC-HVDC station is based on a two-level voltage converter topology that is used to interconnect an offshore wind farm (OWF) with the ac main grid via two dc cables. The OWF is composed of ten variable speed wind turbines based on permanent magnet synchronous generators (VSWT/PMSGs). The VSWT/PMSGs are connected in parallel to a common dc bus. The ac main grid receives the required active power from the OWF through a transformer, 12-pulse diode rectifiers, boost converters, two dc cables, and a VSC-HVDC station. The boost converters are used to operate at speeds for maximum power extraction from the VSWT. SMC is used to ensure a stable operation of the VSC-HVDC station during dc fault, as well as to avoid controller saturation, a behavior that is usually seen when using linear controllers. The effectiveness of the proposed control method on system operation under dc fault is demonstrated by simulations carried out using matlab/Simulink. In addition, a scaled-down laboratory prototype of the system is built and tested to validate the performance of the proposed control scheme.