Methods to make clean AC source

[steenge]

Hi All,

I need to do some standby-power measurements, in compliance to IEC 62301.

Therefore I must make sure that the AC supply used for the measurements meet these requirements:
1. Vrms = 230V +/- 1%
2. Freq=50 Hz +/- 1%
3. THC < 2%

Especially THC <2% (THD up to and including the 13.th harmonic) is really hard to get from the mains outlet.

My first thought was to look for a line conditioner, but as far as I can see, line-conditioners don't address THC.
Next thought was finding a pure-sine inverter, or an UPS, but Vrms is typically specified to +/- 3% and THC not even mentioned.

Any suggestions would be appreciated.

[Kleinstein]

One could use a function generator, audio amplifier, maybe coupling capacitor or DC adjustment and step up transformer.

The only difficulty can be getting a suitable transformer: One might to use two 230 V transformers in series or a 400 V one to get good linearity at lower magnetization. Even if only little power is needed, the transformers should not be less than about 10 VA, as small transformers are usually far from ideal.

For THD and the voltage you have to measure and maybe adjust the amplitude with the actual load - especially a bad nonlinear load could cause THD to increase.

[XFDDesign]

You don't specify any kind of loading, so if you can get loading to be a workable variable, I would suggest generating your 50Hz at a lower voltage, then apply passive LC filtering to kill any harmonics, take the output of the filter and step-it-up through a transformer to get your 230VAC_RMS, and apply an appropriate load to terminate the LC filter. It would be phyiscally large, but you can also control and measure how good it is.

[JFJ]

Any suggestions would be appreciated.

A programmable AC power source may meet your requirements, e.g:

http://www.newtons4th.com/products/laboratory-power-amplifiers/programmable-ac-power-sources/?gclid=CMjK6fS4wc8CFQUW0wodPW8OfA

http://www.mouser.co.uk/new/BK-Precision/bkprecision-9800-ac-power/ 

[bigsky]

I don't know how much power you need, but as a crazy idea, sig gen -> audio power amp -> step up transformer

A 60VRMS sine wave into an 8 ohm load is 450 watts, and audio amps of that rating are readily available

The transformer could be a mains one in reverse eg 230/30+30 rated at 450VA or so - like this one: www.rapidonline.com/vigortronix-vtx-146-500-130-500va-toroidal-transformer-230v-primary-2-x-30v-88-0006

Note that producing a continuous 50Hz signal at high power is a demanding task - I'd expect many amps not to be up it even if their specs suggested they could - they would either overheat or the power supply wouldn't be able to cope.

I'm not sure you'd need any filtering as hopefully the sig gen and amp would have a very low distortion figures. However, I don't know how much distortion the transformer would add.

[Jester]

Do a search for used Omicron, Manta Test, Doble  they make equipment for testing protective relays, they will generate 3 phase voltage and current.

[electr_peter]

Try TTI AC1000A Low Distortion 1kW Power Source (AIM AC1000A)
It provides very pure sine wave. Not sure about voltage stability to +/-1%, check datasheet.

[David Hess]

If you are doing this with a limited budget, then I agree with the other posters here about using a clean signal source to drive a big audio power amplifier with a transformer on the output.  Feedback from the output of the transformer can be used to reduce the output impedance to meet voltage stability requirements.

[_Wim_]

I wonder if a single phase VFD would be an option for you:

example: http://www.invertekdrives.com/variable-speed-drives/optidrive-e2-single-phase/specifications.aspx

These will create switching noise, but this noise will be above your 13th harmonic, so maybe this could be a viable option. VFDs can be found relative cheap on Ebay, although single phase output ones are not very common...

[steenge]

Tanks all for the interesting suggestions. I need this in my job, so for once I don't mind spending some dough!  Therefore I have chosen to go with the BK precision 9801, which seem to be a versatile instrument at a reasonable price (approx 2k EUR). Had it been for my own use, I would probably have gone for the audio amp+trafo solution.

[jitter]

Seems to me like it's a good choice given the specs...

Any chance of lifting the cover and taking some pics? 

[amirm]

I have been eyeing the BK unit for a while.

 Meanwhile, another option is audiophile products, the leader of which is PS Audio: http://www.psaudio.com/perfectwave-p5-power-plant/

I have one of their lower power units and its output is very clean.  It is a monster though (linear high voltage amplifier).

[oldway]

CVT (constant voltage transformer) with harmonics filter.