When selecting motors, it is important to consider the requirements of the particular application. Servo motors have many advantages, which may make them more advantageous than induction motors.
1. More powerful and compact
One of the most obvious advantages of using synchronous motors is that they have a higher torque density than induction motors. Servo motors that are similar in physical size to induction motors usually produce more than 40-60% torque. This means that to achieve the torque, speed or power required for the application, a smaller, lighter servo motor than an induction motor is required. This makes permanent magnet motors ideal for applications with limited space and/or weight.
2. Low inertia, high dynamic response
Because the servo motor is more compact, it has lower inertia in essence compared with similar induction motors. Because of the small inertia, synchronous motors can accelerate and decelerate to/from their rated speed more quickly. It also allows more precise starting and stopping from full speed. This makes synchronous motors ideal for high dynamic or motion control applications.
3. Zero speed full torque
Another important advantage of permanent magnet motor is that it can continuously achieve full torque at zero speed. This is very different from most low-speed induction motors with limited torque and stability. VFD adjustments can be made for low speed operation (e.g. boost), but this generates additional motor heat and limits performance. Therefore, if zero speed holding torque is required, or if the application requires low speed operation, a servo motor (with feedback) is required.
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4. Higher IP level protection
In addition to the advantages of motor control, servo motors usually have advantages in their shell design. KEB synchronous motor does not need cooling fan and can reach IP65 protection level. On the other hand, induction motors are usually IP44 or IP54. Therefore, if the motor operates in a harsh environment, the servo motor may help prevent premature failure.
5. More and more economical
Finally, because servo motors have so many advantages over induction motors, you may ask why some people choose induction motors. The historical answer is that servo motors are much more expensive than induction motors. Although the servo motor is really expensive, the price gap has been narrowed. Synchronous motors with similar power specifications to induction motors can now be purchased at prices as low as 10-20%. In the past, the cost of servo motor may be twice or more than that of induction motor. As servo motors become more and more common, this price gap should continue to narrow.
One thing to note is that the induction motor can be powered from the line (fixed at 60Hz). Servo motors usually require servo drivers or amplifiers to run them. However, the driver has many other advantages, including accurate motor shaft performance, increased protection parameters and lower starting current.
