If before we had to choose between diesel and gasoline, and each one had its supporters and detractors, the arrival of the electric car leads us to a similar dilemma, having to differentiate between the asynchronous motors and synchronous motors. That is why it is important to know them, whether you are a fan of the world of cars or if you are really interested in buying an electric car and do not know where to start. What is a synchronous motor? What advantages does it have? What models of electric cars carry one of these motors today?
Synchronous motors are widely used by manufacturers when a lot of power is needed in a small motor. However, the difficulty in obtaining magnets keeps them as an option to avoid.
What is a synchronous motor
A Synchronous motor is an electric motor in which the magnetic field of the stator and the rotor rotate at the same speedd, synchronously.
That said, let’s try to explain it in a slightly more accessible way. An electric motor has two main components, a stator and a rotor. The stator is the outer, largest and most visible part of the motor. It is static, it does not move. The rotor, on the other hand, is a moving part, and it is rotating, hence its name. The rotor usually goes inside the stator.
The function of an electric motor is to convert electrical energy into kinetic energy or motion. The stator is connected to the electric battery, while the rotor is connected to the car’s transmission and thus to the wheels.
The basic operation of an electric motor is that of create a magnetic field rotating in stator. The stator does not move, but the magnetic field does, as we will explain below. A) Yes, the rotor, which is also magnetized, follows the magnetic field of the stator just as it happens with a compass when we bring a magnet close to it. Since the rotor is “connected” to the wheels, we have managed to convert electrical energy into movement.
As we said, In synchronous motor, the rotor is synchronized with the stator field and they rotate at the same speed.
How a rotating magnetic field is generated in the stator
It would be good if you took a look at the specific content in which we explain in detail what is the stator. But in a simplified way we will say that the stator has coils spread around the perimeter. These are fed sequentially and triphasically. When an electric charge passes through a conducting material, a magnetic field is generated around it. Controlling which coils are powered at each moment we generate a rotating magnetic field. The idea is that said magnetic field varies its magnetic north and that it rotates, as if it were going through each of the clock hands. Thus, the rotor, which is also magnetic, will follow this magnetic field.
Types of synchronous motors
There is a factor that we have not clarified, and that is the rotor. We have said that it is magnetic. But there are two types. A good option to make a simple magnetized rotor is install permanent magnets in the rotor, so that it is naturally magnetic. These permanent magnets are becoming more difficult to obtain, so in the long run they would not be an interesting option for many manufacturers. That is why an alternative is sought, such as using electromagnets. Just as a magnetic field can be created in the stator by powering electrical coils, so can install electrical coils on the rotor and feed them electrically to magnetize it.
In this way, we have two types of synchronous motors: permanent magnet synchronous motors Y externally powered synchronous motors. The name of the second is due to the fact that while in the first the rotor is a part without power, in the second the rotor must be electrically powered to magnetize it. Once this is understood, it is very easy to understand the advantages of each one.
Advantages and disadvantages of synchronous motors
A basic advantage of synchronous motors, whatever the type, is that we have a direct relationship between the magnetic field that we generate in the stator and the movement that we can bring to the wheels. This simplifies the development process of synchronous motors. In addition, it allows you to work with lower stress levelsthus avoiding overloads that could cause damage to components or even danger to users.
Also, we have a motor that stands out especially for its power delivery. And it is that once we have managed to start the rotation of the engine, we have maximum performance. That is why this type of engine has shone a lot in some sports models.
However, from the hand of the above we also have that we will spend more energy to start the movement of the carbecause we have to overcome the barrier in which the magnetic field has no strength to start the rotation of the rotor.
Specific advantages and disadvantages of the permanent magnet motor
The permanent magnet synchronous motor it is somewhat different from the externally powered motor, and hence has its own advantages and disadvantages. In favor we have the fact that the engine has a more basic operating principle. By having a rotor that has a natural magnetization, we forget about all the paraphernalia around the rotor that other motors imply. Fewer components, a smaller motor, less wear and tear, and high reliability as well as zero vibration.
They are practically all advantages if it were not for the fact that we find the Difficulty getting these magnets, being the extraction and production of the same highly concentrated in China, and also having a relatively limited amount of these. Its price has become more expensive and it is not a good option for the future.
Specific Advantages and Disadvantages of the Externally Powered Motor
If we don’t have permanent magnets for the rotor, we have to create an electromagnet. To do this, we need to install coils on the rotor, which involves a bigger size for both rotoras for the stator itself that “contains” it, as well as weight problems. On the other hand, we have to also connect the rotor to the battery. This implies the need to use brushes to be able to feed an element that is in rotation. All this is one efficiency loss. On the one hand, we spend energy to power the rotor that we do not spend with the permanent magnets, which translates into less autonomy. On the other hand, the brushes produce some friction, which somehow slows down the motor. And there are also more vibrations.
And of course, friction implies wear. The brushes are usually made of noble metals, with a good composition of gold. Having to change them will be funny to the owner when he sees the bill.
What cars use synchronous motors on the market
Tesla was one of the main proponents of asynchronous motors. And it is possible that from time to time we will see that it is the path followed by many other brands. Nevertheless, for the Tesla Model 3 a permanent magnet synchronous motor was chosen. This is for its efficiency and performance. With less energy, this motor generates more power, which is beneficial when we are still limited by battery capacity and range. In fact, it also includes permanent magnet motor in the front of the Tesla Model X and S, because in heavier cars there are even more notable benefits in the use of these engines. However, it must be said that these last two, as in the case of many cars on the market, we find the two types of engines, since the advantages of each of them are used depending on the case. You only step on the accelerator, but the car driver does the rest.
Many brands opt for permanent magnet synchronous motors when they have to simplify, need autonomy, or have space problems. For example, most hybrid cars have permanent magnet motors. They need to be smaller to integrate with the combustion engine, and it is the ideal solution. We see it in the case of Toyota, Audi or Mercedes, for example. However, brands such as Audi or Mercedes do not integrate these motors in their 100% electric versions, where they are looking for a longer-term option, or where they have the possibility of housing a larger motor and battery.
Instead, when the manufacturer seeks maximum performance, it also opts for permanent magnet motors, as is the case with Porsche. Here the greatest possible power is sought according to the weight of the motor, and this is achieved with permanent magnet synchronous motors. It is also true that the units sold of these vehicles are much less, which makes it easier to use a component that is difficult to obtain.
On the other hand, externally powered synchronous motors are not very common. We have a main representative, as is the case of the Renault Zoe. The brand claims that the brushes and the entire motor block have a useful life as long as the vehicle itself. Of course, if time proves them right, we will have a most interesting engine. Although other brands, such as BMW, have already developed engines with this technology and it remains to be seen exactly what will happen in the future.
However, it must be said that the long-term path probably goes through asynchronous motors or induction motors, thus dispensing with hard-to-find magnets. Although this will happen the day the way is found to get greater autonomy with batteries of the same size.