What Are Motors?
AC Servo Motor
Just like motors that operate on DC power supply are called DC motors, those that operate on AC power supply are called AC motors.
Motors that are called AC servo motors are classified into induction motors and brushless DC motors.
Why are brushless DC motors called AC motors? This is because the alternating voltage that changes over time is applied to the coil of a rotating brushless DC motor.
The name brushless DC motor comes from its principle of rotation, namely it is a DC motor without a brush. Meanwhile, the name AC motor comes from the type of driving power.
There are two ways of driving brushless motors, namely square wave drive and sine wave drive. There is also another approach that has been recently employed. This approach tries to enhance motor performance by using a waveform that falls between sine waves and trapezoidal waves.
Some companies insist that sine waves alone should be defined as AC waveforms, but others argue that square waves and trapezoidal waves should also be included. There is no unified view about this.
In the current situation, it seems you might well think that AC servo motors are "not brush DC motors".