The principle of single-phase asynchronous motor
An asynchronous motor that uses a single-phase AC power supply is called a single-phase asynchronous motor. Single-phase asynchronous motors are convenient to use and widely applied because they only require single-phase alternating current. They also have the advantages of simple structure, low cost, low noise, and minimal interference with radio systems. Therefore, they are commonly used in household appliances and small power machinery with relatively low power. Such as electric fans, washing machines, refrigerators, air conditioners, range hoods, electric drills, medical devices, small fans and household water pumps, etc. Since the single-phase voltage in China is 220V, while in foreign countries such as 120V in the United States, 100V in Japan, and 230V in Germany, the United Kingdom, and France, when using single-phase asynchronous motors from abroad, it is necessary to pay attention to whether the rated voltage of the motor is the same as the power supply voltage.
A single-phase asynchronous motor is composed of a stator, rotor, bearings, casing, end cover, etc. Single-phase asynchronous motors are often made into small motor devices. Their motor capacity is very small and they only need to be powered by a single-phase AC power supply. As driving motors, the power of a single-phase asynchronous motor is only a few watts, tens of watts or hundreds of watts.
A single-phase asynchronous motor is a rotating motor powered by a single-phase AC power supply, and its stator winding is single-phase. When single-phase alternating current is connected, an alternating pulsating magnetic field will be generated in the air gap between the stator and rotor, so a single-phase asynchronous motor cannot start by itself. [2] In an AC motor, when an alternating current passes through the stator winding, an armature magnetomotive force is established, which has a significant impact on the motor's energy conversion and operational performance. Therefore, when single-phase AC is fed into a single-phase AC winding, a pulsating magnetic motive force is generated. This magnetic motive force can be decomposed into two rotating magnetic motive forces of equal amplitude and opposite rotational speed, thereby establishing a forward and reverse magnetic field sum in the air gap. These two rotating magnetic fields cut the rotor conductors and respectively generate induced electromotive force and induced current in the rotor conductors. The working principle of a single-phase asynchronous motor [3] : This current interacts with the magnetic field to generate positive and negative electromagnetic torques. The forward electromagnetic torque attempts to make the rotor rotate forward; Reverse electromagnetic torque attempts to reverse the rotor. The sum of these two torques is the combined torque that drives the motor to rotate.
Whether it is the forward or reverse magnetic field, the relationship between their magnitudes and the slip rate is the same as that of a three-phase asynchronous motor. If the rotational speed of the motor is n, then for the forward magnetic field, the slip is: s+=(n1-n)/n1= S. For the reverse magnetic field, the slip is: s-= (-n1-n)/-n1= S. From the T-s curve graph of the single-phase asynchronous motor, it can be known that the main characteristics of the single-phase asynchronous motor are: When n=0,s=1,T=T++ T- =0, it indicates that the single-phase asynchronous motor has no starting torque. If no other measures are taken, the motor cannot start. (2) When s≠1, T≠0. T has no fixed direction and it depends on whether s is positive or negative. (3) Due to the existence of reverse torque, the combined torque also decreases accordingly, so the overload capacity of single-phase asynchronous motors is relatively low.
The working principle of capacitive phase-separated starting
When starting up, switch K closes, causing the phase difference between the currents I1 and I2 of the two windings to be approximately 90°, thereby generating a rotating magnetic field and the motor starts to rotate. Rotate forward
Often, the centrifugal switch is flung off and the starting winding is cut off.
The working principle of shaded-pole single-phase motors
After current is passed through the stator, part of the magnetic flux passes through the short-circuit ring and an induced current is generated in it. The current in the short-circuit loop hinders the change of magnetic flux, causing a phase difference in the magnetic flux generated between the part with the short-circuit loop and the part without it, thereby forming a rotating magnetic field and making the rotor rotate.
The rotation direction of the motor in the T-s curve graph of a single-phase asynchronous motor: instantaneous needle rotation. Because the magnetic flux of the part without a short-circuit loop is ahead of that of the part with a short-circuit loop.
