Working principle diagram of single-phase AC motor

Working principle diagram of single-phase AC motor

The working principle of single-phase motor controllers is based on the switching operation sequence of certain power switches, namely thyristors. The thyristors are switched on in such a way that the load is connected to the AC power supply during a part of each half cycle of the input voltage. Therefore, the output voltage follows the part of the input AC voltage to which the load is connected to the power supply. In this way, the output voltage is controlled.

Single-phase motor controller

When the stator of a single-phase motor controller is powered by a single-phase power supply, it generates an alternating magnetic flux in the stator winding. According to Faraday's law of electromagnetic induction, the alternating current flowing through the stator winding generates an induced current in the rotor bars (of a squirrel cage rotor). This induced current in the rotor also generates an alternating magnetic flux.

Even after setting the controller to two alternating fluxes, the motor still cannot start. However, if the rotor is initially started by an external force in either direction, the motor accelerates to its speed and keeps running at its rated speed. This behavior of single-phase motors can be explained by the double-field rotation theory.

Types of Single Phase Induction Motors Single phase induction motors are widely used in applications where only single phase power is available. These devices are manufactured in the range of several kilowatts to meet the requirements of various applications such as ceiling fans, food mixers, refrigerators, vacuum cleaners, portable drills, hair dryers, etc. The various types of single phase induction motors are briefly discussed below. Based on the starting method, the basic types of single phase asynchronous motors are split phase motors, capacitor start motors, permanent magnet capacitor run motors, etc.

The split phase induction motor is one of the most widely used types of single phase induction motors. The main components of a split phase motor include the main winding, auxiliary winding and centrifugal switch. It is a simple arrangement to establish a rotating magnetic field by providing two windings on the same stator core. The auxiliary winding or the starting winding has a series resistor so that its impedance becomes highly resistive in nature. It is wound differently from the main winding but has fewer turns and a much smaller diameter than the main winding.

Capacitor start induction motor is similar to split phase motor but a capacitor is connected in series with the auxiliary winding. This is an improved version of split phase motor. Since capacitor absorbs leading current, use of capacitor increases the phase angle between the two currents (main and auxiliary) thus increasing starting torque. This is the main reason for using capacitors in single phase induction motors.

Working Principle of AC Synchronous Generator

The working process of an AC synchronous generator can be simply viewed as the working process after the commutator device in a DC generator is removed, that is, there is no commutation process during the rotation of the generator rotor winding, and the current output direction changes.

In addition, in an AC synchronous generator, it is not the rotor winding that cuts the magnetic flux lines, but the rotor that generates a rotating magnetic field (the excitation device passes current into the excitation winding), which makes the stator winding cut the magnetic flux lines, thereby generating an induced electromotive force, which is led out through the terminal. Figure 6 shows a schematic diagram of the working process of an AC generator.

The AC synchronous generator can be designed to generate single-phase or multi-phase AC voltage according to the number of output phases of the stator winding. Figure 7 shows the basic settings for generating single-phase, two-phase and three-phase AC voltage.

Figure 8 shows a schematic diagram of the working principle of a single-phase AC generator. When the magnet rotates, a sinusoidal AC electromotive force e is generated in the two stator windings A and B. The power source that generates the electromotive force is called a phase. This type of generator uses an AC supplied by a single phase and two wires, which is called a single-phase AC. This distribution method is called a single-phase two-wire system.

In this type of generator, three stator windings AX, BY, and CZ with the same structure are placed in the stator slots, where A, B, and C are called the beginning of the windings, and X, Y, and Z are called the end of the windings. These windings are spaced 120° apart in space. The rotor magnetic field is distributed in space according to the sinusoidal law. When the rotor is driven by the prime mover to rotate clockwise at a constant angular velocity ω, three sinusoidal electromotive forces with the same frequency, equal amplitude, and 120° phase difference are generated in the three stator windings, thus forming a symmetrical three-phase electromotive force.