Single-phase AC motors are a common type of electrical equipment in various industries. The vast majority of motors powered by the main power source for household or light industry are single-phase. One of the keys is to select the correct motor size according to the application. Most motor control applications require speed control of single-phase induction motors because it not only provides variable speed, but also reduces energy consumption and audible noise. The article will mainly introduce the relevant knowledge of single-phase motor controller.
Single-phase motors are widely used in homes, offices, factory workshops, etc., because the power delivered to most houses and offices is single-phase. In addition, single-phase motors are reliable, low-cost, simple in structure and easy to maintain.
Most single-phase induction motors are unidirectional, which means they are designed to rotate in one direction. By adding additional windings, external relays and switches, or by adding a gear mechanism, the direction of rotation can be changed. Using a microcontroller-based control system can add speed changes to the system. In addition to the speed change option, the direction of rotation can also be changed, depending on the motor control algorithm used.
Working principle of single-phase motor controller
The working principle of the single-phase motor controller controller is based on the switching operation sequence of some power switches, that is, the thyristor. The way the thyristor is switched on allows the load to be connected to the AC power supply during a portion of each half cycle of the input voltage. Therefore, the output voltage follows the input AC voltage portion of the load 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 alternating magnetic flux in the stator windings. According to Faraday's law of electromagnetic induction, the alternating current flowing through the stator windings will induce current in the rotor bar (of the squirrel-cage rotor). This induced current in the rotor also produces alternating magnetic flux.
Even after setting the two alternating magnetic fluxes of the controller, the motor still cannot start. However, if the rotor is initially started by an external force in either direction, the motor will accelerate to its speed and maintain its rated speed. This behavior of single-phase motors can be explained by the dual-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 electric drills, hair dryers, etc. The various types of single-phase induction motors will be briefly discussed below. According to the starting mode, the basic types of single-phase asynchronous motors are: split-phase motors, capacitor start motors, permanent magnet capacitor running motors and other types.
The split-phase induction motor is one of the more widely used 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 that establishes a rotating magnetic field by providing two windings on the same stator core. The auxiliary winding or start winding has a series resistance, so its impedance essentially becomes a high resistance. Its winding method is different from the main winding, but compared with the main winding, it has fewer turns and a much smaller diameter.
Capacitor-started induction motors are similar to split-phase motors, but a capacitor is connected in series with the auxiliary winding. This is an improved version of a split-phase motor. Since the capacitor absorbs the leading current, the use of the capacitor increases the phase angle between the two currents (main current and auxiliary current), thereby increasing the starting torque. This is the main reason for using capacitors in single-phase induction motors.
Single-phase motor controller
The permanent magnet capacitor induction motor is also called a capacitor running motor, in which a low capacitor is connected in series with the start winding and is not removed from the circuit even in the running state. Due to this arrangement, no centrifugal switch is required. The capacitor can operate continuously. Low-value capacitors produce more leading phase shift, but the total starting current is less. Therefore, the starting torque produced by these motors will be much lower than the starting torque of capacitor-started motors.
The article mainly introduces the working principle of the single-phase motor controller. By browsing the full text, you can understand that the working principle of any voltage controller is based on the switching operation sequence of some power switches, that is, the thyristor. The way the thyristor is switched on allows the load to be connected to the AC power supply during a portion of each half cycle of the input voltage.
