Protection Strategies for the Connection of Diode Rectifier-based Wind Power Plants to HVDC Interconnectors

Abstract

[EN] The connection of diode rectifier (DR) based wind power plants to existing or planned High Voltage dc (HVdc) interconnectors can lead to important savings on cost and system robustness. Since the DR station usually operates in a bipolar configuration, its connection to symmetric monopoles is particularly challenging. However, there are no published detailed studies on the protection of DR connection wind power plants to symmetric monopole interconnectors or even to bipolar interconnectors. This paper includes the comparative study of five different protection strategies for such systems, including both solid and resistive DR station grounding and strategies with and without the use of dc-circuit breakers. An analytical study allows for the calculation of fault current during fault on-set for both half-bridge and hybrid Modular Multi-level Converter (MMC) stations. Using detailed Electromagnetic Transient (EMT) simulation studies, the different protection strategies are evaluated in terms of current, voltage and isolation requirements of each element, as well as the need for dc-circuit breakers, fast communication or larger surge arresters. Moreover, a distance fault detection algorithm is included for the wind turbine converters to distinguish between local ac-grid and dc-cable faults. From the simulation results it is possible to conclude that DR high impedance grounding, together with wind turbine distance protection can be used for the protection of DR based off-shore wind power plants connected to symmetric monopole interconnectors without requiring dc-circuit breakers.