Electronic – Sensing BLDC motor torque using a current sensor

brushless-dc-motorcurrentcurrent measurementmotortorque

As it is commonly known, the torque supplied by a motor is directly proportional to the current it draws. So when a motor is under heavy load, the torque required will be more hence it would draw more current

For a BLDC motor, the current is supplied via three phases which are switch by a motor driver. But this motor driver is supplied with a single DC supply.

Can I reliably measure the torque provided by my motor by measuring the current drawn by the driver?

My motor is currently mounted as part of a robotic arm and there is PID control loop for position control.

I only need to get an idea of the current load and detect load anomalies (like an impact i.e. higher load or loss of payload i.e. lower load etc).

Given that I can calculate the nominal load at any position and hence calculate the nominal current drawn, is it a good idea to use current sensing for this kind of load sensing?

Is there any research on this which analyses this method of torque control/load sensing which I can refer to?

Best Answer

It depends on the motor driver, but in the general case you can't expect the driver input current to equal the motor current. This is because good motor drivers are essentially switching power supplies, using the inductance of the motor as a integral part of the supply. The current thru a winding can be higher than the supply current, just like the output current of a buck switcher can be higher than the input current.