Regenerative braking dc motor controller

[calhau0]

Hi

i'm trying to implement regenerative braking on a simple dc motor controller
i'm aplying a pwm signal to the mosfet to control the motor speed, but i can't figure out how to put the regen part working
**broken link removed**

i was hoping that when the M1 mosfet is off, that the motor current would flow trought D1 diode but tha doesn't happen

can anyone help me with this?

thanks !

 

[alec_t]

Is V1 really 0V? That won't help

i was hoping that when the M1 mosfet is off, that the motor current would flow trought D1 diode but tha doesn't happen

Are we talking about what happens in a simulation or in real life?

 

[ikalogic]

with that circuit you can only make the motor turn in 1 direction.

you need a push pull driver (a driver than can source and sink current). Only then you will be able to do braking.

ideally, you need an H bridge. what about the l293D as an easy start?

 

[Ubergeek63]

v1= motor max
diode across motor
regen fet across motor

 

[ronv]

Regen

You need a FET across the motor like attached.

 

[calhau0]

Is V1 really 0V? That won't help
Are we talking about what happens in a simulation or in real life?

V1 is 200v
we are talking in real life

with that circuit you can only make the motor turn in 1 direction.

you need a push pull driver (a driver than can source and sink current). Only then you will be able to do braking.

ideally, you need an H bridge. what about the l293D as an easy start?

i'm only interested going forward i'm not interested in backwards movement

You need a FET across the motor like attached.

how does that work ? why do i need M2? is M2 on when M1 is off?

 

[tcmtech]

Are you trying for actual regenerative braking where the motor puts power back into the the battery or dynamic braking where the motor works against a partial short and slows things down by drag only?

To do regenerative braking the motor has to put out more voltage than the battery was supplying which means you either need some sort of boost circuit to send the braking power back to the battery or the motor has to be spun faster than it was going when powered by the battery.

 

[calhau0]

i'm trying to do regenerative braking not dynamic braking, do i need to make a buck boost circuit in order to regen energy? to the battery isn't there a simplier solution?

 

[tcmtech]

The only way to send power back to the battery is to raise the input voltage higher than the battery's open circuit voltage.

Boost converters, speeding up the motor, or dropping the battery voltage by combinations of series and parallel switching are the three that come to my mind.

 

[ronv]

how does that work ? why do i need M2? is M2 on when M1 is off?

Yes M2 is on when M1 is off. It will charge the battery when the motor back emf is higher than the PWM voltage. On the surface it looks like the diode shoud work, but it will not.

 

[calhau0]

to charge a Li-ion 200v battery how higher must the generated voltage be? 210v? 250v?

View attachment 63593

will this new sche. work? only added boost converter to the generated motor voltage

 

[Mr RB]

...
Yes M2 is on when M1 is off. It will charge the battery when the motor back emf is higher than the PWM voltage. On the surface it looks like the diode shoud work, but it will not.

Actually a half bridge will charge the battery from practically any motor speed, motor voltage does not have to be higher than battery voltage.

 

[jpanhalt]

Is the DC motor series wound, shunt wound, or PM?

John

 

[calhau0]

Actually a half bridge will charge the battery from practically any motor speed, motor voltage does not have to be higher than battery voltage.

how does an half bridge charge the battery?

Is the DC motor series wound, shunt wound, or PM?

John

it's a PM motor

 

[Mr RB]

how does an half bridge charge the battery?
...
it's a PM motor

Because a DC permanent magnet motor behaves like a current drain (load) in series with an inductor when it is accelerating but behaves as a current source (PSU) in series with an inductor when it is decelerating.

As a current source (PSU) in series with an inductor, the half bridge acts like a boost converter with the bottom FET shorting the motor (current builds up) then the top FET closes and current is returned to the battery even though the battery voltage is higher than the motor generated voltage.

 

[calhau0]

**broken link removed**
but how can a current flow if M1 is closed?

so when i want the motor to go forward i have the M2 open and the M1 is opening and closing due to pwm , but when i want to brake the M1 will be closed and the M2 will be pwm (which duty cycle should i choose?) but if M1 is closed there is no way for the current to flow, if at least there was a diode in parallel to M1

 

[Mr RB]

You have to stop thinking of it like a motor "on or off" situation.

The halfbridge switches at a duty cycle, that makes an average DC voltage out. If the motor is turning slower than that DC voltage it operates as a motor and draws current fromt he battery. If the motor is operating faster than that DC voltage it operates as a generator and returns current to the battery.

It's exactly comparable to a bi-directional buck SMPS converter that will send current either way, depending on the levels of the two voltages compared to PWM duty.

 

[calhau0]

thanks!! i think a got it now

but the diode D3 isn't necessary is it?

thanks again!

 

[Ubergeek63]

thanks!! i think a got it now

but the diode D3 isn't necessary is it?

thanks again!

depends on if you have a high speed substrate diode in your FET

 

[ronv]

The diode is there for the brief time before the top fet turns on.