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Humphrey B. Bear
electronics forum beginner
Joined: 29 Jun 2006
Posts: 10
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 Posted: Sat Jul 15, 2006 9:53 pm Post subject:
DC Motor Driver Regenerative Braking
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I recently made a PWM-driven H-Bridge speed/direction controller for a 12V
180W DC brush motor (using the HIP4080A) and have now been asked to
re-design it incorporating regenerative braking. I'm having trouble getting
my head around a method of doing this. Can anyone suggest any links to
circuits or articles that might help?
.... Humphrey |
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John Popelish
electronics forum Guru
Joined: 29 Apr 2005
Posts: 1601
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| Posted: Sat Jul 15, 2006 10:34 pm Post subject:
Re: DC Motor Driver Regenerative Braking
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Humphrey B. Bear wrote:
| Quote: | I recently made a PWM-driven H-Bridge speed/direction controller for a 12V
180W DC brush motor (using the HIP4080A) and have now been asked to
re-design it incorporating regenerative braking. I'm having trouble getting
my head around a method of doing this. Can anyone suggest any links to
circuits or articles that might help?
|
The concept is that you use one of the appropriate switches and one
clamp diode to short the motor, briefly, using its self generated EMF
to drive the current up (ramp rate set by the EMF and motor
inductance) to the magnitude that produces the desired braking torque,
then open the switch and let the motor inductance pump that current
into the supply through the clamp diodes, like a flyback power supply
would. This works most reliably if you can monitor the current during
the process. Letting the current wind all the way to zero reduces the
switching losses for the next shorting part of the cycle, but lowers
the average braking torque relative to the peak current, so the peaks
have to be higher to get the same average breaking.
Repeat as necessary. |
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Humphrey B. Bear
electronics forum beginner
Joined: 29 Jun 2006
Posts: 10
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| Posted: Sat Jul 15, 2006 11:19 pm Post subject:
Re: DC Motor Driver Regenerative Braking
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"John Popelish" <jpopelish@rica.net> wrote in message
news:VJGdnRxMcJMJ8STZnZ2dnUVZ_r2dnZ2d@adelphia.com...
| Quote: | Humphrey B. Bear wrote:
I recently made a PWM-driven H-Bridge speed/direction controller for a
12V
180W DC brush motor (using the HIP4080A) and have now been asked to
re-design it incorporating regenerative braking. I'm having trouble
getting
my head around a method of doing this. Can anyone suggest any links to
circuits or articles that might help?
The concept is that you use one of the appropriate switches and one
clamp diode to short the motor, briefly, using its self generated EMF
to drive the current up (ramp rate set by the EMF and motor
inductance) to the magnitude that produces the desired braking torque,
then open the switch and let the motor inductance pump that current
into the supply through the clamp diodes, like a flyback power supply
would. This works most reliably if you can monitor the current during
the process. Letting the current wind all the way to zero reduces the
switching losses for the next shorting part of the cycle, but lowers
the average braking torque relative to the peak current, so the peaks
have to be higher to get the same average breaking.
Repeat as necessary.
|
Thanks, John. It's beginning to make sense now. I couldn't see how the back
EMF, which is usually lower than the supply voltage, could push current back
into the battery. So, in effect, for example, if the BL MOSFET is on and I'm
PWMing the AH MOSFET to control speed, then I need to turn on the AL MOSFET
for part of the time that the AH MOSFET is turned off. Is that right?
When you mention monitoring the current during the process, do you mean the
current through the motor while the AL MOSFET is turned on, (in the example
above)?
It is important that braking occurs automatically when the PWM duty-cycle is
decreased. I assume that the above process should be carried out the whole
time the motor is running, with the low MOSFET turning on for a short period
whenever the high-side MOSFET is turned off. Is this correct?
.... Humphrey |
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Genome
electronics forum Guru
Joined: 30 Apr 2005
Posts: 789
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| Posted: Sat Jul 15, 2006 11:46 pm Post subject:
Re: DC Motor Driver Regenerative Braking
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"Humphrey B. Bear" <not@me.com.au> wrote in message
news:44b963b9$0$21746$afc38c87@news.optusnet.com.au...
| Quote: | I recently made a PWM-driven H-Bridge speed/direction controller for a 12V
180W DC brush motor (using the HIP4080A) and have now been asked to
re-design it incorporating regenerative braking. I'm having trouble
getting
my head around a method of doing this. Can anyone suggest any links to
circuits or articles that might help?
... Humphrey
|
Before you get happy about the concept think about where the energy is going
and how you might switch the switches and what might give you the best
efficiency..... and why.
AB
CD
You might have A+D on for getting to full forward and then you might have
B+C for going full reverse. In between you might have a bit of C+D or A+D
to freewheel things a bit and avoid parasitic diode conduction and it will
all have an effect on the loop you stick around things to do it.....
But, you're biggest bugger is you will shunt the energy from the motor, and
its load, back into the supply. You might spend a lot of time being dead
clev about how you switch things on and off but if the supply can't cope
with the motor/load dump then you'll be bolloxed.
