types of Motor windings can come in a variety of shapes and forms. However, three-phase distributed windings are most commonly used in AC motors for industrial applications, which is the focus of this article. The following instructions apply equally to the use of this type of winding in induction motors or permanent magnet synchronous motors.
The purpose of the distributed winding is to generate a sinusoidal distribution of magnetomotive force (MMF) in the air gap of the motor. This MMF occurs when a balanced set of three-phase AC current flows through the phase windings. This is an MMF, combined with the design of an automotive magnetic circuit, to generate a tsunami that travels across the air gap and produces the required motor torque.
The winding consists of several winding coils of insulated copper or,
in some cases, aluminum wire. Several strands of wire can be connected in parallel to form a single conductor, which can be wound into a coil and wound several times. The number of turns depends on your specific design requirements.
The distributed winding consists of several coils located in the groove of the motor stator, as shown below. The number of coils depends on the number of stator slots, the number of phases (3 in this case), and the number of poles on the motor.
Each coil spans several slots. Full-pitch windings have coils that correspond to a number of slots with an average spacing equal to pole pitch or 360 ° / p, but shorter speed windings spread to fewer slots. The following figure shows a typical 4-pole car full throttle winding.
4-pole motor stator with three-phase distributed winding
Part of the winding is in the groove that contributes to the generation of torque. The rest is the final turn, which does not contribute to torque generation. Therefore, careful design is required to avoid unnecessary waste of expensive copper. In addition, excellent thermal performance requires high slot filling and thermal control of the final winding. These factors are often limited by manufacturing process considerations. An ideally distributed winding has an infinite number of coils arranged in an infinite number of slots so that the MMF spatial distribution is a perfect sine wave. This is clearly not possible in practice, so you need to find the best compromise to meet your performance needs.
Coil of different phases should be separated from each other and from the stator core to avoid short circuits and failures. Insulation provides an additional thermal barrier that limits the ability of the machine to transfer heat from the inside to the outside. There is an air gap between the windings and between the insulator, windings and stator core. These gaps are filled with resin by a fertilization process that improves heat transfer and further improves the insulation of the windings.
Electric vehicles have a wide variety of uses.
Different applications impose different requirements on car design. Some of these requirements are influenced by the winding design and may include:
Minimize harmonic loss to improve efficiency
Reduce torque pulsation reduced acoustic noise and vibration.
Multiple winding designs are possible to achieve the same electrical performance. These design choices are determined by manufacturing constraints that are strongly influenced by the level of automation used to manufacture the windings.
The following table lists some of the most common winding configurations and the main selection criteria.