What Do Constant Power And Constant Torque Mean in Variable Frequency Speed Regulation?

Generally speaking, the rated speed value obtained by the factory motor is based on the given power frequency voltage (380V, 50 Hz). If 380V is not reached under actual working conditions, such as only 300V, 50 Hz, it is obviously undervoltage. Basically, it cannot reach the rated speed value, because according to the design of the motor, there must be a voltage of 380V and a frequency of 50 Hz. To excite, under the rated voltage, the magnetic field strength cannot be reached, and the magnetic flux is very small, so it will definitely affect the speed, not because of the 60f/p formula to see the change in speed. For example, under the input of 380V 40Hz, according to the formula E=K*F*Q, E remains unchanged, F decreases, then Q magnetic flux becomes larger, which is an overvoltage situation, too much excitation, magnetic flux for a long time, will cause the motor to heat up and may burn. Therefore, the value of the magnetic flux should not be too large, which is determined by the load-bearing capacity of the motor when it is designed. Usually in constant torque speed regulation (less than 50 Hz), the magnetic flux at this time is the rated magnetic flux, also known as full magnetic flux. If the voltage/frequency becomes larger, it will exceed the flux value, causing the motor to heat up.

Constant torque speed regulation:

That is, keep the flux constant, v/f=q (flux) is a constant value. Why is it called constant torque speed regulation? That is, the load torque is a fixed value, and the motor output torque is also a fixed value. See the formula: t=k*i*q, at this time q is a constant, then the motor output torque is proportional to i, because the value of q can be calculated by the nameplate V (rated power supply voltage)/50 Hz, so when q is a constant, the rated current of the coil (regardless of whether there is a load, by determining the maximum through-current, the maximum torque output of the motor can also be determined (it can also be determined how much torque the motor can drive a constant load), so the overcurrent capacity of the motor reflects the overload (torque) capacity of the motor.

To provide a constant torque speed, it only needs to be delivered by the inverter through a motor modulated by a certain frequency (flux, predetermined value ratio), the load torque is also a fixed value, then the constant N , T of course, the input power P is therefore fixed. If F increases, the speed N increases, the power P will become larger, because the torque T will not become larger due to the increase in speed (this is also called constant torque load, such as conveyor belt. The constant torque characteristic is independent of load torque and speed, and the torque at any speed remains constant or basically constant in total applications, such as conveyor belts, mixers, or extruder type friction loads and cranes, hanging potential energy loads, etc.)

Another point is that the rated speed is the value obtained when the motor is idling. As for the meaning of this value, when the rated voltage and rated power are reached, the larger the value, the smaller the output torque. This is a feature of constant power speed regulation. Formula T=9550*P/N(rated speed). Therefore, in the case of F type 50Hz (when the output power is the largest), when n is large, attention should be paid to the fact that T is small to avoid accidents caused by T being too small and less than the load torque. In constant power speed regulation, speed regulation is achieved by reducing the magnetic flux to reduce the output torque and thus increase the speed, so this is also called weak magnetic speed regulation.