DNA
And then think about where the energy is going again |
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John Larkin
electronics forum Guru
Joined: 29 Apr 2005
Posts: 4320
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| Posted: Sun Jul 16, 2006 12:04 am Post subject:
Re: DC Motor Driver Regenerative Braking
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On Sat, 15 Jul 2006 23:46:37 GMT, "Genome" <mrspamizgood@yahoo.co.uk>
wrote:
| Quote: |
"Humphrey B. Bear" <not@me.com.au> wrote in message
news:44b963b9$0$21746$afc38c87@news.optusnet.com.au...
I recently made a PWM-driven H-Bridge speed/direction controller for a 12V
180W DC brush motor (using the HIP4080A) and have now been asked to
re-design it incorporating regenerative braking. I'm having trouble
getting
my head around a method of doing this. Can anyone suggest any links to
circuits or articles that might help?
... Humphrey
Before you get happy about the concept think about where the energy is going
and how you might switch the switches and what might give you the best
efficiency..... and why.
AB
CD
You might have A+D on for getting to full forward and then you might have
B+C for going full reverse. In between you might have a bit of C+D or A+D
to freewheel things a bit and avoid parasitic diode conduction and it will
all have an effect on the loop you stick around things to do it.....
But, you're biggest bugger is you will shunt the energy from the motor, and
its load, back into the supply. You might spend a lot of time being dead
clev about how you switch things on and off but if the supply can't cope
with the motor/load dump then you'll be bolloxed.
DNA
And then think about where the energy is going again
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Hey, if you look at it from a conservation of energy standpoint...
Crank up the h-bridge duty cycle to some goodly amount and let the
motor rev up to speed, and acquire a bunch of angular momentum sort of
stored energy. Now reduce the bridge-drive duty cycle. The h-bridge
average output voltage drops, so the motor back emf must be dumping
energy *into* the h-bridge, and the motor is being braked. Since (as
we all know) an h-bridge is 100% efficient, the energy being extracted
from the motor has to go somewhere, so it goes into the power supply,
where it came from in the first place.
So dynamic braking is sort of automagically free... just scrunch down
the drive duty cycle. Of course, the switches in the bridge must be
able to conduct in all directions, so they should be fets.
Did I get that right?
John |
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Humphrey B. Bear
electronics forum beginner
Joined: 29 Jun 2006
Posts: 10
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| Posted: Sun Jul 16, 2006 12:13 am Post subject:
Re: DC Motor Driver Regenerative Braking
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"Genome" <mrspamizgood@yahoo.co.uk> wrote in message
news:x7fug.6037$s4.5144@newsfe3-win.ntli.net...
| Quote: |
"Humphrey B. Bear" <not@me.com.au> wrote in message
news:44b963b9$0$21746$afc38c87@news.optusnet.com.au...
I recently made a PWM-driven H-Bridge speed/direction controller for a
12V
180W DC brush motor (using the HIP4080A) and have now been asked to
re-design it incorporating regenerative braking. I'm having trouble
getting
my head around a method of doing this. Can anyone suggest any links to
circuits or articles that might help?
... Humphrey
Before you get happy about the concept think about where the energy is
going
and how you might switch the switches and what might give you the best
efficiency..... and why.
AB
CD
You might have A+D on for getting to full forward and then you might have
B+C for going full reverse. In between you might have a bit of C+D or A+D
to freewheel things a bit and avoid parasitic diode conduction and it will
all have an effect on the loop you stick around things to do it.....
But, you're biggest bugger is you will shunt the energy from the motor,
and
its load, back into the supply. You might spend a lot of time being dead
clev about how you switch things on and off but if the supply can't cope
with the motor/load dump then you'll be bolloxed.
DNA
And then think about where the energy is going again
The supply is a 12V, 24Ah lead-acid battery, so the energy will just replace |
some of its charge.
I'll probably use a PIC16F876 to run the show. Previously, I used a HIP4080A
as the bridge-driver. It doesn't allow separate switching of the low-side
MOSFETs, so I'll probably use the HIP4081A this time. Still need to
double-check the datasheet to see if I can accomplish what I want.
I'd like to avoid the extra complexity of current monitoring, so timing is
the next major issue.
.... Humphrey |
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Genome
electronics forum Guru
Joined: 30 Apr 2005
Posts: 789
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| Posted: Sun Jul 16, 2006 12:25 am Post subject:
Re: DC Motor Driver Regenerative Braking
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"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:o00jb2tuvoqci66d9i4q7l950u0eqmhji1@4ax.com...
| Quote: |
Hey, if you look at it from a conservation of energy standpoint...
so it goes into the power supply,
where it came from in the first place.
Did I get that right?
John
|
Assuming your power supply can sink as well as source energy, or store the
excess somewhere, then yes.
Thank you for the clarification.
