[En-Nut-Discussion] 60Hz frequency measurment questions..

[Michael Jones]

Hello,

Are you measuring axis rotation speed or the actual frequency of the
generator output?

Generally I would suggest using a digital PID using the generator output as
reference. The PID would look a bit like:

	u(n) = u(n-1) + (Kv+Kp) Xd(n) + (Kn-Kp-2Kv) Xd(n-1) + Kv Xd(n-2)

Where:

	Kp = Kr (1 + Tv/Tn)
	Kv = Kr Tv/T 
	Kn = Kr T/Tn

	Xd(n): control deviation
	Kr: Amplificaion	
	Tn: Reset time
	Tv: Hold-back time
	T:  Samplerate

I have been using this formula for many projects and found it easy to apply
and implement. Though there is always the painfully time to find the correct
values for Kr, Tn and Tv. On some projects I did then add an extra
compensator that would level out temperature and (especially in your case)
other environmental factors. The Atmel easily has the resolution to count
the duration of every half wave and I would feed that directly into the PID.


Cu,
Michael

Btw: I loved reading your stereo mirror building articles... 


	

-----Original Message-----
From: en-nut-discussion-bounces at egnite.de
[mailto:en-nut-discussion-bounces at egnite.de] On Behalf Of James Lerch
Sent: Thursday, June 08, 2006 6:37 AM
To: en-nut-discussion at egnite.de
Subject: [En-Nut-Discussion] 60Hz frequency measurment questions..

Greetings All,

I'm going to use my EtherNut board as a engine monitoring and control system
for
my homebuilt 15KW generator project.  I think I've figured out how to
monitor
everything except the line frequency of the generator output (60hz ideally).

While the generator has a mechanical governor on it, it tends to sag about
1hz
between no-load and 60% load (10KW).  One goal for the Ethernut board is to
operate a governor assist system to help keep the generator producing 60hz
power
even under varying loads (else my UPSes all start getting upset).

The problem is I need to measure the frequency fairly accurately, preferably
in
the +/- 0.1% range, and be able to update the difference between real
frequency
and desired frequency fairly quickly. The diesel motor is a single
cylinder,running ideally at 1800rpm (15 power strokes per second, so I only
get
to measure few cycles of output to calculate the mean frequency, in time to
update the throttle position in time for the next power stroke)

Any thoughts or suggestions?

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating
site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge

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