Talk:Variable-frequency drive

From Wikipedia, the free encyclopedia

WikiProject Systems
Systems science Portal
This article is within the scope of WikiProject Systems, which collaborates on articles related to Systems science.
Systems rating: Start Class Mid importance  Field: Control theory
Please update this rating as the article progresses, or if the rating is inaccurate. Please also add comments to suggest improvements to the article.

Contents

[edit] Operating principle

I changed f rom RPM = {{{120 \times f}\over{p}}} TO RPM = {{{60 \times f}\over{p}}} I'm right? Minute has 60 seconds, ferquency is in Hz, so it is natural to multiplie with 60 not with 120, as is stated p is Number of pole pairs, not number of poles!

Variable frequency drives operate under the principle that the synchronous speed of an AC motor is determined by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:

   RPM = {{{60 \times f}\over{p}}}

where

RPM = Revolutions per minute

f = AC power frequency (hertz)

p = Number of pole pairs(an even number)

Synchronous motors operate at the synchronous speed determined by the above equation. The speed of an induction motor is slightly less than the synchronous speed.

The above unsigned material is technically correct except that the number of pole pairs can be either an even or odd number. The previous persentation was also technically correct and, I believe, the more usual way that the material is presented. I have several USA references including that state the poles in an AC motor as poles rather than pole pairs. Is "pole pairs" the more common usage elsewhere? -- C J Cowie (talk) 15:40, 26 March 2008 (UTC)
Reference re use of "poles" vs. "pole pairs": NEMA Standards Publication (2002). Information Guide for General Purpose Industrial AC Small and Medium Squirrel-Cage Induction Motor Standards (Condensed MG 1-2002). Rosslyn, VA USA: National Electrical Manufacturers Association. Retrieved on 2008-03-26.  -- C J Cowie (talk) 17:58, 26 March 2008 (UTC)
The following references support the previous presentation of this material:
  • Campbell, Sylvester J. (1987). Solid-State AC Motor Controls. New York: Marcel Dekker, Inc., p86. ISBN 0-8247-7728-X. 
  • Fitzgerald, A. E.; Kingsley, Charles Jr. and Umans, Stephen D. (1983). Electric Machinery, 4th ed., Mc-Graw-Hill, Inc., p122. ISBN 0-07-021145-0. 
  • Gehmlich, Dietrich K.; Hammond, Seymour B. (1967). Electromechanical Systems. Mc-Graw-Hill, Inc., p296. 
  • Siskind, Charles S. (1963). Electrical Control Systems in Industry. New York: McGraw-Hill, Inc., p223. ISBN 0070577463. 
  • Smith, Ralph. J. (1971). Circuits Devices and Systems, 2nd ed., John Wiley & Sons, Inc., p574. ISBN 0-471-80170-4. 
C J Cowie (talk) 23:07, 26 March 2008 (UTC)
Unless a good rationalization and references are provided for the current version, I will revert this section to the previous version and add the references cited above. --C J Cowie (talk) 23:18, 26 March 2008 (UTC)

I agree: "I believe, the more usual way that the material is presented. I have several USA references including that state the poles in an AC motor as poles rather than pole pairs. Is "pole pairs" the more common usage elsewhere?" My personal expirience is that severeal european university are using pole pairs, but for USA references is more common use of poles. I'm living decision to You, but mayby difference should be stated somewhere in the page becouse of european students? —Preceding unsigned comment added by 89.188.39.77 (talk) 12:53, 27 March 2008 (UTC)

[edit] Braking

My understanding is that there is a way to also use a controller like this to brake a motor by purposefully lagging the phases but it is not clear to me what the power-take-off circuit looks like in this case. Can anyone explain how regenerative breaking works in conjunction with this type of controller? —Preceding unsigned comment added by Laughingskeptic (talk • contribs) 18:03, 24 November 2007 (UTC)

When the frequency is reduced more quickly than the motor will coast down, the synchronous speed drops below the operating speed and the inherent characteristics of the motor cause it to regenerate. The power returns to the DC bus through the anti-parallel diodes in the inverter circuit. If the regenerative energy is not removed, the DC bus capacitors will charge to an excessive voltage level. Standard VFDs monitor the bus voltage and limit the rate of frequency reduction to prevent excessive regeneration. There is also a DC overvoltage trip feature that will shut down the VFD if the voltage gets too high. It is also possible to switch resistors across the DC bus for dynamic braking or return the energy to the AC line for regenerative braking. The energy is returned to the AC line using a regenerative AC to DC converter circuit. -- C J Cowie (talk) 19:19, 24 November 2007 (UTC)

[edit] Regeneration

There really should be something about regenerative braking in the main article. Cowie, can you do it? --Treekids 20:18, 4 December 2007 (UTC)

[edit] LIMs

Linear motors also use VFDs. Operating principles does not seem to cover these.

