What is a power factor correction choke (PFC choke) and how does it work?

Question

They Exist

This Link at Newark displays "Power Factor Correction Chokes", which I did not know existed. I have a linear motor which I suspect really needs power factor correction. Please tell me what a PFC correction choke is, how it works, and more importantly, how I can tell which one to specify for my application.

Poor Explanations On-Line

The following links (What is a pfc?) and (Why are PFC chokes needed?) from Wurth were early hopefuls in trying to answer this question, but they were very disappointing, as their english was not very good, and their verbage not terribly elucidating. Why do the job half-way? You just make your company look bad, and I otherwise respect Wurth. Anyway...

Our Motor

Our linear motor directly connects to the line, at either 110v or 220v, I believe. I am really a software developer teaching myself power electronics, so I have some knowledge, but big gaps, I suspect. I entered pursuing this field through my love of a hobbyist circuit, a self-oscillating boost converter called the Joule Thief, so I am familiar with boost converters, which I recently found out here (EEsx why boost PFC topology is the most used?) are often the topology of a PFC correction circuit.

The motor is performing an actuation, and suspending a small weight, but then applies up to 15 kilograms of force, so varies in its power consumption from about 10 Watts to about 500 Watts. The current power factor seems to be about 30%, and gets much worse as greater force is applied. Some customers use our device constantly, and other customers use our device somewhat infrequently, so perhaps PFC could be an option?

Related to the Common Mode Choke?

Finally, In telling me what a PFC choke is, please tell me if and how it relates to the common-mode choke (which I believe has a different purpose). Thanks again.

Thanks

If buying one of these PFC chokes will improve efficiency for our customers, and deliver power to our motor more efficiently, I want to know. Thanks.

Edit #1

Though I may have indicated that this device needs help, it is actually in production, and working fairly well at customer locations. In some testing of the device I uncovered an obscure mode where the motor gets full power and then over temps -- but that's only with an administrative console and creatively power-cycling the controller+motor.

I really just want the questions in the Title answered.

In response to a question, "Must you replace the existing supply or improve it?" Improve, I think... Here is some more information that might help:

The linear motor controller is a Parker IPA15-HC, a SINGLE-AXIS SERVO DRIVE/CONTROLLER : 6.3A / 1*100-240VAC (2.5KVA) Links: 1. Brochure 2. Quick Ref Guide 3. HW install'n Guide

We wrote the firmware for the controller (in AcroBasic, a firmware Domain-Specific-Language specific to motor control). But the resource who wrote it may not be available, and I have only been at the company for 6 weeks.

Here is a first guess at the actual connections in the device, though the motor in the picture is rotary, and ours is linear -- this is a Basic connection diagram pulled from Hardware Installation Guide of IPA15-HC Servomotor Controller at URL 8:

Answer 1

A power factor correction choke (inductor) would be used to correct a leading power factor (current leads voltage) caused by a capacitive load. Your motor, being an inductive load, will have a lagging power factor (voltage leads current) and therefore its power factor should be corrected by adding a capacitor in parallel with it.

Edit. A power factor correction inductor can be added to a linear load (sine wave), which has a leading power factor, to increase the power factor. This type of power factor is known as a displacement power factor because the current is displaced relative to the voltage.

The other type of power factor is known as a distortion power factor where the power factor is neither leading nor lagging. This type of power factor can also be calculated from (real power)/(apparent power) but the concept of cos(phi), used for displacement power factor (sine wave and linear load), is no longer relevant. Distortion power factor being less than unity is caused by harmonic distortion introduced by the non linearization of the waveform due to, for example, a rectifier/capacitor input combination. The harmonics increase the reactive power. This type of low power factor can be improved by the addition of a front-end filter which removes the harmonics and therefore linearizes the load (current/voltage waveform). This harmonics reducing filter could be active or passive, the latter making use of inductors and capacitors.

Answer 2

Chokes do not correct power factor in the usual sense of "correcting" or the usual sense of "power factor."

Motors that are directly connected to mains power have a low power factor because they are inductive. To compensate or "correct" that, capacitors are used.

Loads that rectify and capacitively filter AC power, and other electronic circuits connected directly to mains power, have a distorted input AC current waveform rather than a smooth sine save current. That is harmonic current distortion. Harmonic current distortion has an effect that is similar to power factor. The RMS input current considering the distortion, is higher than an undistorted current would need to be to deliver the required power. Inductance (chokes) inserted in series with the input to such loads will reduce the distortion somewhat. Also harmonic filters can be designed using capacitors, resistors and inductors.

If your motors include electronic power conversion controllers, the controllers may need a harmonic reduction design. You can not simply select something and add it. However you could select series input inductors that cause 2.5% to 5% voltage drop at full load. That would provide some improvement. The typical impedance in the distribution system would provide close to the same improvement compared to a distribution system that has a very low impedance.

Improving power factor or reducing harmonics will not reduce the actual power used very much. It might even increase the power used. The only cost savings would be in avoiding a penalty that may or may not be charged for low power factor or harmonic distortion.

Answer 3

For the definition of the power factor you might have a look here. Ideally (power factor =1) the current of your load is in phase with voltage and is sinusoidal like a ideal resistor.

You can employ a special converter circuit (e.g. "active frontend") between grid and motor which shapes the current accordingly. A key component of such a converter would be the AC-side inductor of the converter.

In case of the simple diode rectifier, the converter's AC-side inductor would also improve the power factor, but not as good as in case of the active frontend.

A simple but very good illustration is shown here. Top, there is just a simple diode rectifier and the power factor is quite poor. Middle, there is a AC-side indcuctor added to the diode bridge rectifier which improves the power factor significantly (current shape is much more sinusoidal). Bottom, there would be a converter actively shaping the current and the power factor is 1.

A common mode choke blocks common mode current (the current going usually via capacitive coupling to ground) and works in the frequency range 150 kHz ... 30 MHz. The typical PFC choke is handling the differential current which is driven by the switching frequency of the converter.

It very much depends on the converter which is between the grid and the motor in order to figure out if a choke might help.