Fixed speed wind turbines always spin at the same speed regardless of wind speed, so their aerodynamic performance is only optimal at one wind speed. They use an induction generator directly connected to the power grid via a transformer to maintain a fixed frequency. Variable speed wind turbines allow the rotor speed to vary proportionally to wind speed between cut-in and rated speeds to maintain optimal aerodynamic performance through constant tip-speed ratio, and actively control torque above rated wind speed.

1. Solar and wind energy
Topic:- fixed and variable speed wind
turbine
by
Sonu kumar bairwa

2. Fixed speed wind turbine
• A fixed-speed wind turbine always spins at the
same generator/rotor speed during operation,
regardless of the wind speed.
• Thus, the tip-speed ratio (TSR) would change
with wind speed and the rotor aerodynamic
performance would only be optimal at a given
wind speed.
• The generator torque of a fixed-speed wind is
dictated solely by the induction generator.

3. • that the fixed-speed turbine actually has a
small variation in generator speed, so that
large variations in wind speed result in small
variations in generator speed and large
variations in torque / power i.e. the torque-
speed curve is steep.
• The power grid operates at a "fixed
frequency", so, coupling a fixed-speed turbine
to the grid is straightforward.
• Coupling a variable-speed turbine to the grid
requires a fancy power electronics i.e. AC-to-
DC-to-AC conversion

5. • FSWTs are equipped with an induction
generator (squirrel cage or wound rotor) that
is directly connected to the grid via a
transformer, with a soft-starter and a
capacitor bank for reducing reactive power
compensation.
• They are designed to achieve maximum
efficiency at one particular wind speed.
• In general, two control strategies have been
used with FSWT: Active stall control and pitch
control.

6. scSICG-squirrel cage induction generator
The connection with the grid is controlled by a soft-starter and a bank of capacitors.

7. variable speed wind turbine
• A variable-speed wind turbine allows the
generator/rotor speed to vary proportional to
wind speed between cut-in and rated speed,
thus maintaining a constant TSR and optimal
aerodynamic performance.
• Above rated speed, the generator/rotor speed
is then held constant. The torque must be
actively controlled.