1. How is back electromotive force generated?
Back electromotive force is also called induced electromotive force. Principle: the conductor cuts the magnetic lines of force.
The rotor of the permanent magnet synchronous motor is a permanent magnet, and the stator is wound with coils. When the rotor rotates, the magnetic field generated by the permanent magnet is cut by the coils on the stator, generating a back electromotive force on the coil (in the opposite direction to the terminal voltage U).
2. Relationship between back electromotive force and terminal voltage
3. The physical meaning of back electromotive force
Back EMF: generates useful energy and is inversely correlated with heat loss (reflects the conversion ability of the electrical appliance).
4. The size of back electromotive force
Summarize:
(1) The back EMF is equal to the rate of change of magnetic flux. The higher the speed, the greater the rate of change and the greater the back EMF.
(2) The flux itself is equal to the number of turns multiplied by the flux per turn. Therefore, the higher the number of turns, the greater the flux and the greater the back EMF.
(3) The number of turns is related to the winding scheme, star-delta connection, number of turns per slot, number of phases, number of teeth, number of parallel branches, and full-pitch or short-pitch scheme;
(4) The single-turn flux is equal to the magnetomotive force divided by the magnetic resistance. Therefore, the larger the magnetomotive force, the smaller the magnetic resistance in the direction of the flux and the larger the back electromotive force.
(5) Magnetic resistance is related to the air gap and the pole-slot coordination. The larger the air gap, the greater the magnetic resistance and the smaller the back electromotive force. The pole-slot coordination is relatively complex and requires specific analysis;
(6) The magnetomotive force is related to the residual magnetism of the magnet and the effective area of the magnet. The larger the residual magnetism, the higher the back electromotive force. The effective area is related to the magnetization direction, size and placement of the magnet, which requires specific analysis;
(7) Remanence is also related to temperature. The higher the temperature, the smaller the back EMF.
In summary, the factors affecting back EMF include rotation speed, number of turns per slot, number of phases, number of parallel branches, full pitch and short pitch, motor magnetic circuit, air gap length, pole-slot matching, magnetic steel remanence, magnetic steel placement and size, magnetic steel magnetization direction, and temperature.
Post time: Sep-18-2024