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PMDC motor back EMF control circuit designing guidline

Posted by: d8118135198 on Wed, 10/09/2019

Dear All,
We are using PMDC motor in one of application and supply voltage is applly through rectifier bridge circuit to convert AC to DC.
When motor is operated on no-load condition, we noticed some additional voltage due to back EMF at the rectifier terminal which is almost 35% higher than the rated voltage.

If we are using 220vdc PMDC motor,
input at rectifier circuit = 220Vac
output at rectifier circuit = 210Vdc

But when the motor runs,
the output of the rectifier circuit = 300Vdc.

In such a case, the motor is rotating with inappropriate speed against rated speed.
This is obviously due to back EMF which needs to control by placing the additional circuit in parallel to the rectifier bridge circuit.

Suggest me an appropriate circuit to protect bridge rectifier or ommit back emf from motor.


Submitted by PI-Artoo-Detoo on Fri, 10/11/2019

If your intent is to protect the bridge rectifier from the induced back emf you could use a diode in series after the bulk capacitor and use a smaller decoupling capacitor close to the inverter stage.
Do you have a speed regulation implemented in your PMDC motor control?