What Is A Switched Reluctance Motor?

A switch reluctance motor is a kind of a speed regulating motor that is developed after the development of the DC motor and the brushless DC. The power level of the product can vary from several watts up to a range of hundreds of kilowatts. They are seen to be used in various different applications whether they are household applications, aviation related applications, aerospace applications, electronic applications that include electric vehicles, machinery etc.

How Do They Work?

In the case of the switch reluctance motors, there is a switch that is specifically used in the speed control system of switch reluctance motors. The control system is the part that actually realizes the energy conversion from electrochemical energy to the SRD. It is also a sign that suggests that suggest that SRD is quite different from the other types of motor driven systems that exist. The switch reluctance motors have a double salient pole, the stator and the rotor which are laminated using the ordinary sheets of silicone that are of steel. And the rotors of this SRM neither have windings nor do they have any sort of permanent magnets. The concentrated windings over the stator poles are just like the wounds over them. 

There are two poles that are connected together with the help of diametrically opposed winding which is called one phase. When it comes to the SR motors, they can be designed with a variety of different types of phase numbers, the stator and the rotor have various different types of poles. In order to reduce the torque ripple, this large number of phases and a large number of small step angles is highly beneficial, but the structure is quite complex as the main switching devices are quite large in size and they cost high too. However, nowadays the structures that are more likely to be seen are four phase structures and six-phase structures. To add on the magnetic flux always closes along the path of the least reluctance and as the iron core with a certain shape moves to a position with minimum reluctance making its main axis and the magnetic field. The axes coincide with each other. 

Advantages Of Reluctance Motor Mechanism  

1. A Simpler Structure

When it comes to the SR motor, it is seen that the structure is quite simpler, low in terms of cost and can be used for operations that are based on high speed. The structure is said to be as simple as that of a squirrel cage induction motor. The rotor is said to have extremely high mechanical strength that is ideal to be used for operations that are based on ultra-high speed (this is around tens and thousands of revolutions per minute). When it comes to the stator there are only a few concentrated windings thus it is easy to manufacture and simpler in the terms of insulation structure. 

2.Reliability Of The Circuit 

This type of circuit is the power circuit that is much simpler and much more reliable this is because the motor torque direction has nothing to do with the winding that is in the direction of the current which is only a single-phase wiring which is used when current is needed so that thee power circuit can achieve more than one power switch per phase. On the other hand, when it comes to the windings of asynchronous motors there needs to be a flow of bidirectional currents.

Therefore, when it comes to the speed of the switched reluctance motor speed control system, it only requires fewer components of power compared to the PWM frequency circuit as the circuit structure is quite simpler. In addition to it, there are around two power switch tubes that are there in each arm of the bridge arm of the PWM inverter power circuit that is exactly across the side of the DC power supply which is prone to short circuits and burning power devices. In the system of the switched reluctance motor speed control speed, each of the power switch devices is directly connected in the form of the series with the winding of the motor that basically is done to avoid the phenomenon that happens through short circuit.

3.Reliability Of The System

The reliability of the system is high. When seen from a perspective of the electromagnetic structure of the motor, each type of winding and each type of magnetic circuit of the motor are not dependent upon each other anyhow and each generates an electromagnetic torque that is seen to happen within a certain axis and range of angle. Unlike in the case of the General Motors where a rotating magnetic field is generated under the action of each phase of winding and the magnetic circuit so that the motor can operate normally. Observing the control structures point of the view, each of the circuits of the phase supplies power to the winding phase and works without being dependent on each other. 

4.The Starting Advantage

It is also seen to be beneficial while starting as well, as large starting torque is produced and the starting current is quite low as the controller outputs less current and the motor is said to get a larger starting torque. this is one of the major and the most admired feature of this system. The data of a typical sort of a product is stated to be as 15% when the current is starting, the starting torque would be 100% rated torque, however when the starting current is 30 % of the rated current, the starting torque would have a potential to reach up to 250% of the rated torque. 

5.Frequent Start And Stop 

The SRM is also considered a suitable option for the frequent start, forward and reverse conversion operations as this system is designed in a way that it has characteristics of high starting torque and the low starting current thus the current impact is small during the starting process.

Disadvantages

1.A large torque ripple is observed.

2.There are also complaints of noise and vibration.

3.From the working principle, the torque generated on the rotor of the switched reluctance motor is overlaid by pulse torques, which overall affects the performance of these SRMs.