The difference between concentrated winding and distributed winding of motor

The winding is always wound over at least two stator teeth. In concentrated winding, one stator tooth is wound. Both types of winding have different advantages and disadvantages.

When to use concentrated windings and when to use distributed windings depends on the dimensions of the motor and its application.

The motor production target and how the motor is manufactured also have an impact on the choice of winding type. Other distinguishing features that are important to winding design are fractional slot winding versus integer slot winding, and single layer winding versus double layer winding.

Motor winding diagram

（Motor Winding Diagram）

Concentrated winding, one stator tooth carries exactly one winding. Different colors represent the three phases U, V and W. The two windings of one phase are connected to each other, and then the three phases can be connected in star or delta.

In distributed winding, at least two teeth are wound, as shown in this example. The number of teeth wound is called the coil span, and of course 3, 4, 5 or more teeth can be wound. The coil span depends on the number of teeth in the stator and the number of pole pairs in the rotor.

Concentrated winding

(concentrated winding)

With concentrated windings, the stator is always wound on exactly one tooth. This has significant advantages in manufacturing the stator. For example, the finished windings can simply be pushed onto the stator. But the design of the stator's teeth must be specially designed for this.

What is the technical difference between distributed winding and concentrated winding. For this we will study the voltage of the back EMF. Measure voltage at the terminals of a motor with permanent magnets when the motor is spinning fast enough. The rotation of the motor can be measured by hand or with a load machine.

In motors with a classical design and concentrated windings, the back EMF is trapezoidal. Therefore, this type of winding can generate high torque, especially in the low speed range.

However, this does not mean that it is efficient. This is because the main disadvantage of concentrated windings is the generation of harmonics, which can lead to high losses, especially at high speeds. These losses can occur in the windings in the laminations and in the permanent magnets.

Concentrated windings are mainly used for short motors with large diameters. For example, wheel hub drives without gears. Concentrated windings are also used for drives that require high dynamics and where efficiency is not so critical.

Another disadvantage of concentrated windings is torque ripple, but this can be compensated, for example by moving the magnets relative to each other on the rotor or by shaping the magnets accordingly.

Distributed winding

(Distributed Winding)

In distributed windings, the winding heads are larger due to the overlap of the windings. Due to the smaller winding heads of concentrated windings, the ohmic losses in the low speed range are lower than in distributed windings.

For distributed winding, at least two teeth of the stator are wound, as shown in the example in the figure. The number of teeth wound is called the coil pitch or step size, and of course 3, 4, 5 or more teeth can be wound.

In distributed windings, the windings overlap at the top and bottom of the motor. This area of ​​the motor is also called the winding head. Due to the overlap, the winding heads in distributed windings are larger than those in concentrated windings. Therefore, for very short motors, concentrated windings are often used instead of distributed windings. The ohmic losses in concentrated winding heads are smaller. For longer motors, the losses in the winding heads do not contribute much to the total losses.

A very important advantage of distributed windings in motors is that the generated back EMF has a smooth mostly sinusoidal characteristic. This means that the proportion of harmonics is very low and the losses in the stator and winding laminations are also smaller. Distributed windings are used in applications that require higher efficiency, such as electric vehicles.

Another advantage of distributed winding is high synchronism, which means that torque ripple and noise of the motor are very low. Therefore, distributed winding motors are mainly used in rotary spindles of machine tools, otherwise torque oscillations will have a negative impact on the quality of the machined workpiece.