[edit] Attention?

An anonymous editor just added the "Attention" template (well, sorta kinda) and the following text:

Full speed listing:
After the initial acceleration to full speed a 2-pole synchronous motor connected to a power supply that operates at 50 Hertz (cycles per seconds) runs at 3000 revolutions per minute (RPM). If 4-poles then 1500 RPM, if 8 poles then 750 RPM, etc.
After the initial acceleration to full speed a 2-pole synchronous motor connected to a power supply that operates at 60 Hertz (cycles per seconds) runs at 3600 revolutions per minute (RPM). If 4-poles then 1800 RPM, if 8 poles then 900 RPM, etc.
As the frequency of the power supply is changed, the motor's final speed is changed accordingly.

Until they added that text, I though the article was pretty fine, albeit a bit short. Now, I definitely agree that it needs "attention".

Does anyone feel strongly that this new text shouldn't be deleted (it's more relevant to Electric motor and the "attention" sorta-kinda template removed?

Atlant 17:17, 17 July 2005 (UTC)

exactly -vega007

I deleted the "attention" but left the "full speed listing" although I think the substance of it is covered under Electric motor. I would like to give this much more attention, but this is my first day. I am working on a more general article on adjustable speed drives. C J Cowie

I say loose it. It's a description of what motors do under various frequencies. VFDs certainly provide motors with variable frequency, but this article isn't about describing how things operate when connected to a VFD. Plus, the text is non-encyclopedic. Mainstreetmark 18:38, 27 October 2005 (UTC)
Although the article isn't about describing how a motor operates when connected to a VFD, the motor performance is part of the underlying principles of VFD operation. I expanded the article with that in mind. I have more material that I will add later.

Capacitor symbol polarity appears to be reversed in the PWM_VFD_Diagram.PNG image. The '+' symbol at the bus rail doesn't conform with the direction of the capacitor symbol (the 'flat' side should be towards '+'). Zootsuite 01:25, 14 May 2007 (UTC)

I have corrected the diagram, thank you. C J Cowie 14:52, 14 May 2007 (UTC)

[edit] ratings of devices not given.

[edit] Re VFD Motors

There are problems with the bolded addition to the following sentence: Various types of synchronous motors offer advantages in some situations, such as the use of hall sensors to control inverter frequency and pole switching to vary the frequency to rotational speed ratio, but induction motors are suitable for most purposes and are generally the most economical choice. The use of hall sensors in VFDs is generally not related to the type of motor used. Hall sensors are used in VFD circuits for current sensing and as one of several types of shaft speed and position sensor. Pole switching is a means of changing the operating speed of an AC motor, but it is generally not used in conjunction with variable frequency drives. --C J Cowie 18:07, 12 March 2006 (UTC)

[edit] Servomotor article needed

An article on servomotors, linking to this article and to "brushless DC" motors, would be useful, to fill out the area of motor control.

It's worth mentioning that "brushless DC" motors are really synchronous AC motors, and need a variable frequency drive. For historical reasons, small brushless servomotors are referred to as "brushless DC", and larger ones (1KW and up, typically) are referred to as AC motors. Brush-type DC motors, on the other hand, take a DC input.

[edit] Newer control methods

There are newer variations on PWM control method. The standard method uses an image of the motor characteristic and pulses the frequency accordingly. Latest methods use Direct Torque Control and control the pulse width by reading the feedback from the motor. This enables individual phases to be pulsed more accurately and accounts for correction of imbalances prevalent in actual motor windings. Aroonl 03:48, 31 January 2007 (UTC)

[edit] Line and load reactors

I was wondering if we should include a section on line and load reactors and their use with VFDs. Is this common practice everywhere, or just for certain industries/regions/manufacturers? --W0lfie 19:04, 15 March 2007 (UTC)

