Re: switchmode gyrator

john larkin <JL@gct.com> wrote:

On Fri, 15 Nov 2024 21:28:58 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
 

On 13/11/2024 9:05 am, john larkin wrote:

On Tue, 12 Nov 2024 19:44:39 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
 

On 11/12/24 16:49, john larkin wrote:

On Tue, 12 Nov 2024 07:49:13 -0500, legg <legg@nospam.magma.ca> wrote:
 

On Sat, 09 Nov 2024 06:08:40 -0800, john larkin <JL@gct.com> wrote:
 

 
 
Inductors are awful. Their energy storage is worse than electrolytic
caps by about a factor of 1000.
 
https://electronics.stackexchange.com/questions/326177/energy-density-comparison-between-inductors-and-capacitors
 
One could in theory make a switchmode gyrator that would make a
capacitor look like a programmable-value inductor.
 
I have an application for that, but it would take too much engineering
and runtime complexity to make it worth doing. I guess I'll just have
to buy a bunch of giant, heavy custom toroids.

 
I'm sure that there are other reasons why an inductor
will be used besides the lack of time/energy/resources
to 'design them out'.
 
Energy storage is just one means to an end.
 
RL

 
Sure. We want to design some dummy loads that will simulate relays,
solenoids, stepper motors, torque motors, with programmable R and L.
Seemed to me that using caps to make fake inductors would be a good
way to do that.
 
It's at least an interesting idea to play with. Maybe we can
switchmode simulate R+L all at once. We would have to store energy and
dissipate power to do that.

 
Relays and motors do not behave like simple inductors. For example,
while a relay armature is moving, the back EMF is high enough to
make the current _drop_ briefly. Modelling that requires more than
a simple gyrator.
 
Jeroen Belleman

 
My customer is building giant rackmount boxes full of heavy inductors
as part of his dummy loads. We want to replace them.
 
Given a generalized switching impedance simulator, I guess one could
model a DC motor.
 
I am considering a powered impedance simulator, not the theoretical
gyrator. Just sort of a gyrator.
 

 
Many inductive loads can produce kilovolts when switched off suddenly.
If you build a switched-mode equivalent, unless it contains a large real
output inductor, your class-D output stage might need supply rails of
kilovolts to emulate the real inductor accurately. That sounds expensive.

 
An electronic load would of course have specified voltage, current,
and power limits.
 
But some of the simulated inductance - a few mH maybe - could be real
inductors, and they would fly back a bunch. We do need to accept a
customer PWM drive and sort of behave right.
 
I don't think that kilovolt flybacks are common in real areospace
systems. That could damage wire insulation and interfere with other
stuff.
 

 
If the load you are emulating contains a TVS or other clamp as part of
the load, then it would be easier to emulate, but you wouldn't be able
to emulate the fault condition where the clamp fails open.
 

 
Yes, the customer's drivers have flyback diodes or equivlent, or just
a continuous low-Z PWM drive. We can't simulate every corner case,
lightning strikes or major system faults.
 
It's just an interesting problem, simulating a pretty high power
inductor without a hundred pounds of iron. What I'd never thought much
about is how terrible inductors are at storing energy.
Inductor:capacitor:supercap:battery are roughly 1000:1 steps in energy
density.
 
 
 
 

On the plus side, you can (so to speak) charge and discharge them a good
1e9 times faster than your average battery.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics