1 and weak magnetic speed regulation are all speed regulation processes above the base speed, that is, the back electromotive force reaches the rated value at this time. According to Equation 2, at this time, both E and Ce are unchanged. If n is going to rise, only φ will fall, thus realizing weak magnetic acceleration. It is not that the back electromotive force decreases, but the resistance decreases.
2. If there is no magnetic field, according to Formula 3, there will be no electromagnetic torque. Under the action of the resistance moment, even if only the friction resistance of the motor itself remains, the motor will gradually stop rotating. But the actual situation is that even if there is no excitation current, there will be electromagnetic torque output due to the residual magnetism of the motor itself. When it is greater than the current resistance moment (light load or load loss), the rotating speed will gradually increase and get out of control, resulting in out of control.
3. Because Ia can't be greater than Ie when the motor runs continuously, otherwise the motor will be overloaded and burned out. According to Formula 3, if Ia wants to continue the weak magnetic acceleration after reaching Ie, the output torque will inevitably decrease, that is, the higher the speed, the more boring the motor will be. This may be what the questioner said about the smaller ampere force, rather than the smaller resistance of the weak magnetic field to the rotor. According to equation 2 and 1, u is constant at this time. Because P=U*I, the weak magnetic speed regulation area above the base speed is also called constant power area.
4. Theoretically, AC motor and DC motor have similar speed regulation principles, similar core mathematical models and different control methods. In the calculation formula, only a power factor angle and phase/line transformation are added. Therefore, weak magnetic acceleration is also used in AC motor speed regulation, but it is not called this name. It is generally called base speed and maximum speed, or rated frequency and maximum frequency.