Adjustable Frequency Drive Harmonic Spectra 2

[dpc]

I'm looking for available test data on harmonic current distibrution on modern PWM drives (6 and 12 pulse)at various load points.

It's my (limited) understanding that the harmonic spectra can vary as a function of the drive load, so I'd expect different data at 20% load compared with 100% load.

Also, I'm curious if harmonic distribution is any different in fancier four-quadrant drives as opposed to simpler PWM drives.

My application for this is for use with some analysis software. We have some existing harmonic models for drives, but I'd like to get some addition data to verify.

What I'm looking for is harmonic current for each harmonic as a percent of the fundamental current.

Thanks.

 

[ScottyUK]

Hi dpc,

I haven't got any definitive data to pass on, but you are correct that the spectrum changes as the load increases. Assuming a straight rectifier front end, not a controlled bridge or active PFC type the following geenral changes will be observed:

At light load, the diodes conduct for a very short period, just maintaining charge on the DC bus reservoir capacitors. The very short pulse of current with steep rising and falling edges generates a spectrum with a high percentage content of high harmonics, although the overall current is low. The THD will be a fairly high percentage of the total current, although the total current will be low.

Fundamental current component will obviously increase as output power increases. Under heavy load, the diode conduction angle is broader and the capacitor ripple is larger. The lower harmonics around 5th and 7th will become dominant, and the high harmonics will become relatively small in amplitude. The THD as a percentage will be lower, although the actual values of the harmonic currents will be higher than the low-load condition.




-----------------------------------

Start each new day with a smile.

Get it over with.

 

[Skogsgurra]

...and keep that smile all day long...

dpc,

Scotty is very right in what he is saying. I have done a lot of those measurements over the years and there are files from FLUKE 41, Dranetz 4300, Fluke 199 and some other data collection "boxes". The drives measured are mostly Siemens, ABB, Danfoss and even a Lust - three-phase and some single-phase. There are some AFE inverters and also some CSI inverters, but that is probably not of any interest to you.

I can send them to you if you want them. Tell me how.

 

[dpc]

skogsgurra,

That would be great. I am mainly interested in PWM drives at this point.

You can e-mail me: esa06 "at" peak.org. If you have large files, I can provide you with ftp site info.

Many thanks,

dpc

 

[Skogsgurra]

will do

 

[jbartos]

Question: It is not clear from the original posting whether the sought function "harmonic content versus load" is on the VFD input side, VFD output side or both. Which one is it?

 

[ozmosis]

dpc, it does depend on the design and type of VSD you would look at. If you look at the 6-pulse drives then there is a huge difference between a 'standard' 6-pulse drive that has neither DC link chokes or AC line reactors and those that do. As a general rule of thumb you can say that a 6P VSD with no AC or DC reactors will contribute approx 60% THID, a VSD with an AC line reactor drops this to about 40% THID, A VSD with DC link reactor has about 35% THID. I work for Siemens and we have launched a 6P VSD(called the SED2) with special DC link design(with LHT..Low Harmonic Technology)that reduces the current harmonic distortion even further to about 30%. We have simulation software called HarmonEE that can show the effects of this and compare it to standards such as IEEE519.2, the UK G5/4 and other 'planning guidline' standards such as IEC 61000-3-6. It is about 10MB so maybe a little big to email through but let me know if you need it.
I have noticed recently that ABB have launched their new drive called ACS550 that has a 'swinging DC link choke'. There's not much data around on this but the claims made seem to point towards improvements of the typical DC link design.
On the subject of 12-pulse drives. Typically these will reduce significantly the 5th & 7th and the 17th/19th Harmonic orders to virtually zero. Worth looking at if the power rating is typically above 110kW(150HP) or so, as a rule. A number of companies provide software analysis of 12-pulse systems (Siemens, ABB, Control Techniques).

Note: as with any simulation program with Harmonics, it is the source data that is important and will always be different site by site depending on fault currents, supply impedance etc.

 

[jbartos]

Suggestion: Visit

http://www.mtecorp.com/mitigation.pdf

for:
Performance of Harmonic Mitigation Alternatives.
It is a good start.

 

[edison123]

jb,

That was an interesting article you've referred. I am starting another threas about this article.

btw, you get a star.

 

[Marke]

Hi dpc

Yes, the harmonic content is dependent on the load curent, it is also dependent on the supply impedance and the filter arrangements. Some drives do not include any inductors at all and these have the highest spectrum of harmonics. Others include DC Bus Chokes and the harmonic current relative to the rated load, is a function of the inductance of the DC Bus Choke and the capacitance of the capacitor bank. There is a value known as thew critical inductance for a given current and this has a bearing.
Additionally, there are drives that have a three phase reactor on the AC input and this also has a major affect on the harmonics.
If you are collecting information for cmparasons, it would probably pay to note the circuit characteristics as well, i.e. DC Bus choke, AC reactor, Supply impedance etc.

Best regards

Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Comment: Phase shifting transformers (also known as rectifier transformers, or isolation transformers) provide the harmonic mitigation plus galvanic isolation of the downstream VFD with motor with respect to upstream power distribution. Therefore, various ground currents are contained on the phase shifting transformer secondary side.

 

[jraef]

Marke,
I noticed that you have this thread marked for notification so I thought I'd post this here. Are you aware that we can't access your website (from the US at least). All I get is the following when I try:

http://hannah.aventurehost.net/suspended.page/

Sorry to others for being Off Topic.

"Venditori de oleum-vipera non vigere excordis populi"