Reluctance Motor
Construction Stator –Single phase induction motor
Split phase reluctance motor Capacitor type reluctance motor
Rotor
Asymmetric magnetic construction By removing some rotor teeth
Operation It starts like an induction motor but runs with a small amount of synchronous torque. The synchronous torque is due to changes in reluctance of the magnetic path from the stator through the rotor as the slots align. an inexpensive means of developing a moderate synchronous torque. Low power factor, low pull-out torque, and low efficiency
Limitations Low Efficiency Low Power factor
Comparing one of the new synchronous reluctance motors, on the left, with the traditional type of A.C. motor on the right. Both motors deliver the same output power.
Applications Constant speed applications
Recording instruments Timing instruments
Switched Reluctance motor
Switched Reluctance motor
Variable reluctance motor drive waveforms: (a) unipolar wave drive, (b) bipolar full step (c) sinewave (d) bipolar 6-step.
Variable Reluctance Stepper Motor and Reluctance Motor A variable reluctance motor intended to move in discrete steps, stop, and start is a variable reluctance stepper motor high ripple torque desired in stepper motors. If smooth rotation is the goal, electronic driven version of the switched reluctance motor is to be used. a variable reluctance motor is optimized for continuous high speed rotation with minimum ripple torque
Switched Reluctance motor Construction The stator poles have concentrated winding rather than sinusoidal winding. Switched-reluctance motor operates like a variable-reluctance step motor However, the operation differs mainly in the complicated control mechanism of the motor. In order to develop torque in the motor, the rotor position should be determined by sensors so that the excitation timing of the phase windings is precise. Each stator-pole pair winding is excited by a converter phase, until the corresponding rotor pole-pair is aligned and is then de-energized. The stator-pole pairs are sequentially excited using a rotor position encoder for timing.
Construction…
Electronic driven variable reluctance motor
SR MOTOR CONTROL Measured Currents Speed Reference
Speed Regulator
Torque to Current
Current Regulator
PWM Generation & Synchro
Commutation Angles Advanced Angle Calc Speed Estimator
Power Hardware
SRM
Bus Voltage Position Measure
Advantages Simple construction- no brushes, commutator, or permanent magnets, no Cu or Al in the rotor. This simplicity of the motor compensates for the drive electronics cost. High efficiency and reliability compared to conventional AC or DC motors. High starting torque. Cost effective compared to bushless DC motor in high volumes. Adaptable to very high ambient temperature. Low cost accurate speed control possible if volume is high enough.
Disadvantages Current versus torque is highly nonlinear Phase switching must be precise to minimize ripple torque Phase current must be controlled to minimize ripple torque Acoustic and electrical noise Not applicable to low volumes due to complex control issues
Applications High volume applications like energy efficient vacuum cleaner motors, fan motors, or pump motors.
SRM driven compressor