DNA |
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John Popelish
electronics forum Guru
Joined: 29 Apr 2005
Posts: 1601
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| Posted: Sun Jul 16, 2006 2:13 am Post subject:
Re: DC Motor Driver Regenerative Braking
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Humphrey B. Bear wrote:
| Quote: | Thanks, John. It's beginning to make sense now. I couldn't see how the back
EMF, which is usually lower than the supply voltage, could push current back
into the battery. So, in effect, for example, if the BL MOSFET is on and I'm
PWMing the AH MOSFET to control speed, then I need to turn on the AL MOSFET
for part of the time that the AH MOSFET is turned off. Is that right?
|
I think so. Note that this produces only dynamic braking, not reverse
torque at a standstill. You can also drive the motor current up in
the braking direction by applying the supply voltage in series with
the generated EMF, to be able to push up the braking current, even
down to zero speed. This is essentially 4 quadrant operation, where
the torque is independent of the rotation direction. This is quite a
bit more versatile then just dynamic braking, where you rely on motor
speed (generated EMF) only, to drive the braking current.
| Quote: | When you mention monitoring the current during the process, do you mean the
current through the motor while the AL MOSFET is turned on, (in the example
above)?
|
Having a current monitor that tells the control circuit the magnitude
and direction of the motor current, regardless of which switches and
or diodes are conducting, is very handy, when you need to control
torque as well as speed, since torque is proportional to current (for
a fixed field excitation, or permanent magnet field), to a first
approximation.
| Quote: | It is important that braking occurs automatically when the PWM duty-cycle is
decreased. I assume that the above process should be carried out the whole
time the motor is running, with the low MOSFET turning on for a short period
whenever the high-side MOSFET is turned off. Is this correct?
|
I think you would need a current feedback scheme to control the pulse
widths to make the braking smooth and variable, as desired. |
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Rich Grise
electronics forum Guru
Joined: 24 Mar 2005
Posts: 3971
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| Posted: Fri Jul 21, 2006 12:22 am Post subject:
Re: DC Motor Driver Regenerative Braking
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On Sat, 15 Jul 2006 22:15:47 -0400, John Popelish wrote:
| Quote: | Humphrey B. Bear wrote:
....
It is important that braking occurs automatically when the PWM
duty-cycle is decreased. I assume that the above process should be
carried out the whole time the motor is running, with the low MOSFET
turning on for a short period whenever the high-side MOSFET is turned
off. Is this correct?
I think you would need a current feedback scheme to control the pulse
widths to make the braking smooth and variable, as desired.
|
As long as we're talking about fantasy regenerative braking systems, how
about feel feedback? i.e., the harder you press the pedal, the harder
you're braking, and the harder the pedal pushes back. With ordinary
hydraulic brakes, you can feel with your foot how hard you're pressing
the pad against the rotor, or is the deceleration enough feel feedback?
I'd hate to have a pedal with no feel feedback if I were in traffic and
saw brake lights up ahead - you have to brake hard enough not to rear-
end the guy in front of you, but not so hard that you get rear-ended by
the guy behind you.
Thanks!
Rich |
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Mark Fortune
electronics forum addict
Joined: 06 Jul 2006
Posts: 57
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| Posted: Fri Jul 21, 2006 2:46 am Post subject:
Re: DC Motor Driver Regenerative Braking
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Rich Grise wrote:
| Quote: | On Sat, 15 Jul 2006 22:15:47 -0400, John Popelish wrote:
Humphrey B. Bear wrote:
...
It is important that braking occurs automatically when the PWM
duty-cycle is decreased. I assume that the above process should be
carried out the whole time the motor is running, with the low MOSFET
turning on for a short period whenever the high-side MOSFET is turned
off. Is this correct?
I think you would need a current feedback scheme to control the pulse
widths to make the braking smooth and variable, as desired.
As long as we're talking about fantasy regenerative braking systems, how
about feel feedback? i.e., the harder you press the pedal, the harder
you're braking, and the harder the pedal pushes back. With ordinary
hydraulic brakes, you can feel with your foot how hard you're pressing
the pad against the rotor, or is the deceleration enough feel feedback?
I'd hate to have a pedal with no feel feedback if I were in traffic and
saw brake lights up ahead - you have to brake hard enough not to rear-
end the guy in front of you, but not so hard that you get rear-ended by
the guy behind you.
Thanks!
Rich
|
Since (from my understanding) regenerative braking does not wear out
like abrasive pads, would a block of rubber[1] under the brake pedal not
have the same effect? Just thinking about all that energy wasted in
pushing the pedal back.
[1] obviously the rubber should be firm so as to provide a sense of
feedback, but not so firm that it stops you braking effectively.
Mark |
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Clifford Heath
electronics forum Guru Wannabe
Joined: 01 May 2005
Posts: 140
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| Posted: Fri Jul 21, 2006 2:51 am Post subject:
Re: DC Motor Driver Regenerative Braking
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Rich Grise wrote:
| Quote: | As long as we're talking about fantasy regenerative braking systems, how
about feel feedback? i.e., the harder you press the pedal, the harder
you're braking, and the harder the pedal pushes back. With ordinary
hydraulic brakes, you can feel with your foot how hard you're pressing
the pad against the rotor, or is the deceleration enough feel feedback?
|
It is noteworthy that F1 brake "pedals" are just immobile (or nearly)
force sensors. The deceleration is already *too much* feedback  |
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