moved- FPGA based control of BLDC Motor (BLDC , FPGA , ADC , IGBT , MOSFET , 3 Phase)

[FvM]

Specified starting currents would flow if you apply the nominal motor voltage to the stopped motor. You shouldn't do that.

 

[umargill]

Do you mean that I should not attempt to drive the motor (and neither I should apply a voltage) when it is stationary? What it means? Pretty strange, isnt it?

Of Course the motor will stop and start moving many times during the whole operation.

Please elaborate your comment.

Reagrds

 

[FvM]

My post's emphasis is on not "applying nominal voltage to the stopped motor". If the power stage can't handle the high inrush current, or you want a smooth motor start for other reasons, you'll supply a reduced voltage by using pwm.

The situation is quite similar to a brushed PMDC motor. If you simply switch on the supply voltage, the starting current is only limited by the armature DC resistance, producing a high inrush current. This may be O.K. for small motors, otherwise the motor voltage has to be ramped during startup.

 

[schmitt trigger]

Respected All!


Further, can anyone explain me the difference between motor stall current and motor starting current?

Regards

They are the exact same representations of what is called locked rotor amps (LRA).
When a rotor is not moving and therefore no back-EMF is developed, the only thing that limits the armature current is the winding's resistance. This is a characteristic of ALL motors.

Therefore, as FvM says, you have to soft-start the motor, either of two methods:
-slowly ramp the voltage up.
-or a better solution, measure the motor's current, and keep it within safe limits of your driver.

Bear in mind that in a BLDC motor, torque is to a first degree approximation directly proportional to current. Therefore if you limit the current, you also prevent mechanical damage in case of the rotor getting stuck (think, for instance, of a sheet of paper jamming in a printer).

 

[KlausST]

Hi,

the max voltage with a stalled motor:

max_stalled_voltage = max_rated_current * DC_resistance

Klaus

 

[umargill]

OK perfect. FvM, Schmitt Trigger and KlausSt

I now fully understand what you meant. Many thanks.

One Last Question:

Hall Effect Sensors give information about Rotor Speed only. How to detect position of the Rotor (which indirectly means the Actuator)?

One way is to keep track (memory) of total motion occurred and based on that, calculate the current rotor position. But in a system, with power reset and restart, this doesnt work I think.

Your comments please.

 

[KlausST]

Hi,

Usually you have three hall sensors giving a rising edge and a falling edge each per electrical revolution.
Giving a total of six events per 360° therefore your angular resolution is 60°.

The mechanical resolution depends on the count of magnetic pole pairs.

If you need better resolution you should consider an external angular encoder.

Klaus