PMSM versus BLDC - Which motor powers your Electric Car better?

Together with electric batteries and controller systems, the electric motor forms the heart of an electric vehicle (EV). An electric motor converts electrical energy into mechanical energy to propel the electric car. While  designing an electric vehicle, automobile manufacturers in India and across the world have to keep an eye on the size, weight and aerodynamics of the electric car to select the right electric motor. There are many variables such as speed, torque and power requirements to consider before fitting the right motor because it affects the performance of the car.

The early electric vehicle models in India were fitted with Brushless DC motors (BLDC). The  BLDC motor is known as an advanced version of a Brushed DC motor . It has two major parts - a rotor and a stator. The rotor is the movable part that has permanent magnets known as the rotor magnets. The stator is the stationary part made up of coil windings. When electric current passes through the stator’s coil windings, it generates a magnetic field and rotates the permanent magnets of the rotor. By varying the current flowing through the stator, the speed of the motor can be controlled. Due to the absence of brushes, this electric car motor has the ability to work at a higher speed, produce constant torque and eliminate sparks in the electrical system of the car. It is durable and has an excellent ability to respond and control the mechanisms of the electric vehicle at high speeds. The BLDC motor also has a power-saving advantage derived from its ability to self-start. Automotive manufacturers resort to using BLDC motor controller solutions to give drivers the ease of motor control. 

However, the latest electric cars in India come with the Permanent Magnet Synchronous Motor (PMSM). These are seen as an alternating current (AC) counterpart of the Brushless DC motor and a better alternative to the AC Induction Motor. The permanent magnet synchronous motor is a device that uses permanent magnets embedded in its steel rotors to create a constant magnetic field. The stator carries windings connected to an AC supply which produces a rotating magnetic field. Then, at synchronous speed (where the phase difference is zero and the frequency is same), the rotor poles lock with the rotating magnetic field. Neodymium magnets are the most commonly used magnets in this electric car motor.

Though  the working of the PMSM is quite similar to the BLDC motor, there are some major differences in the performances of the two. In the BLDC motor, the rotor position is detected by a set of three hall effect sensors which result in small breaks during reversing the direction of the current. This can cause torque ripples which decrease the torque output of the motor. In contrast, the PMSM requires only one hall effect sensor, thus the commutating of currents remain continuous and the torque ripples are eliminated. The nature of the drive current in PMSM is sinusoidal in nature, which means it deploys alternating current and reduces the overall noise produced by the motor. This is why the latest electric car manufacturers in India prefer PMSM over BLDC motors to achieve the best performance.

Permanent magnet synchronous motors have proven to be more efficient than BLDC motors. This motor has the ability to maintain full torque even at low speeds. It not only has a low maintenance cost but the heat generation is also less in comparison to a BLDC motor. This is because the PMSM only has a stator winding and the rotor does not have any coils, thereby increasing efficiency. The heat transfer from the motor to the battery and other parts is better and the cooling system is simple. The high-power density and smaller size of the PMSM makes it an ideal choice for a compact mechanical package in electric cars. One  of the latest electric cars in India, the Tata Nexon EV, also uses a permanent magnet synchronous motor powered by Ziptron technology for an unparalleled experience.

With electric cars making rapid advances in the Indian automobile market, it is imperative for one to stay up-to-date with the latest developments in electric cars and their components. This will prove to be crucial while making an informed decision in the long run.

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