A NEW CONTROL METHOD FOR FAULT-RIDE-THROUGH OF HVDC-CONNECTED OFFSHORE WIND PARKS

The Multilevel Modular Converter (MMC) has been established as a preferred topology in the field of Voltage Sourced Converter for High Voltage DC (HVDC) transmission. Traditionally, supplementary equipment, for example, a Dynamic Braking System (DBS), is employed to temporarily dissipate the dc power transmitted from the OffshoreWind Parks (OWP) if the onshore grid is unable to absorb the totality of the generated power by the OWP. Such a reduction in power transfer requirement may be due to a fault in the converter station or in the attached ac network. The DBS circuitry requires considerable space and is costly. Due to the limited energy storage capacity embedded within the HVDC system, active power balancing is only possible in coordination with the connected power park modules. The need for control and compensation of converter energy within the valve submodules is paramount to guarantee the correct operation of the converter under normal or abnormal operating conditions. This paper shows two control methods of the offshore converter to provide fault-ride-through capability at the onshore ac grid without the need of a DBS. This is achieved by controlling the frequency and/or the ac voltage magnitude of the offshore ac grid. The concept has been validated by simulation results in PSCAD.