Using both regenerative and mechnical braking systems?

Discussion in 'General Electronics Chat' started by jegues, Aug 21, 2013.

  1. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    Evening gents,

    I am just trying to understand how motor controllers accommodate both a regenerative and mechanical braking system.

    Is there a simple control method they employ to have both mechanical and regenerative braking systems working together in harmony?

    The control of regenerative braking by itself seems simple enough, but once you throw mechanical braking into the mix things seem get more complicated.

    How is the regenerative braking of the motor supposed to adjust itself for any the changes made in the mechanical brake by the operator? Surely you can't just go by the physical position of the brake handle, as the operator uses feedback from both the position and resistance felt on the brake handle to better adjust his braking.

    Any ideas?

    Thanks again!
     
  2. #12

    Expert

    Nov 30, 2010
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    Just guessing, but, the regenerative part is passive. You can switch it on with a brake pedal switch, and even modulate its admittance with the movement of the brake pedal. Then, it accepts energy that is proportional to the speed of rotation. Press harder on the pedal and the hydraulic system starts shoving the brake pads into the rotor (or brake drum).
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Regenerative braking as its name implies uses the BEMF of the motor fed into a Braking resistor, the degree of braking is reduced as the rpm diminishes, less BEMF.
    There is little in the way of coordination between Regen and mech AFAIK?
    What system are asking after?
    Max.
     
  4. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    Hi MaxHeadRoom! :)

    In our case we want to use the regenerative braking to charge a bank of batteries, so current supplied from the EMF of the motor won't be bled across a braking resistor, but rather to sent back into the battery bank.

    I'm not sure what you're asking (or telling) me here.

    Are you trying to say that the both the regenerative and mechnical braking are easily coordinated?


    I don't know what this question is suppposed to mean either.

    I am asking about mechnical and regenerative braking in the context of motor controllers.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    OK. So where does the mechanical braking come in?
    See previous comment

    You asked a vague question, I realize it might be the dynamic braking of motors, but what equipment and the reason for the question?.

    There is no real context in your OP?

    The more information included with a question helps a great deal and avoids mind reading!
    Is this a stationary equipment, electric car, Locomotive??

    Max.
     
    Last edited: Aug 21, 2013
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I think you're thinking that regen braking is more complicated than it actually is. Usually it's a fixed torque, which is enough to slow the load down faster than a coasting deceleration, but it isn't usually strong enough to bring it to a screeching halt like a mechanical brake.

    If this is for a vehicle application or other application where you want to control a variable degree of regenerative braking as well as a variable degree of mechanical braking concurrently, then it will be dependent on the dynamics of the vehicle. Charge rate of batteries, size and amp rating of motor, weight of vehicle, etc. It will probably have to be worked out empirically. If I were building an EV and trying to work out the regen braking, I would probably reserve the first x% of brake pedal travel for regen braking, and limit the variable regen to the charge rate of the batteries. Once the charge rate has been reached, the mechanical brakes start to engage. The x% would correspond to the changeover point between regen and mechanical braking, and would be set to a point where the changeover cannot be felt by the driver. I don't know if this the best solution,just what what I would try first. There should be no problem with continuing to regenerate while mechanically braking. The regen should continue assisting the mechanical brakes at a fixed torque which corresponds to the charge rate.
     
  7. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    Hi strantor! :)

    This very solution had been suggested to me on another forum, and I am considering pursuing it.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    To sum up, the one main problem is that regen. braking used for recharge of batteries is too much of a variable, unless a semi-sophisticated system is designed to increase/decrease mechanical braking with somehow monitoring the amount of regen current is carried out.
    If this is what is intended then more information on the equipment would be needed?
    Max.
     
  9. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    Hi MaxHeadRoom! :)

    I wasn't planning on providing any specific context with regards to my question.

    It was intentionally left to be as "open" as possible, since I'm simply trying to gain a better understanding of the coordination between regenerative braking and mechanical braking in motor control.

    I'm not designing for any particular application. (Not yet at least!)

    What are some of the common methods used to coordinate both mechanical and regenerative braking? What do they use for stationary equipment? Electric cars? Locomotives?

    If you need a particular context to work from, assume it is for an electric vehicle. (Although it doesn't have to be!)
     
  10. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    Hi MaxHeadRoom! :)

    In post #6, strantor described a particular scheme that could be used to coordinate both the mechnical and regenerative braking.

    Is something like this what you're refering to as a "semi-sophisticated system is designed to increase/decrease mechanical braking with somehow monitoring the amount of regen current is carried out."?
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    What you need to look at is called 2 quadrant(no reverse) or 4 quadrant(forward and reverse) motor control. This is a link that explains some of the basics of it -
    http://www.4qd.co.uk/fea/regen.html There is a lot of good stuff on that link about motor controllers.

    And Google will give much more about 2 and 4 quadrant control.
     
  12. Smoke_Maker

    Active Member

    Sep 24, 2007
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    It's all in the programming of the motor controller, you want the brake pedal position switch to apply regen in proportion to pedal travel and pressure. The motor controller will apply the correct amount of regen to make it feel like your using hyd. brakes to stop.

    The devil is in the details, the motor controller needs to know battery state of charge so it doesn't overcharge the batteries. The motor controller needs to talk to the battery management system and decide how much regen can be applied and how much hyd. brakes needs to be applied to match brake pedal travel and pressure.

    I have removed and replaced a brake pedal assembly on a Ford Escape because of a traction control problem, it was a big thing with heavy springs, switch's, potentiometer, and a high pressure charged cylinder.

    When the traction control light came on, it disable the regen and the brake pedal dropped about half way to the floor board and it was all hyd. brakes stopping the vehicle, and then your heart settles back down to where it belongs.
     
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