Regenerative Power on DC bus between DC motor and voltage supplier

Question

Currently, I am looking for a back-EMF solution for brushless DC motor drive. My input voltage for motor driver is 48V (which starts at 50V level and starts to decline until 35V as a feature of fuel cell). However, as I try to accelerate DC motor back and forth during motion, I observe a regenerative power on the input of the motor driver. (after 56V the motor driver disables itself)

Do you know if there is any strategy to compensate this back-EMF on DC bus? Is there any suitable product which I can use for this purpose?

Here is what I saw on the screen of oscilloscope (I just supplied the motor driver with 28V)

Supplied with 48V. The driver shut downed itself

Answer 1

If you can put enough capacitance on the DC bus to absorb the energy without going overvoltage that would be the simplest solution without wasting energy.

If not, a common approach is to use a bank of resistors and a comparator on the DC bus. When the voltage approaches the maximum allowable the comparator will turn on, which turns on a MOSFET and puts the resistor bank across the DC bus to dissipate the energy as heat. The comparator should have some hysteresis to avoid high frequency chatter.

Lastly there are more complicated regenerative schemes to store the recovered energy in a battery or regenerate it onto the AC line.

Answer 2

This is only partially related to the BackEMF of an electrical machine.

Assuming you have a 4-quadrant controller & you are ACTIVELY decelerating the rotor, what is occurring is the transfer of energy from the rotor ( \$\frac{1}{2}J\omega^2\$ ) and the stator inductance ( \$\frac{1}{2}LI^2\$ ) onto the DCLink capacitance (\$\frac{1}{2}CV^2\$)

The voltage on the capacitance must rise as the energy is transferred.

Three ways to minimise or deal with the increased voltage

1. Increase the DClink capacitance close to the H-Bridge.

With an increase in capacitance the final voltage for the same energy transfer will have been reduced

2. Decrease controller bandwidth

It is not stated whether you have a form of PI closed loop control, nor whether you have a speed loop, but reducing its bandwidth and the rate it can decelerate will reduce the rate of energy tranfer which will reduce the end voltage

3. Incorporate a resistive brake circuit

By placing a Resistor + FET across the DClink (plus a freewheel diode across the resistor) & a DClink hysteretic monitor (comparator), the FET will "chop" the DClink between predefined thresholds (say .. 54V -53V). As long as the resistor value and power rating have been appropriately selected, the DClink will be maintained below the level of concern

Answer 3

I believe what you are looking for is a flyback diode on your DC motor. Could you put one of these inline with your DC supply to the motor? That way when the current reverses on the line you would block it and allow the motor to play out the stored energy. These are used a lot in automotive industry to deal with coil collapse induced back EMF. Look for Flyback Schottky Diodes and see if this is what you are looking for.