1. During weak magnetic speed regulation, the physical quantity inside the motor changes as follows: the armature voltage decreases because the armature electromotive force decreases at this time; At this point, if the load remains constant, the current will increase. Because it is necessary to maintain the load torque unchanged.

2. For constant excitation DC motor speed regulation, the higher the armature voltage, the higher the motor speed. It is a proportional relationship. For constant torque speed regulation, no further increase is allowed after the armature voltage reaches the rated value. At this point, if you want to increase the speed again, you need to weaken the magnetic field. At this time, it is a constant power speed regulation. Namely, power=speed X torque. As the speed increases, the torque decreases.

The relationship between torque, current, and magnetic flux (excitation): Motor torque=armature current X magnetic flux. If the magnetic field is weak and the armature voltage is rated, the speed will increase. If the armature current does not change at this time, the torque will decrease. If the torque is to be maintained constant, the armature current needs to increase under weak magnetic field conditions.

3. For separately excited motors, during weak excitation, as the load is determined, the excitation current decreases, the armature current increases, the speed increases, the armature voltage remains unchanged, and the torque remains unchanged.