Hello Everyone,

I have a few fundamental doubts on the effects of back emf on a dc motor and was hoping to have them cleared.

Firstly , Let me explain the hardware setup. I have a DC-link capacitor voltage of about 300 V which connects to 3 parallel half bridges and the midpoint of each bridge connects to the motor.

What would be the effect of the back EMF at rated speed of motor on the DC Link voltage?, If the dc link voltage is not regulated, would the net resultant voltage across the dc bus be (dc bus voltage - Vback emf)?

Secondly:

I would like to include some kind of back emf protection in case the motor stops suddenly, the voltage across the DC link capacitor raises sharply,

My first thought is to use a brake chopper to waste the excess energy across it. But in order to do this, (calculate the maximum power that would be needed to be dissipated(hence choosing the appropriate brake resistor values)) , how do i calculate what will be the maximum voltage the dc-bus will raise to incase of a sudden motor stoppage? Can i assume the worst case to be 2x Dclink voltage?

Thanks!

I have a few fundamental doubts on the effects of back emf on a dc motor and was hoping to have them cleared.

Firstly , Let me explain the hardware setup. I have a DC-link capacitor voltage of about 300 V which connects to 3 parallel half bridges and the midpoint of each bridge connects to the motor.

What would be the effect of the back EMF at rated speed of motor on the DC Link voltage?, If the dc link voltage is not regulated, would the net resultant voltage across the dc bus be (dc bus voltage - Vback emf)?

Secondly:

I would like to include some kind of back emf protection in case the motor stops suddenly, the voltage across the DC link capacitor raises sharply,

My first thought is to use a brake chopper to waste the excess energy across it. But in order to do this, (calculate the maximum power that would be needed to be dissipated(hence choosing the appropriate brake resistor values)) , how do i calculate what will be the maximum voltage the dc-bus will raise to incase of a sudden motor stoppage? Can i assume the worst case to be 2x Dclink voltage?

Thanks!

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