On Sat, 22 Dec 2012, Steve Stallings wrote:
> Date: Sat, 22 Dec 2012 18:17:39 -0500
> From: Steve Stallings <steve...@newsguy.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "'Enhanced Machine Controller (EMC)'" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Pid saturated, was: Servo error
>
> OK, now I still need more education. Why is a bare H-bridge
> driven with PWM not equivalent to voltage mode? I thought
> the duty cycle of a PWM drive was effectively integrated
> by the inductance of the motor such that the percent duty
> cycle was equivalent to percentage of bus voltage on the
> H-bridge as far as the motor was concerned.
A PWM drive _is_ voltage mode
>
> Can you give an intuitive description or examples of a
> second order system as compared to a first order system?
A PID position loop that controls a torque mode drive is a second order
system. That is there are 2 cascaded integrators in the control loop (velocity
is the integral of torque over time and position is the integral of velocity
over time)
A PI loop that controls motor current by PWM voltage is a first order system.
that is there is only one integrator (the current is the integral of V/L over
time)
Note that real systems are never purely first or second order.
>
> Thanks,
> Steve Stallings
>
Peter Wallace
Mesa Electronics
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