What is DC Injection Braking? - Problem Solved - YouTube

Welcome to the first edition of problem solved here at KEB America.

I'm here with Carlton stripe, an application engineer. I want you to tell

us what our topic is for the day. Today is DC injection braking. You're

gonna hear all about it in just a second. Let's do this.

I'm here with Carlton Stripe.

He's an application engineer and he's gonna tell us a little bit about DC

injection breaking. So Carlton, can you give us an overview of what it is.

Yeah, so DC braking is a method for

three-phase AC induction motors. It's a method to decelerate a load of high

inertia moving at high speed to decelerate it quickly and effectively

without friction components or letting the load coast to a stop. So out in the

field what would be some applications where you would implement this type of

braking? Yeah, so DC braking is best used for trying to decelerate a load

that has high inertia moving at high speeds as I mentioned. One example that

might come to mind is that of like a rotary grinding wheel. If an operator is

working on it grinding a piece of aluminum or metal and they want to stop,

not emergency stop, but just bring the motor and the load to a zero

speed position, you can use DC braking to decelerate that load, because that high

inertia, you know if the power was just removed

it could take a long period of time, may be multiple minutes to bring to a stop,

just based on coasting through friction. So would you be able to give me a

demonstration using the setup here of how DC injection braking works?

Of course, we can set it up and show you with and without DC braking. All right here

we have a little demo set up to demonstrate DC braking. We have an F5

drive that's programmed into an open loop configuration, and a small AC

three-phase induction motor here. In this drive I have programmed default parameters

for open loop control. And in open-loop drives from KEB we

have default parameters set up for DC braking capability. The only modification

I made for this example is I lowered the maximum voltage just slightly, just to

accommodate the smaller motor here for our example. So I'm gonna start up the

motor. And we can see the motor will start and spin at about 40 Hertz here.

And if I were to remove the AC power the motor would slowly coast to a stop.

Now, if we had a high inertial load like a big grinding wheel or something on here

that could take a considerable amount of time to coast to a stop through friction.

But now we will ramp the motor back up to speed, and we'll apply our DC braking

and we can watch how fast the DC braking stops the load. Almost immediately it

brings it to a nice halt. And then the DC braking by default parameters will run

for a programmed amount of time and then put the drive into LS. And then if the DC

braking input is removed, motor function will continue.

And so what would be some pros and cons to

using this in the field? So a definite pro is with DC braking you

don't need any additional components. There's no friction brake that's

required. Literally it's just using the drive and the motor itself, which you

already have. So there's no extra braking equipment that is needed. No wear

components that wear out. So essentially there's really no components that need

to be replaced or purchased in addition to the components you might already have

in your industrial automation application. You also, with high inertial

loads trying to decelerate them through the deceleration ramp of the drive,

pushes a lot of that regenerative energy back into the drive, and sometimes can

cause an over-voltage or an E.LP error. One limitation however of DC braking, is that

applying a direct current to the stator almost is as shorting, it almost acts as

a short-circuit to the coil, to the windings inside the motors. So you know

that's something that you want to be cautious of and not apply the DC braking

for very long. So DC braking should not be

used to hold a load, it should only be used to quickly decelerate a load and

then removed so as to not overheat the motor. I hope we learned something

Carlton here is a very smart guy and we're grateful to have him here at KEB

America. So that was our first episode of Problem Solved. We look forward to giving

you more insights into different automation applications.