Reluctance Motor

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