Principle analysis of single-phase motor

When a single-phase sinusoidal current passes through the stator winding, the motor generates an alternating magnetic field. The strength and direction of the magnetic field change sinusoidally with time, but it is fixed in spatial orientation, so the magnetic field is also called alternating. Pulsating magnetic field. The alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with opposite rotation speeds at the same rotation speed. When the rotor is stationary, the two rotating magnetic fields generate two equal and opposite torques in the rotor, so that the synthesis The torque is zero, so the motor cannot rotate. When we use an external force to rotate the motor in a certain direction (such as clockwise rotation), the movement of the cutting magnetic field between the rotating magnetic field of the rotor and the clockwise rotation direction becomes smaller; between the rotating magnetic field of the rotor and the counterclockwise rotation direction The cutting magnetic line motion becomes larger. This balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate in the direction of the push.

In order to make the single-phase motor rotate automatically, we can add a starting winding to the stator. The starting winding is 90 degrees out of phase with the main winding. The starting winding must be connected in series with a suitable capacitor so that the current with the main winding is The phase is approximately 90 degrees out of phase, the so-called phase separation principle. The two currents that differ by 90 degrees in time are passed into two windings that are 90 degrees apart in space, which will produce a (two-phase) rotating magnetic field in space. The capacitive phase-separated motor wiring diagram and vector diagram are in this rotating magnetic field. Under the action, the rotor can be started automatically. After starting, when the speed rises to a certain value, the starting winding is disconnected by means of a centrifugal switch or other automatic control device installed on the rotor. Only the main winding works during normal operation. Therefore, the starting winding can be made in a short-time mode of operation. But there are many times when the starting winding is not broken. We call this kind of motor a single-phase motor. To change the steering of this motor, just change the terminal of the auxiliary winding.

In a single-phase motor, another method of generating a rotating magnetic field is called a shaded pole method, also known as a single-phase shaded pole motor. The stator of the motor is made of a salient pole type, and has two poles and four poles. Each pole has a small slot at the 1/3--1/4 all-pole surface, the magnetic pole is divided into two parts, and a short-circuited copper ring is placed on the small part, as if the magnetic poles are covered. So called the cover pole motor. The single-phase winding is set on the entire magnetic pole, and the coils of each pole are connected in series, and the polarity generated by the poles must be arranged in order of N, S, N, and S. When the stator winding is energized, a main magnetic flux is generated in the magnetic pole. According to Lenz's law, the main magnetic flux passing through the short-circuited copper ring generates an induced current that is delayed by 90 degrees in phase in the copper ring, and the magnetic current generated by the current is generated. The pass also lags the main flux in phase, and its function is equivalent to the start winding of the capacitive motor, thereby generating a rotating magnetic field to rotate the motor.