Building voltage regulator for induction generator

[AlanBown]

Hi

Please can somebody tell me the easiest way to control the voltage output of
induction generator.

The generator is three phase 11 kW, excitet by capacitor bank of 240 µF; as
a prime mover a tractor of 30 HP has been used. The speed of the generator
can manually be adjusted, but when done, then the speed is more or less
constant.

The problem is that the output voltage depends greatly on the induction
generator speed and load. For a given capacitor value, self-excitation can
only be achieved and maintained under certain load and speed combinations.
The machine demagnetizes and stops generating either when the speed falls
bellow, or the load rises beyond certain values.

Your description above indicates to me that your looking for something that
can not be easily done. Every generator control I have ever dealt with has
the ability to increase speed as the load increases. Since your doing this
manually I see problems. Have you considered the frequency issue as well?
As load increases and the speed stays the same voltage and frequency would
fall.
http://www.flightsystems.com/electronic_generator_controls/

http://www.controlsinc.com/controls.asp

I hope these pages from google help your process

 

[Silvek]

Hi

Please can somebody tell me the easiest way to control the voltage output of
induction generator.

The generator is three phase 11 kW, excitet by capacitor bank of 240 µF; as
a prime mover a tractor of 30 HP has been used. The speed of the generator
can manually be adjusted, but when done, then the speed is more or less
constant.

The problem is that the output voltage depends greatly on the induction
generator speed and load. For a given capacitor value, self-excitation can
only be achieved and maintained under certain load and speed combinations.
The machine demagnetizes and stops generating either when the speed falls
bellow, or the load rises beyond certain values.

So plese can somebody help me solve this problem. I would like to build
voltage regulator for IG that maintains stabile voltage regardless of load
and speed value.

I have looked for this topic on the internet, but i found only very
complicated solutions which included voltage source inverters, and digital
controllers based on a Pentium PC.
I dont have anything against voltage source inverters or something similar,
but hooking up a PC to control the voltage output is a bit to much.

Any ideas would be greatly appreciated; the simpler the better, even if the
voltage regulation itself is not 100% accurate, as long as i can avoid
demagnetization and regulate the output voltage.

Thanks.

 

[Big John]

Hi Silvek,

Controlling the output voltage of an induction generator is not easy. In
a regular alternator, the speed of the prime mover is kept constant to
maintain a fixed frequency and the output voltage is adjusted by changing
the alternator's field current which changes the strength of the magnetic
field. You can't do this with an induction generator.

I do know a way to control the output voltage, but it isn't the best
solution. First, as with a regular alternator you want to keep the prime
mover's speed constant to maintain a constant frequency. Next, you want to
fool the induction generator into thinking that it has a constant load no
matter what the actual load is. The way to do it is called load diversion
regulation or shunt regulation. The way it works is a large resistive load
(like say an electric hot water heater) is connected to the generator using
something that can vary the amount of power. SCRs can be used for this.
The regulator senses output voltage. If it's too high more of the
generator's output power is sent to the load. If the voltage is too low
less power is sent to the load.

This type of regulator can be made with basic analog control components
like op amps. With some SCR's and a large resistive load you can easily
control 11 KW. Shunt regulation can also react quickly to load changes, but
there are some problems. First, any power you are not using is sent to the
load - which is terribly inefficient unless you are usually running near
full load most of the time. The resistive load converts everything not
being used to heat. Great if you need a lot of hot water or you wanted to
heat a construction site anyway. Not so great if things are already too hot
where you are running this generator. Also, what you use for a resistive
load must be reliable - if not a sudden loss of load will cause the voltage
to shoot up and damage anything connected to it. So regular light bulbs
that burn out are not a good idea.

This type of regulator is often used on small hydrogenerators. So if you
want more info try doing a google search on small scale hydro power and load
diversion / shunt regulator.

Hope this helps,
Big John