DC converter's power factor.

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Chelny

Chelny

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Russia
Hello everyone,

I'm interested in some theory on following questions:

  • if DC converters worsen power factor;
  • power factor dependency on speed of DC motor;
  • please guide me to the documents on this topic;

thanks in advance

Chelny
 
Jraef

Jraef

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Electrical Engineer
Chelny said:
Hello everyone,

I'm interested in some theory on following questions:

  • if DC converters worsen power factor;
  • power factor dependency on speed of DC motor;
  • please guide me to the documents on this topic;

thanks in advance

Chelny
Click to expand...
Worsens compared to what? DC converters can be made in many different ways and what type you use will have an effect on the power factor it presents to the line. Some will have less of a displacement power factor and more of a distortion power factor, others will be the opposite.

It will not likely change with loading of the DC motor with regard to the % power factor, but the AMOUNT of VARs involved will change.

Documents will again depend on what your converter is.
 
jumper

jumper

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Found an interesting paper.

Wonder if it kinda answers OPs question. I know I am gonna read it.

A Single Phase Single Stage AC/DC Converter with High Input Power Factor and Tight Output Voltage Regulation
A. K. Jha
Birla Instt. of Technology, India
B. G. Fernandes and A. Kishore
Indian Institute of Technology, India
Abstract—A single stage single switch AC/DC converter is an integration of input current shaper and a DC/DC cell with a shared controller and one active switch. The converter is applicable for digital input power supply with high input power factor and tight output voltage regulation. The focus of the topology is to reduce the DC bus voltage at light load without compromising with input power factor and voltage regulation. The concept behind this topology is direct power transfer scheme. Using special configuration of DC/DC cell does reduction of DC bus voltage and DC/DC cell works on the principle of series charging and parallel discharging. The power output of this converter can go up to 200 W.
 
junkhound

junkhound

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EE, power electronics specialty
  • if DC converters worsen power factor; If straight rectifier, yes, if PFC circuit no
here is a starting place for you. The 'offline' is the key work, search for 'offline PFC circuits', hits such as:
http://www.ti.com/power-management/...rs-converters/factor-correction/overview.html


  • power factor dependency on speed of DC motor;
see above


  • please guide me to the documents on this topic;
search for "Vienna bridge" for some of the latest PFC AC-DC converter circuit types.

 
I

Ingenieur

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Earth
I looked at a few 480/3 : 500 dc Seimens drives 300-700 hp range

output rated power armature + field / input power for the same
divided that by eff
the result should be pf
the range was ~0.78-0.82

on drives ~100 hp improves to 0.86-0.90 range
 
Last edited:
Chelny

Chelny

Member
Location
Russia
Ingenieur said:
I looked at a few 480/3 : 500 dc Seimens drives 300-700 hp range

output rated power armature + field / input power for the same
divided that by eff
the result should be pf
the range was ~0.78-0.82

on drives ~100 hp improves to 0.86-0.90 range
Click to expand...

Glad to see you continued your help.

Currently looking at Simoreg document e.g., 3AC, 400V, 210-600A, Q1, page 3-8, and I found nothing:


  • about eff itself;
  • input power;


I found only:

  • rated output (KWt). I don't know if here is general rated output (armature+field) written;
  • power losses (Wt);


So, could you guide me where I can find the 'unknowns' of your equation?
Here is a link to Simoreg document I reffered: https://support.industry.siemens.com/cs/document/22220212/simoreg-dc-master-6ra70-software-version-3-1?dti=0&lc=en-WW



 
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Jraef

Jraef

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Power factor is an AC phenomenon, so what happens on the motor side is irrelevant.

Power factor on the rectifier side is mostly distortion power factor and will not change much with load on the motor. It MIGHT change from one drive to another based on the stiffness of the system feeding it though. A 100kW drive fed by a 100kVA transformer will have a LOT more distortion that a 100kW drive fed by a 1000kVA transformer.
 
I

Ingenieur

Senior Member
Location
Earth
using the size 75 as an example

input i = 175 A (think this incleds field and armature)
output power = 88 kw
losses 0.676 kw

calculate eff
eff = output dc pwr/(putput dc pwr + losses+ fan + controls)
= 88/(88 + 0.676 + ignore fan + 0.38) = 0.988

calculate input power
Pin = (sqrt3 x 175 x 400) + 380 (controls) = 121.6 kva

pf = 88/121.6/0.988 = 0.73
 
Last edited:
I

Ingenieur

Senior Member
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Earth
the field is powered seperately 400/1
so add it to Pin, and consider it a 'loss'
P = 15 A x 325 dc = 5 kw
P in ~ 7 kva (assuming a pf x eff ~ 0.7)

eff ~ 88/(88 + 5 + 0.676 + 0.38) = 0.94 (ignore fan)
Pin = 121 + 7 + 0.380 = 128.4 kva

pf = 88/128.4/0.94 = 0.73

same as before
 
Chelny

Chelny

Member
Location
Russia
Jraef said:
Power factor is an AC phenomenon, so what happens on the motor side is irrelevant.
Click to expand...
Yes, it's wide known and proven fact that PF has nothing to do with DC current.

