ELECTRICAL MACHINE DESIGN SWITCHED RELUCTANCE MOTOR
SWITCHED RELUCTANCE MOTOR (SRM):
The SRM is a special electrical machine. The special machines are constructed for some specific applications.
SRM is electromagnetic and electrodynamic equipment which converts the electrical energy into mechanical energy. The electromagnetic torque produced on variable reluctance principle. SRM make use of
- Power semiconductor switching circuitry and
- Rotor position sensor.
SRM is singly excited and doubly salient electrical motor. It has salient poles on both the rotor and stator but only one member carrying windings. The rotor has no windings, magnets and cage winding but it is build from a stack of salient pole lamination.
The stator is made up of silicon steel stampings with inward projected poles. The number of poles of stator can be either an even number or an odd number. Most of the motors available have an even number of stator poles (6 or 8). All these poles carry field coils. The field coils of opposite poles are connected in series such that their mmf’s are additive and they are called phase windings. Individual coil or a group of coils constitute phase windings. Each of the phase windings are connected to the terminals of a power semiconductor switching circuitry, whose input is dc supply.
The rotor is also made up of silicon steel stampings with outward projected poles. Number of poles of rotor is different from the number of poles of the stator. In most of the available motors the number of poles of the rotor is 4 or 6 depending upon the number of stator poles 6 or 8.
The rotor shaft carries a position sensor. The turning ON and turning OFF operation of the various devices of the power semiconductor circuitry are influenced by the signals obtained from the rotor position sensor.
BLOCK DIAGRAM OF SRM:
DC supply is given to the power semiconductor switching circuitry which is connected to various phase windings of SRM. Rotor position sensor which is mounted on the shaft of SRM provides signal to the controller about the position of rotor with reference to the reference axis. Controller collects this information and also the reference speed signal and suitably turns ON and OFF the concerned power semiconductor device of the switching circuit such that the desired phase winding is connected to the dc supply. The current signal is also fed back to the controller to limit the current within permissible limits.
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