Line and load reactors are not always needed. If the VFDs don't make up too large a percentage of the connected load, harmonic distortion of the input current and voltage may not exceed acceptable levels without input reactors. If the motor is constructed to withstand high voltage spikes and dv/dt and/or is close to the VFD, load reactors may not be necessary. In addition, built-in drive features may reduce the need for external input and/or output reactors. Also, Wikipedia is not supposed to be an instruction manual. A full discussion of the proper application, installation and operation of VFDs is likely beyond the intended scope of a Wikipedia article. C J Cowie 19:21, 15 March 2007 (UTC)
I agree, it's probably not in the scope of the encyclopedia if it's not universal. That's why I asked. It's pretty common in my industry, but I didn't want to change the article if it wasn't representative of all VFD installations. --W0lfie 02:28, 25 April 2007 (UTC)

[edit] Cable requirements

Also, I read somewhere that you should use shielded 1000V cable between the VFD and the motor. [1] for instance. Is that true? I haven't ever noticed any problems running regular unshielded 600V cable out to the motors. I couldn't find anything in the NEC at all about VFDs. --W0lfie 19:04, 15 March 2007 (UTC)

Article 430 of the 2005 National Electrical Code has a new section on Adjustable-Speed Drive Systems:
X. Adjustable-Speed Drive Systems
430.120 General. The installation provisions of Part I through Part IX are applicable unless modified or supplemented by Part X.
This section contains provisions: calling for branch/feeder conductor sizing for not less than 125% of the rated input current of the drive, permitting the drive to provide overload protection for the motor, and permitting the disconnecting means to be in the incoming lines to the drive and rated for not less than 115% of the rated input current of the drive.
Many if not most VFD manufacturer's instructions indicate that shielded motor cable is required to meet the EMI requirements of the European area. I know of at least one IEEE paper that discusses shielded motor cable and I believe recommends using it in some circumstances. I am pretty sure that John Bentley is one of the authors. C J Cowie 19:32, 15 March 2007 (UTC)
The IEEE paper is: Evaluation of motor power cables for PWM AC drives; Bentley, J.M.; Link, P.J.; Industry Applications, IEEE Transactions on, Vol.33, Iss.2, Mar/Apr 1997, Pages:342-358. It includes a discussion of insulation voltage ratings. C J Cowie 20:01, 15 March 2007 (UTC)

[edit] Uses?

This is an interesting page from an engineering standpoint, but perhaps someone could add a few sentences about what they're actually used for? —Preceding unsigned comment added by 204.11.6.125 (talk) 19:09, 28 September 2007 (UTC)

For uses, see Adjustable-speed drive. C J Cowie 22:23, 28 September 2007 (UTC)

Uses! Its everywhere. Patricularly in industries to control speed of machines [Sandeep Poddar] —Preceding unsigned comment added by 59.89.48.60 (talk) 02:38, 18 October 2007 (UTC)

Might I ask, can the vfd or similar be used for power generation? Is this used in hybrid cars? Wind energy generation? —Preceding unsigned comment added by 209.242.238.145 (talk) 21:16, 15 November 2007 (UTC)

VFDs are one option for controlling an electric motor(s) in a hybrid or electric car. I believe that there are some manufacturers presently using that approach. They have also been used in much larger electric vehicles such as electric railway locomotives. Some wind energy schemes use an induction motor controlled by a VFD as a generator. DC power from the VFD is passed to the grid using an inverter. C J Cowie 23:19, 15 November 2007 (UTC)

[edit] Links to Related Articles

I've tried to post external links to three variable frequency drive articles that could really be a great research resource. For some strange reason, they will not post, and it's not from a lack of trying. I've posted them about 5 times. The links are as follows:

Article 1: The Benefits of Variable Frequency Drives - This article outlines the energy savings, the tighter process control, and the extension of equipment life through variable frequency drives. The website can be found at http://vfds.com/vfdbenefits.html

Article 2: How to Specify Variable Frequency Drives - This article describes the process one should follow to identify what type of variable frequency drive needed for a specific application. The article also offers some alternative views on how to size drives. The article is found at http://vfds.com/vfdspecify.html

Article 3: Harmonic Mitigation Specification for Variable Frequency Drives - This article explains the importance of harmonic mitigation control and the potential damage it can do to one's electrical system. The article can be found at http://vfds.com/harmonic-mitigation.html

Can anyone offer an explanation to why I am have issues with this?

Webmaster emc123 (talk) 18:45, 14 February 2008 (UTC)