Voltage Controlled Inductance for High Power Applications

Discussion in 'General Electronics Chat' started by Jason Moore, Feb 12, 2015.

  1. Jason Moore

    Thread Starter New Member

    Feb 12, 2015
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    I am trying to explore ideas of how to automatically adjust an inductor's impedance for matching reasons from 5mH to 12mH for an audio application. A big problem is my input voltage AC signal is large, typically 300-600Vp and has different configurations to operate between 12kHz to 18kHz. My load varies somewhat with different devices but is capacitive at about 13nF. Currently I manually change out the inductance values based upon what frequency I operate at and that is a big hassle for configuration management. I would like to be able to create a single variable voltage controlled inductance device where the voltage would be controlled by the frequency of operation. The ideas I have looked at so far are 1) transformer device changing the air gap with a mechanical actuator. Haven't found any real products like this. 2)Adding impedance to a fixed inductance by varying the transconductance of a CE class A amp through the varying the bias voltage. Limited by the DC supply voltage needed because of the large AC signal. 3) Having a tapped inductor with small inductor increments and switch to choose between them. Not very smooth. 4) Roller Inductor, big and bulky, power hungry, antiquated. Any better ideas?
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
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    Maybe an movable iron core might work if the current is low enough that you can get the number of turns high enough to start with.
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
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    look up "magnetic amplifier" a form of inductor that varies its inductance with a vafying magnetic field provided by a bias winding. a simple demo is to measure the secondary inductance of a transformer while varying a dc current through the primary.
     
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  4. Jason Moore

    Thread Starter New Member

    Feb 12, 2015
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    I have been doing research on the magnetic amplifier and similar devices like the transductor. Does the magnetic amplifier have to be partially saturated to have an affect on the inductance? What I think I understand is the clipping of the top half of the waveform from saturation in the core lowers the total change in flux, which lowers impedance and therefore raises current. This make the output really distorted. I am trying to see if there is a way to use this device to vary the inductance and still keep the output linear.
     
  5. uwed

    Member

    Mar 16, 2015
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    A H-bridge inverter with a proper current control can behave like an inductance with valiable inductance (and capacitance if required). Actually just like a small single-phase version of a STATCOM. Nice and smooth, but complexer than other solutions (I only simulated this up to now). Alternatively, I would go for a electronic tap-changer kind-of solution as you list as point (3).
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the magnetic amplifier is linear if p0roperly designed. only goes into clipping at the upper limits of current.
     
  7. Jason Moore

    Thread Starter New Member

    Feb 12, 2015
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    Have any suggestions for design references?
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    technology has gone beyond magnetic amps now, power lines use scr packs to switch inductors into or out of high voltage power lines to adjust power factor now. and most power supplies that used mag amps to regulate the output of the supply by varying the ac input to the supply use newer thyristors now. I dont have anything here except a couple of older lasers that use mag amps now, but there is a little info on them at http://www.sparkbangbuzz.com/ low power stuff tho.
     
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