Modeling a motor winding

[Mike Young]

I want to model a motor winding in MicroCap 8. Or SPICE 3, whichever. Would
it be too simplistic to model it as a simple inductor? I'm interested in
analyzing the chopped PWM transients on the driver and power MOSFET.

 

[Terry Pinnell]

I want to model a motor winding in MicroCap 8. Or SPICE 3, whichever. Would
it be too simplistic to model it as a simple inductor? I'm interested in
analyzing the chopped PWM transients on the driver and power MOSFET.

See the section of a fairly long thread, starting here, where I had a
lot of expert advice form Tony Williams:

Newsgroups: sci.electronics.design
Subject: Re: Simple 555 PWM - disappointing performance
Date: Thu, 26 May 2005 09:43:18 +0100

 

[Mike Young]

See the section of a fairly long thread, starting here, where I had a
lot of expert advice form Tony Williams:

Newsgroups: sci.electronics.design
Subject: Re: Simple 555 PWM - disappointing performance
Date: Thu, 26 May 2005 09:43:18 +0100

Thanks. I snagged the model, but only had time to browse the subsequent
discussion a bit; will read it more carefully later. I also didn't read the
fine print when I dl'ed LTSpice. Is it a demo with limitations? or is it the
real deal?

Anyway, it's a stepper, with much simpler physics than a PMDC. I'm more
interested in what's happening on the gate side of the MOSFET. Wondering if
I can't make it work with an opamp comparator for current sense/limiting
instead of the more traditional PWM chopping. Quad opamps are pennies these
days. I think I can squeeze a whole second motor onto the PIC if it can
off-load the current limiting part. (More for futzing around's sake than any
real economy. How many controllers would I need to make to recoup the $1.50
I save on the second PIC? What an upside down world. The protection diodes
alone cost more than the power MOSFETS.)

 

[R Adsett]

Thanks. I snagged the model, but only had time to browse the subsequent
discussion a bit; will read it more carefully later. I also didn't read the
fine print when I dl'ed LTSpice. Is it a demo with limitations? or is it the
real deal?

Anyway, it's a stepper, with much simpler physics than a PMDC. I'm more
interested in what's happening on the gate side of the MOSFET. Wondering if
I can't make it work with an opamp comparator for current sense/limiting
instead of the more traditional PWM chopping. Quad opamps are pennies these
days. I think I can squeeze a whole second motor onto the PIC if it can
off-load the current limiting part. (More for futzing around's sake than any
real economy. How many controllers would I need to make to recoup the $1.50
I save on the second PIC? What an upside down world. The protection diodes
alone cost more than the power MOSFETS.)

I've seen it done. It was used as a current control loop on a motor
controller

Robert

 

[Riscy]

You can apply PIC using pulse skipping technique, you have fixed pulse
width and use ADC to monitor output voltage, if the voltage goes above
threshold, you skip pulse. It very simple and effective but poor
ripples performance. The advantage of fixed pulse width that the
current ramp is the same (under discontinous mode).

The LT model is the real thing.

The key thing is the current ramp that feed into transformer (or
inductor). Make sure the core does not get into saturation by excessive
current ramp, where magnetic flux density exceed the core specification
(Bsat). There is simple equation to use in Philip Ferrite Core
datasheet, this is good starting point for transformer/inductor
development.