The switched reluctance motor (SRM) operates on the principle of variable reluctance, producing torque when its stator and rotor poles are configured so the magnetic reluctance is minimized. It consists of a silicon steel stator with inward projecting poles and a rotor position sensor. The SRM can operate in three modes: constant torque mode below a base speed, constant power mode above base speed using angle control, and torque proportional to speed squared at maximum speeds like a DC series motor. Torque production is based on current flow in the stator creating flux linkage, with the highest torque occurring when stator and rotor poles are aligned.

1. Switched Reluctance
Motor (SRM)

3. Introduction
 Switched reluctance motor (SRM) is electromagnetic and electrodynamics
equipment which converts the electrical energy into mechanical energy.
 The electromagnetic torque is produced on variable reluctance principle. SRM
makes use of
Power semiconductor switching circuitry
Rotor position sensor

4. Construction
 The stator is made up of silicon steel stampings with inward projected poles.
The number of poles of the stator can be either an even number or an odd
number.
 Most of the motors available have even number of stator poles (6 or 8).

6. Principle of operation

8. Block Diagram of SRM

9. SPEED TORQUE CHARACTERISTICS OF
SRM and Modes of Operation

10.  Figure 4 describes the three basic modes of operation of switched reluctance
motor based on the torque-speed characteristic.
 Currents in the stator circuits are switched on and off in accordance to the
rotor position.
 With this simplest form of control, the switched reluctance motor inherently
develops the torque speed characteristics typical to that of a DC machine.
 The drive operates in current control mode up to base speed ωmb, providing
maximum constant torque, thus giving constant torque mode.
 Above base speed, the drive operates in angle control mode. With a fixed
value of conduction angle, torque is proportional to speed squared. By
increasing the conduction angle with speed, the drive can be operated in
constant power mode.
 When maximum conduction angle is reached at speed ωmp, the motor
operates with its natural characteristics where torque is proportional to speed
squared and therefore, maximum available power reduces inversely with
speed like a dc series motor.

11.  The drive is operated in closed-loop with outer speed loop and inner current
control loop, as shown in Fig. 5. Depending on the speed, the drive is
operated in current control mode or angle control mode.
 Depending on the sign of speed error the drive is operated in motoring or
braking mode.

12. Torque Equation
 Consider the phase winding excited by a voltage source of voltage v. Then
where i is the current through the phase winding, R the resistance of the phase
winding and ψ the total flux linkage of the phase winding.
Substituting ψ = Li in Eq.3.1

13. where ωm = rotor speed in radians/second.
 The term ωm i(dL/dθ) is the phase winding back emf e given by the following
equation
The back emf is a function of i, ωm and (dL/dθ). The instantaneous electrical
power input to the machine is given by

14. where T is the instantaneous value of developed torque.
 The instantaneous power supplied to the machine, vi, is utilized to provide
the following:
 winding heat loss, Ri2
 rate of change of the stored magnetic field energy, d/dt (1/2 Li2)
 the mechanical power output
 From Eqns. (3.7) and (3.8), the motor torque is given by