Abstract:
The increased demand for electricity has led to a global energy transition towards the use of renewable energy sources for power generation. Renewable energy has several advantages such as high efficiency, resource availability, cost competitiveness and environmental adequateness, compared to conventional fossil fuel power plants. Recent research studies have therefore focused on developing renewable energy technology. In fact, for alternating current (AC) collection grids, each wind energy conversion system (WECS) on a wind power plant (WPP) includes a wind turbine plus mechanical parts (i.e. gearbox), a generator (squirrel cage induction generator (SCIG), doubly fed induction generator (DFIG), permanent magnet synchronous generator (PMSG)), and a massive 50 or 60 Hz power transformer including controller circuit. A wind farm with a direct current (DC) transmission link is considered for this study. For a wind farm employing DC collection grid, the massive power transformers in the WECSs are replaced by the power electronic converters. The power electronic converter is significantly more compact and smaller in size compared to a power transformer of identical features. High voltage DC (HVDC) power transmission and distribution systems play an integral role in power systems and renewable energy resources integration technology.
The WPPs have to play an essential function in maintaining grid stability due to the continuous progress in the number of grid-connected wind farms. This growth requires the wind turbine generator (WTG) on wind farm to stay connected to the power grid for any fault conditions. The fault ride-through (FRT) capability is the ability of WECS to stay connected for short periods of fault conditions. This expression can also be used to demonstrate the ability of a wind farm to participate in the voltage stability during grid faults. This study proposes integration of the wind energy conversion unit (WECU) three-phase controlled switch active converters. Two configurations for the converters are considered:
Vienna rectifier-I
Modular multi-level converters (MMC)
In these configurations, the switching loss is reduced due to a smaller number of switches used in Vienna rectifier, and low switching frequency in MMC compared with conventional active rectifiers. The dynamic behaviour of the overall DC collection grid is also investigated in terms of (voltage/current) signal perturbations. The small-signal based control method which limits the signal variations to about zero is employed. Intensive simulations are presented with the use of the power simulator (PSim, Rockville, USA) software, to ride- through several DC and AC system faults.
