Medium frequency diode rectifier unit based HVDC transmission for offshore wind farm integration

Abstract

The offshore wind farms are the main trend of the wind power development in the future. The medium frequency diode rectifier unit based high voltage direct current transmission system is proposed here for offshore wind farm integration. Unlike conventional high voltage direct current solutions, the rated frequency of the offshore alternating current (AC) grid is increased to about 100∼400 Hz in the proposed system. Besides, a grid‐forming control scheme for the wind turbine converters is also proposed in this paper, where the machine side converter controls the direct current (DC) voltage and the grid side converter controls its output alternating current voltage in the global unified reference coordinate system. As a result, smaller and lighter passive components, such as the transformers, alternating current filters and reactive power (VAR) compensators, could be adopted in the offshore grid, which is beneficial for achieving higher economic efficiency. The small stability analysis and the time domain simulation of the proposed system are carried out based on a simplified model and power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) respectively, and the feasibility of the proposed schemes is verified.

Overview of frequency control techniques in power systems with high inverter‐based resources: Challenges and mitigation measures

“…They are more dynamic in power reversal and typically smaller in size due to smaller filters. For multi-terminal HVDC grids, VSCbased technology is preferred, and most offshore wind farms use VSC-based HVDC configuration [95]. Offshore converter stations regulate AC voltage and frequency in islanded mode, and voltage source converter (VSC) converters can be used as a current source in the GFL mode [96] topologies due to high efficiency, superior output waveforms, and scalability [97].…”

Harmonic filtering and fault ride‐through of diode rectifier unit and modular multilevel converter based offshore wind power integration

“…According to the synchronization scheme, the existing control strategies of grid‐forming WTs can be divided into three categories: (1) References [14–16] proposed the phase‐locked loop (PLL)‐based strategy without communication links, while the PLL tends to cause system instability in weak grids. (2) The global reference angle‐based strategy without PLL is proposed in [17–18], while the global signal is needed for all WTs. (3) In [19–22], the reactive power/frequency droop‐based strategy is proposed, which seems to be preferable due to no PLL or communication link.…”

A dynamic equivalent aggregation method of wind turbine systems with a full‐scale power converter for electromagnetic transient simulations

“…It was also forecasted that 76 GW of new capacity will be installed by 2020 [5]. Owing to the randomness and intermittence of wind energy, the impact of large-scale wind farm (WF) integration is worth of concern for modern power systems [6][7][8]. As WF with gigawatt capacity may contain hundreds of individual wind turbine systems (WTSs), the detailed time-domain simulation including every WTS is infeasible.…”