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pf correction w/battery bank inverter


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#1 bobg

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Posted 09 March 2004 - 08:22 AM

just found your board and look forward to learning all i can from you guys.

my question is one of power factor correction, under the following criteria

1. off grid home

2. battery bank 12 volt dc storage

3. modified square wave inverters, aka modified sine wave

in reading on the subject of power factor correction i understand it is not common practice on residential installation as the power companies dont offset or penalize for low power factor.

when considering generating ones own power, with the related battery storage and inverters to convert to 120vac, the subject of power factor correction comes to mind to improve the overall efficiency of the system, ie. less battery draw, longer life, and smaller inverter sizing.

all i read re: inverter useage is that it is a no no, but it would appear that is in relation to inverters used that are supplied by the power utility and not batteries.

the references say not to use caps on the input side of an inverter because of amplified line surges etc, on a dc battery system one wouldnt use caps there anyway.

they also reference problems in using caps on the output side of inverters, and here again i assume they are still in reference to ac mains inverter for speed control etc. and not the battery powered inverters..

bottom line is can i use power factor correction on dc powered inverter systems at the motors? if i use contactors to isolate the inverter from the caps, and the caps from the motor?

when one considers becoming his own power company, efficiency is definetly the key to success.

any help here?

thanks for you time

bob g

#2 marke

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Posted 09 March 2004 - 09:10 AM

Hello bobg

I would not apply power factor correction to the output of an inverter unless the following are ensured:


  • The output voltage of the inverter is a pure sine wave. - no distortion
  • The inverter manufacturer is happy to have power factor correction connected to the output of the inverter.

      If the voltage waveform applied to the inverter is not a pure sinewave, there will be significant harmonic currents flowing and these will damage the capacitors unless suitable filters are connected.
      Connecting capacitors on the output of an inverter will result in very high transient and switching currents within the inverter and these can lead to damage to the inverter.

      Sorry, but I would not recommend the connection of PF correction without consulting the inverter supplier and ensuring that any warantee would be honoured.

      Best regards,

#3 Pajjen

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Posted 15 August 2007 - 07:55 AM

QUOTE(marke @ Mar 9 2004, 09:10 AM) View Post

Hello bobg
I would not apply power factor correction to the output of an inverter unless the following are ensured:
[list]
[*]The output voltage of the inverter is a pure sine wave. - no distortion
[*]The inverter manufacturer is happy to have power factor correction connected to the output of the inverter.
[list]
If the voltage waveform applied to the inverter is not a pure sinewave, there will be significant harmonic currents flowing and these will damage the capacitors unless suitable filters are connected.
Connecting capacitors on the output of an inverter will result in very high transient and switching currents within the inverter and these can lead to damage to the inverter.
Sorry, but I would not recommend the connection of PF correction without consulting the inverter supplier and ensuring that any warantee would be honoured.
Best regards,


Hello, im a new member on the forum and i have difficulties to find litterature and papers relating to my problem. The statement made by marke above is that you should not apply power factor correction to the output of an inverter unless it is an pure sinus and that there is no distortion.

I have read this on one other source to http://www.lmphotoni...ct.htm#inverter. But i want to read more and understan why this is so.

I have been experimenting with a system to connect between mains and an inductive load. The system contains of EMI filter -> Active pfc circuit -> flyback converter -> inverter -> load, The output is an squarewave.

My problem is that the load is internaly compensated with an 12uF condencer and i donīt want to tear it appart to dissconnect the condencer. I have tested this and it gives me an PF = 0,40 at 90W 230VAC load, the values are measured with an MetraHit 29s and i belive are quite accurate (it is a True RMS meter). With the condencer connected the strain on the inverter is to big (blown fuse and mosfets).

What i want is to know if there is any more information written about the difficulties with capacitive load on the output of an inverter and if there is any way to compencate the capacitive load generated buy the built in capacitance.

Is it possible to compencate buy creating an resonant circuit buy adding an parallell inductor matched to the capacitance?

//Pajjen

#4 marke

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Posted 19 August 2007 - 01:41 AM

Hello Pajjen

If you add capacitors to the output of switching devices, there will be very high charging currents through the switching devices and the capacitors. This current will only be limited by the circuit impedance as at the point of switch ON, the capacitors will look like a short circuit. If you have any inductance in the system, the capacitance and inductance will for a resonant circuit and so you can also get very high ringing voltages in addition to the charge/discharge currents.
If you can limit the rate of rise of current and /or voltage at the output of the inverter, the problem will be reduced. The best means of doing this is to apply a sinusoidal filter between the output of the inverter and the load. This can be quite an expensive exercise.
The best answer is to avoid switching into capacitive loads.

Best regards,




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