Electrical Machines I PDF

Electrical Machines I UE22EE351A M.N.Viswanath Associate Professor, Department of EEE Electrical Machines I UE22EE351A BLDC Motors M.N.Viswanath Associate Professor, Department of EEE Electrical Machines I BLDC Motors (Introduction) Problem associated with PMDC Motor is t...

Electrical Machines I UE22EE351A M.N.Viswanath Associate Professor, Department of EEE Electrical Machines I UE22EE351A BLDC Motors M.N.Viswanath Associate Professor, Department of EEE Electrical Machines I BLDC Motors (Introduction) Problem associated with PMDC Motor is the commutation with the help of brushes ❖ In BLDC motors this problem is eliminated as they have no commutator and brushes. ❖ In BLDC motor the armature is stationary and permanent magnet field system is mounted on the shaft. ❖ Commutation is achieved by using semiconductor switches. ❖ BLDC motor can be treated as synchronous motor with permanent magnet rotor and d.c current is supplied to inverter which is automatically synchronized. Electrical Machines I BLDC Motors (Introduction) ❖ Performance wise, a BLDC motor in combination with auto synchronized inverter is exactly similar to a conventional d.c motor with the added advantages of elimination of mechanical commutator, brushes and electromagnets. ❖ Can be compared with induction motor drive up to 20 kW. ❖ Has higher efficiency, smaller in size and better cooling when compared with PMDC Motor. Electrical Machines I Classification Electrical Machines I Construction (Stator) Similar to that of a conventional induction motor. Core is made of steel stampings which are stacked together and fixed on the stator frame. The stator core has slots in the inner periphery to house the armature conductors. Closed or open type of armature windings are used. The armature winding is connected to the d.c source through suitable semiconductor switches. Electrical Machines I Construction (Rotor) Is made up of forged steel and carries permanent magnets. The armature should be wound for the same number of permanent magnets. For successful commutation , rotor position should be fed back. For this purpose, a sensor is to be mounted on the shaft. The sensor output is used to generate appropriate signals for switching power electronic switches in the inverter circuit that feeds the BLDC motor Electrical Machines I B L D C Motor Electrical Machines I B L D C Motors Permanent magnet can be fixed on the rotor in two different ways Surface mounted permanent magnet rotor:- Magnets are mounted on surface. In interior PM rotor the magnets are placed in grooves or slots. In interior PM rotor construction, even though the rotor appears to be of smooth cylindrical shape, magnetically it is projecting pole rotor. Function of permanent magnets is to provide necessary magnetic field Electrical Machines I B L D C Motors Surface mounted PM has speed limitations due to centrifugal forces. Advantages of interior PM Robust in operation, ability to operate at high speeds, high torque to ampere ratio and smaller effective air gap length Figure a)Surface ounted b) Interior Mounted Electrical Machines I B L D C Motors M.N. Viswanath Associate Professor, Department of EEE [email protected] +9880697030