Quote:
Originally Posted by xelasnave
Yes thanks for posting Gary.
I was surprised as to how efficient a well designed flywheel is and how its ability to store energy is, as I recall and sorry for no referenced authority other than my most unreliable memory, to be superior to a battery.
What type of battery of course but the thought of a flywheel spinning away for an extended period and losing less energy than a battery really surprised me.
Their potential to run around and do damage had not occurred to me.
Alex
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Hi Alex,
The synthetic inertia systems on wind turbines discussed by the authors
don't employ a separate flywheel.
Instead they use the mechanical inertia of the wind turbine itself coupled
with control systems added to the power electronics.
By way of background, historically, power generation by steam turbines
uses synchronous generators. That is, the rotational speed of the generator
is synchronous with respect the (here in Australia) 50Hz alternating
current of the grid.
As wind turbine technology has evolved, rather than connect their generators
directly to the grid, the trend has been to employ power electronics that
go between its generator and the grid.
This has been made possible by huge advances in power electronics
over the past thirty or forty years.
For example, some systems employ double converters that convert the
AC from the wind generator to DC and another converter that converts
that DC back to (50Hz in Australia) AC which is synchronized with the
grid.
There are additional closed-loop control systems that feedback from the
grid back to the converters and to the turbine itself.
Power grid systems and power integrity on a grid is surprisingly complex.
Rather than there being just an alternating voltage waveform there is
also an alternating current waveform. Since power is the product of
voltage and current, on the one hand, ideally the two waveforms would be in
phase to deliver maximum power to a load. This is referred to as unity
power factor. When voltage and current is not in phase it is referred to
as reactive power. However, some amount of reactive power is required for
some motors to operate and reactive power plays an important role
in maintaining the voltage on the grid. It is a careful balancing act
between the amounts of normal power and reactive power on the grid.
Ideally the generators on the grid should be able to produce or
absorb reactive power to or from the grid itself.
So the synthetic inertia technology, which has been evolving in recent
years, is a combination of the inertial mass of the rotating machinery,
the power electronics conversions and the control systems used in
the feedback loops.
Control systems in (electrical) engineering is a complex area in itself with
deep roots in mathematics. That is also true literally as many control
systems utilize the mathematics of matrices of complex numbers
(electrical engineers love using complex numbers, that is, where the
square root of -1 is defined as the complex number "i" but electrical
engineers prefer to denote with the letter "j" because we already use "i" to
denote current).
We have had over 100 years experience in designing power distribution
systems using synchronous rotating machines. With the advent of
renewable power sources whose inherent generation schemes may
be asynchronous and even DC, there is less experience to draw upon
but many talented professionals are evolving the field quickly.
For example, the advances in semiconductors used in power electronics
continues to rapidly advance.
There was the famous debate between Edison and Tesla
on DC versus AC. Rotating machinery and passive transformers made
the obvious choice based on the technology available at the time.
Based on the technology available today, the debate would probably be
even harder fought if we were starting afresh.
