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Difference b/w Simple DC motor and Brushless DC motor

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kashif9744

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brushless dc motor transfer function

Hi,
Can any body tell me Is there any difference b/w the mathematical model of simple DC motor and Breshless DC motor,if Yes then what is the mathematical model of Brushless motor
 

dc motor inrush current

Hi,

From a mathematical point of view, if you're only interested in a very rough model, you can describe both types of motors with similar equations (U=r.i + L.di/dt + K.EMF and Torque = K.i and EMF = K.speed). Both machines work in a similar way, the mechanical commutations of the brush motor being translated into electronic commutations of the inverter. However, if you're interested in the detailed electrical behavior of the motors, you'll have to implement a much more complex model.
I hope this helps,

Samuel
 

difference b/w brush motor & brushless motor

Hi,
I want to ask about the tranfer function of BLDC motor
 

bldc motor inrush current

It's also said when a motor is runned from a dead stop, it consumes 10 times more current than rated current.So how could we define this phenomena by mathematical model of motor and also I haven't seen any motor equations which defines such inrush current.
 

bldc motor equations

Hi gentlemen,

The transfer function of the motor from voltage to torque is that of an RL circuit with the addition of the back emf. After that, an integrator with gain (inertia) and the subtraction of the load torque will give you the machine speed, which you can feed back to get the back emf.
Look at P. Pillay and R. Krishnan: "modelling, simulation, and analysis of permanent magnet motor drives, part II: the brushless DC motor drive", IEEE IAS transactions.

The inrush current you mention is due to the lack of back emf at startup. If you start with full voltage you will basically get a large voltage applied to a low impedance and therefore a large current. If you're using PWM you can ramp up the voltage and therefore the current and avoid the inrush.

Samuel
 

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