By- Dr. -Ing Praveen Kumar
Within the earlier article, we had a have a look at the historical past of motors and their utility in early EVs, each on land and water. From the late nineteenth century onwards, motor expertise improved, particularly AC motors. In the present day we now have numerous varieties of AC motors reminiscent of induction motors, synchronous motors, brushless DC motors (BLDC), everlasting magnet synchronous motors (PMSM), switched reluctance motors (SRM), synchronous reluctance motors (SyncRel), to call a number of. In addition to these, we additionally hear about radial flux motors, axial flux motors, transverse flux motors and radaxial motors. And it doesn’t cease right here; there are multiport motors as nicely. Some years in the past, we did a venture within the e-mobility lab at IIT Guwahati and located that round 110 motor topologies are attainable. It is a big number of motors certainly, and it turns into a frightening downside when one has to decide on a motor sort for a given automobile platform and utility.
To make a even handed alternative, the vital query is, why is there such all kinds of motors, and is there an underlying thread uniting all these motors? Luckily, all these motor varieties and topologies will be simply defined utilizing the basics of physics, notably electromagnetism.
A wonderful level to start out is the precept of conservation of power. All motors and turbines are electromechanical power conversion gadgets, i.e., they convert the enter electrical power to mechanical power within the case of motors and vice versa within the case of turbines. We’ll, nevertheless, limit our dialogue to motors.
Since motors are power conversion gadgets, we evoke Émilie du Châtelet’s sacrosanct legislation of Conservation of Power. The assertion of this legislation is, as is the case with any nice theories of science, elegantly easy: “power can neither be created nor destroyed; slightly, it will possibly solely be reworked or transferred from one type to a different.” The sequence of occasions that occur in electrical motors on the backdrop of the Conservation of Power is as follows: enter electrical power will get transformed to magnetic power, and the magnetic power will get transformed to mechanical power. In a motor, two conversions occur, first from electrical to magnetic power and second from magnetic to mechanical power. Since no power conversion is ideal and is related to losses (loss is a type of power that we can’t put to meant use), the two-stage power conversion can also be related to losses (Determine 1).
The 4 loss elements, viz. Wohmic, Whysteresis, Weddy and Wfriction manifest as warmth that have to be extracted from the motor utilizing a cooling system. Mechanical power (W_mechanical) is the helpful work that the motor does. Determine 1 will be written down as an easy expression:
The above expression is legitimate for DC motors, AC motors, induction motors, synchronous motors, brushless DC motors (BLDC), everlasting magnet synchronous motors (PMSM), switched reluctance motors (SRM), synchronous reluctance motors (SyncRel), radial flux motors, axial flux motors, transverse flux motors, radaxial motors, twin port motors, or every other motor that we will conceive of. That is the primary unifying precept {of electrical} motors. The identical argument applies to turbines as nicely.
If all motors are similar with respect to the Conservation of Power, then what’s the distinguishing issue? The reply lies within the second conversion in Determine 1, which is magnetic power to mechanical power. To grasp it, we take a easy situation proven in Determine 2a to second.
Within the following passages, an argument is constructed, with out lack of generality, for the linear movement, and can also be legitimate for rotational movement.
Determine 2a has two bar magnets with reverse poles dealing with one another. On this case, if magnet 1 is moved to the proper at some velocity, say 1m/s, the second magnet shall be attracted in the direction of it and transfer on the identical velocity. Equally, if two bar magnets are positioned with the identical poles dealing with one another (Determine 2b), and we transfer the primary magnet to the left at 1m/s, then the second magnet shall be repelled and transfer on the identical velocity. What we now have seen in these two examples is the conversion of magnetic power into mechanical power. In these examples, two magnetic fields are concerned. Each magnetic fields work together with one another leading to a power that produces mechanical movement. This power is known as Interplay Pressure and will be engaging (Determine 2a) or repulsive (Determine 2b). One key statement is that each magnetic fields have zero relative velocity between them.
In Determine 2c, we now have the same scenario, however we exchange one magnet with an iron bar. If the bar magnet is moved to the proper at 1m/s, the iron bar shall be attracted towards it and transfer on the identical velocity. The notable distinction right here is that we now have just one magnetic area, and the power, on this case, is named the Reluctance Pressure. The Reluctance Pressure is at all times engaging in nature and therefore unidirectional, i.e., in Determine 2c, if we transfer the magnet to the left, then it’s not attainable to have sustained movement.
Additionally it is attainable to have a mixture of interplay and reluctance forces by modifying the geometry, as proven in Determine second. If the iron half is extra, then Reluctance Pressure dominates, whereas if extra quantity is taken up by the magnet, then Interplay Pressure is dominant.
That is the second underlying precept of all motors; they use both Interplay Torque (Pressure is for linear movement and torque for rotational), Reluctance Torque, or a mixture of each.
Within the configurations Figures 2a to second, we now have used everlasting magnets, however we will use electromagnets as an alternative. The attainable combos are proven in Determine 3. Moreover, we will use rare-earth-based everlasting magnets or ferrite magnets. All these potentialities give rise to completely different households of configurations and are listed in Determine 3.
On this article, we now have seen that despite the fact that there are differing types and configurations of motors, all share the identical underlying ideas, and the distinction lies in the kind of torque (Interplay or Reluctance or mixture of each) produced, the best way the magnetic area is created and the geometric development. Within the subsequent article, we are going to focus on completely different motor configurations and their suitability for EVs.
(Dr. -Ing Praveen Kumar is Professor, Division of Electronics and Electrical Engineering, IIT Guwahati. Views are private.)
