There are two types of grid connectivity
- Direct grid connection mean that the generator is connected directly to the (usually 3-phase) alternating current grid.
- Indirect grid connection means that the current from the turbine passes through a series of electric devices which adjust the current to match that of the grid. With an asynchronous generator this occurs automatically.
Grid Interfacing of a Wind Farm
Each wind turbine necessarily has individual connection of the power electronic grid interconnection to support the variable speed concept. The grid interconnection converts the variable frequency and magnitude outputs from the wind turbines to the synchronous frequency of the utility grid. The grid interconnection is consisted of 2 power converters, AC-DC and DC-AC converters. The grid interconnection decouples the voltages of the generators and the utility grid. The variable frequency and magnitude output voltages from the wind turbines are converted to DC voltages or so called DC links by the AC-DC converter. The grid side inverter converts the DC link voltages to the synchronous voltages of the grid.
There are three types of multi-level inverter.
- The first type is a diode clamped inverter. Each switching device of the diode clamped inverter blocks the voltage across one capacitor.
- The second type of the multi-level inverter is a flying capacitor inverter. Each switching device is clamped to one capacitor voltage level. This inverter requires a large number of bulky capacitors to clamp the voltages, similar to the diode-clamped inverter.
- The third type of the multi-level inverter is a cascaded full bridge or H-bridge inverter. The staircase waveform is synthesized by the full bridge converters connected in series.
