Question

14

The torque generated by a PMSM by, is the (positive) magnitude of . If we control the angle  such that  , hence ,  then the PMSM becomes a Field Oriented Control BLDC motor generating the torque as .   On the other hand, the torque generated by a separately excited dc motor can be expressed by  (refer to lecture notes).   For permanent magnet DC motor, .

1.1      BLDC vs SEDC

Describe in detail terms how   and   are similar.  (Which term corresponds to which).

1.2      BLDC vs PMDC

Describe in detail terms how   and   are similar.   

1.3      PMSM vs PMDC

Explain the difference between   and  .    Explain why we don’t refer PMSM as a BLDC or DC motor.  

Answer 1

Advantages of SEDC motors.

1.simple construction

2. low maintainence

3.less price

4.highly reliable motor and thus it is beging used extensivle by automotive industry.

PMSM

Permanent Magnet Synchronous Motors are similar to (BLDC).

2>> Sinsiodal flus in air gap.

3>> Construction of rotor and sstator gives low intertia thus smother operation .

4>> size is less and highly efficent device.

Advantages of Brushless DC Motor

1. BLDC is high efficient motor its speed depends on frequesncy at which current is given not a function of voltage.

2.Brushes are not present hence mechnical friction losses are less , makes this machine highly efficient.

3.High speed operation is possible.

4.No spraking and reduced level of noise.

5. inertia of BLDC rotor is low makes it quick accerelarate and deaccerelarate.

Disadvantages of Brushless DC Motors

1. Cost is high.
2. power supplied has limitation.

Advantages of Permanent Magnet DC Motor or PMDC Motor

They are :

1.feild excitation is not required as permanent magnet is beging used.

2.No excitation feield power consumption hence efficency of machine increases.

3. reduced size due to no feild winding.

4. Cost is less.

Disadvantages of Permanent Magnet DC Motor or PMDC Motor

1.

Field is fixed in the airgap thus speed control is not that good as in other motors.

>>> posiblity of effeft of armature reaction is high here.

>>pole damage is frequent