‘Virtual magnet’ claims reveal why EVs need their rare-earth magnets
There have been a number of news reports recently about a startup in Bengaluru called Vimag Labs that has reportedly replaced rare-earth magnets in motors
There have been a number of news reports recently about a startup in Bengaluru called Vimag Labs that has reportedly replaced rare-earth magnets in motors with so-called “virtual” magnets. One such report quoted Manish Seth, the start-up’s CEO, as saying: “We remove permanent magnets, replace them with copper coils, and then through software, we generate magnetic fields inside the motor.” To understand this claim, it helps to first see how electric motors produce magnetic fields and why they use permanent magnets in the first place. Rotor and stator A motor needs a magnetic field to operate. One way to create it is using a permanent magnet. Another is to pass current through copper coils that have been wound around a ferromagnet, temporarily turning it into a magnet. This is called an electromagnet — and it is this approach that the startup has used, instead of permanent magnets. When an electrical machine converts electricity into mechanical motion, it is called a motor. On the other hand, a machine that converts mechanical movement into electricity is called a generator. In both cases, the conversion happens via a magnetic field. In a motor, for example, mechanical energy is harvested when the electric energy is used to rotate a component called the rotor. In a generator, electricity is harvested through conductors embedded in a stationary component called the stator. You can imagine both the stator and the rotor to be two concentric cylinders. Most of the time, the rotor is the inner cylinder. And the magnetic field is established in the gap between the stator and the rotor for the energy conversion process to happen.
An old technology This is how the large generators in hydroelectric, thermal, and nuclear power plants work. And for a long time now, they have used electromagnets instead of permanent magnets. In these generators, a turbine spins the rotor. In a thermal or nuclear power station, the turbine is driven by steam. In a hydroelectric power station, it is driven by falling water. The rotor rotates at a fixed speed to generate an alternating current (AC) of frequency 50 Hz. The rotor has copper coils wound around its ferromagnetic core. When these coils are supplied with a direct current (DC), they create a magnetic field, and the core acquires a magnetic north and a magnetic south pole. And as the rotor spins, this magnetic field sweeps past the stator windings, inducing an alternating voltage in them. This helps convert mechanical power into electricity. This technology has been around for 135 years. The next question is how electricity can be fed continuously into coils that are themselves rotating. Enter: the brushless excitation system. The rotor coils need DC — but supplying it through sliding electrical contacts is difficult because the rotor is constantly spinning. The solution is to mount a rectifier, a device that converts AC into DC, on the rotor itself. To this rotating rectifier, an AC is supplied from another generator. And this other generator is coupled to the same shaft of the turbine imparting mechanical power to the main generator. Software and magnetism This is essentially the principle behind the start-up’s “virtual” magnet: software regulates the current flowing through the electromagnets, thus controlling the strength and direction of the magnetic field.
The BriefWire