Jraef said:
Power factor on the rectifier side is mostly distortion power factor and will not change much with load on the motor. It MIGHT change from one drive to another based on the stiffness of the system feeding it though. A 100kW drive fed by a 100kVA transformer will have a LOT more distortion that a 100kW drive fed by a 1000kVA transformer.
Click to expand...

I don't think so.

That's what the guys from ABB are saying in their work. See attachment. Unfortunately I failed to upload here entire file. https://www.google.com/url?sa=t&rct...+Release.pdf&usg=AOvVaw1z1TES5EnSQ07qPasU_OoU
It is shown the magenta line looks particularly bad, especially at low motor speed range. :?
To prevent this bad thing most dc drive's manufactures resort to the different techniques which common name is PFC (power factor correction). So I would like to know how much advanced SIMOREGs on this theme (Siemens still said nothing) and as you could see in tech docs, there is no word about PF. :?
So I'm looking for ways on finding out more or less exact PF values.


@Ingenieur,
calculated 0,73 is pretty bad in contrast with AC Drives. Isn't it? Your opinion?
Also it's proved by ABB guys in their work.

thank you very much for your explanation. :thumbsup:

Chelny
 

Attachments

  • PF_comparison_btw_AC_DC_drives_Optimized.pdf
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Last edited:
Chelny

Chelny

Member
Location
Russia
I'm sorry,

Is it typo? I can't find 88 kw in size 75 specification. How have you got that value? I've only found rated output 102 KW. I'm reffering to a link I posted above.

using the size 75 as an example

input i = 175 A (think this incleds field and armature) (found);
output power = 88 kw (not found);
losses 0.676 kw (found);
Click to expand...

Chelny
 
Chelny

Chelny

Member
Location
Russia
and why controls consume 0.38 KW? From where have got that value?

calculate eff
eff = output dc pwr/(putput dc pwr + losses+ fan + controls)
= 88/(88 + 0.676 + ignore fan + 0.38) = 0.988
Click to expand...

Chelny
 
I

Ingenieur

Senior Member
Location
Earth
Chelny said:
Glad to see you continued your help.

Currently looking at Simoreg document e.g., 3AC, 400V, 210-600A, Q1, page 3-8, and I found nothing:


  • about eff itself;
  • input power;


I found only:

  • rated output (KWt). I don't know if here is general rated output (armature+field) written;
  • power losses (Wt);


So, could you guide me where I can find the 'unknowns' of your equation?
Here is a link to Simoreg document I reffered: https://support.industry.siemens.com/cs/document/22220212/simoreg-dc-master-6ra70-software-version-3-1?dti=0&lc=en-WW
Click to expand...

must have mixed them up, correct 102 kw (using an iphone lol)

from chart 3.4.3
rated V for electroncs 380 V min x 1 A = 0.380 va
at the bottom of the chart it states losses at rated output 676 w
fld 16 x 325 = 5.2 kw or ~ 6.7 kva

eff = 102/(102+5.2+0.676+0.38) = 0.94

Pin = 175 x400 x sqrt3 + 6.7 + 0.38 = 128.3

pf = 102/128.3/0.94 = 0.85
 
Besoeker

Besoeker

Senior Member
Location
UK
Ingenieur said:
I looked at a few 480/3 : 500 dc Seimens drives 300-700 hp range

output rated power armature + field / input power for the same
divided that by eff
the result should be pf
the range was ~0.78-0.82

on drives ~100 hp improves to 0.86-0.90 range
Click to expand...
Possibly so if the figures are for for rated max operational speed.
But PF greatly depends on the speed. And it is probable that a DC drive would be used for variable speed applications.

On a paper machine for example* with a maximum line speed of 1000 mpm, the crawl speed is normally in the 10 mpm range.
BIG BIG difference in PF of course.

Assuming six-pulse rectification, max DC output voltage is 1.35 Vac at a PF of 0.958. But, you need to build in a control margin so you are down to around your 0.82 at maximum design speed. And lower if you operate below that.

I'm just expanding on your information in the hope that it may be useful to the OP.

*Paper (making) machines were the biggest market segment for our DC drives. Quite a demanding application.
 
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