Must have good inverter knowledge(3)

23. Short-time overload, quick start and quick stop under heavy load, there is a clutch, when the inverter and the clutch just contact, the slip will become larger and the current will increase, and the inverter will be controlled by frequent jogging.

24. When the motor runs at about 40HZ, can the inverter be selected to be small? For constant power load, when the speed drops, the power does not decrease, so the inverter power cannot be selected to be small. For constant torque load, when the speed decreases, the torque does not decrease, and the current does not decrease. For quadratic law load, the frequency conversion capacity can be appropriately reduced, but according to the above, it is necessary to know the maximum operating current, The size of the torque, and whether to respond quickly.

25. The use of submersible pumps needs to increase the capacity of frequency conversion, because there will be debris in underwater operation, and there will be an inrush current at this time. Another solution is to add an output reactor, which can suppress the instantaneous current impact.

26. When the inverter drives multiple motors, it is required to be 1.05 to 1.1 times the sum of the motor currents.

27. Damage of equalizing resistor: The main reason is that there is a problem with the electrolytic capacitor. When the electrolytic capacitor has a problem, the capacity becomes smaller, c=q/u, the voltage becomes larger, and the voltage across the equalizing resistor becomes larger. If the margin is not large, it will burn out the resistor.

28. IGBT, why is there an anti-parallel freewheeling diode? The motor is an inductive load, and the current lags behind the voltage. At this time, there will be two types of electromagnetic work to generate back electromotive force and electromotive force to overcome the magnetic field work. If there is no freewheeling diode, the work of the circuit will be Distortion occurs.

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