The term "alternating-current motor" is often described as "AC motor" in short. Therefore, we will follow this convention in this book.
AC motors are roughly classified into commutator motors, synchronous motors, and induction motors.
Synchronous and induction motors are both AC motors whose rotating speed is determined by the rotating magnetic field.
Here, the rotating magnetic field refers to a phenomenon where the magnetic field that is generated by applying three-phase, two-phase, or other multi-phase alternating current to the stator winding rotates at a speed determined by the frequency of the multiple-phase alternating current (= synchronous speed). The rotating magnetic field attracts the rotor, causing it to rotate. AC motors are classified according to the difference in rotation method.
Rotating magnetic field AC motors (generic term for synchronous and induction motors) are roughly classified into motors that run on the 100 VAC (the power supplied to households via two-wire service lines), and motors that use 200 VAC power (distributed to factories, etc. via three-wire lines).
The former is called a single-phase motor and the latter a three-phase motor.
Of late, three-phase motors are more frequently driven by the power inverter circuit using a semiconductor device called an inverter. The objective of this driver configuration is to operate the motor at a rotating speed and torque intended for the application by controlling the voltage and frequency through use of the inverter.
-(1) Commutator Motor
Commutator motor is a generic description for motors using a commutator rotor as shown in Fig. 1.12. The type currently still in use in large numbers is what is called a universal motor (also called an AC series motor or an AC series wound motor).
The main application of this motor is vacuum cleaners, power tools, and juicers. In other words, it is used in areas where the motor is required to rotate at high speeds through the use of a single-phase AC power supply.
The word "universal" here implies that the motor rotates on AC or DC power supply (that is, an AC/DC motor).
In principle, it has the same structure as DC series motors, but the following points need to be considered when using alternating current:
<1> In the case of DC, the stator flux is constant, but in the case of AC, it changes. Therefore, it is necessary to reduce any eddy current generated by the changing flux with insulated core lamination.
<2> Drops in voltage were only caused by resistance in the case of DC, but with AC, in addition to drops in voltage caused by resistance, output is also reduced by the deteriorated power factor due to the phase shift resulting from electromagnetic induction.