Voltage Source Inverter Control for Variable speed wind generator

[Nathan K]

Hi Crew,
First post on here so I hope this isn't too specific.

I'm designing a sine wave inverter for a uni project and can't find a
good solution for controlling the voltage source inverter (half bridge).
Ideally it would have a sine wave generator (modulator -50Hz), carrier
(bipolar triangular - high freq) and comparator + bells and whistles
(current/temperature overload and low voltage cutoff).

I'm happy to make the circuit open-source if people are interested. It's
supposed to convert power from a variable speed wind generator (variable
speed, variable freq) into set voltage and freq for direct connection to
the grid.

Any suggestions, or pointers to resources appreciated.

Cheers,

Nathan

 

[Nathan K]

Isn't the usual way to do a wind turbine to run an induction generator at
constant speed plus slip? An induction generator is essentially an induction
motor excited by the mains but driven higher than synchronous speed by
geared wind torque from the prop. An induction motor becomes a generator
when mechanically driven at a speed higher than the synchronous speed. It
then delivers power into the mains instead of taking power as it does when
used as a motor. The frequency is the same as the mains and controlled by
them. The waveform is sinusoidal as in other rotating machinery.

The local controller controls the prop pitch and adjusts the blades to keep
the slip speed and thus the torque in bounds. A cutout is used to keep
generator from motoring in low wind velocity. The blades are feathered and
locked when the wind is out of bounds, too high or too low.

Such a scheme doesn't require an inverter or other high power electronics.

True. But it is probably less efficient. In order to assert this I need
to design and optimise a system to see what type of efficiency I can
get. Variable speed is more efficient because it is possible to optimise
the RPM to maximum torque. This is done by adjusting the load as seen
from the wind generator via PWM. It is also possible to feedback energy
at lower wind speeds, when Vout is below the grid level. This is done
with a boost PWM.