Resonance and its harmonic / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Resonance and its harmonic

1 2 next

Move Thread

LAN_403

Andy

Sun Jan 12 2014, 07:59AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi
I was wondering how to work out the harmonics of signals apart from bruteforce. If the 1st is 50hz, would the 2ns be 900hz.

Thanks

Proud Mary

Sun Jan 12 2014, 10:35AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Harmonics are sinusoidal voltages or currents that are whole multiples of a fundamental frequency at which a system is designed to operate.

A 150 Hz sine-wave signal, superposed onto the fundamental 50 Hz mains frequency, will be designated as the 3rd harmonic, also
called the harmonic of 3rd order i.e. 3 x 50 Hz.

The 2nd harmonic of 50Hz is 100Hz.

900Hz is the 18th harmonic of 50Hz. (900/50 = 18)

Andy

Sun Jan 12 2014, 05:58PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

When simulating it, the 18th and 72nd added to the voltage height, but the second etc hasn't. The circuit is transformers in parallel driving by different ac sources.

Why would the 18th and 72nd make a high voltage, but the others seem to not.

Proud Mary

Sun Jan 12 2014, 07:11PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Andy wrote ...

When simulating it, the 18th and 72nd added to the voltage height, but the second etc hasn't. The circuit is transformers in parallel driving by different ac sources.

Why would the 18th and 72nd make a high voltage, but the others seem to not.

I have no idea.

Andy

Sun Jan 12 2014, 07:41PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Thanks ProudMary

Below is the testing setup. I was just wondering if the harmonics added to the voltage, or weather its something else.

2Spoons

Mon Jan 13 2014, 01:49AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Try adding some realistic resistances (or any resistance for that matter). Modelling "perfect" components can lead to erroneous conclusions about the real world.

Mattski

Mon Jan 13 2014, 07:19PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

For a transient simulation you should also run it until it reaches steady state operation which it doesn't appear to have reached yet since the envelope of the signal is still changing over time.

Adding up a bunch of sine waves of a certain amplitude will get you a higher voltage than one sine wave of the same voltage, but the shape will depend on which harmonics and at what phase. Read up on fourier series to understand more.

You can also play around with sums of harmonics with Python or other programming scripting languages (I use PythonXY which comes with lots of bundled libraries), for example:

import numpy as np
import matplotlib.pyplot as plt
x = np.arange(0,1,.001)
f1 = 1
f2 = 2
y1 = sin(2*pi*f1*x)
y2 = sin(2*pi*f2*x)
ysum = y1+y2
plt.plot(x, y1, x, y2, x, ysum)

Another question is what are you trying to accomplish since I can't think of a good reason for combining a 50Hz wave with its 18th and 72nd harmonic. Is there a particular waveform you want to generate? Are you trying to get a high voltage?

Transformers are two-way streets so all of the different input signals will be coupled to all of the windings of the transformer and could affect the real-world AC voltage sources in wats that they don't affect ideal simulation sources.

Andy

Mon Jan 13 2014, 08:39PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Adding up a bunch of sine waves of a certain amplitude will get you a higher voltage than one sine wave of the same voltage, but the shape will depend on which harmonics and at what phase. Read up on fourier series to understand more.

Will do thanks.

I wasn't trying to generator any type of wave, just noticed that 1st,7th,18th,72nd would generator the power of two(I think, large jumps anyway), I was trying to get high voltages.The 50hz just matched line frequency that a coil and 12volt transformer would give off, with the pick up coils being the ac sources, not sure what effect that would have, maybe just two transformers in line?

Without the resistors it doesn't reach a steady state just makes about 0.05hz wave(tryed to make another block with 0.05hz frequnecy, but it doesn't make it go any higher), in that picture it peaked around 1.25mv, adding resistors it does have a climb then levels out around 10kv with 1ohm per block.

Andy

Wed Jan 15 2014, 03:18AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

I'm trying to get my head around something, I've read up about bandpass filters which the pic below shows, I was wondering if I have a 500khz frequency pass, can I amplifier the signal to 5volt> passively.

Dr. Slack

Wed Jan 15 2014, 09:24AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If by amplify, you mean add energy, ie not just change the voltage by changeing the impedance, and by passively, you mean with no energy source, then no, by definition.

You will tend to get more believable simulations if you add a sniff of series resistance to your coils. This has three benefits.

a) Simulators give silly answers if the solution matrix has no losses, as it becomes degenerate. Some will warn you, some won't.

b) Lossy inductors is more physical, you won't actually build any circuit with lossless ones.

c) A robust simulation will give substantially the same results as you vary the losses slightly. It's a good test of reasonableness to do. It allows you easily to find limits on the losses you can tolerate.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob