Most of the applications of frequency converters (hereinafter referred to as -VFDs) are primarily due to the fact that VFDs can change the output frequency and thus change the speed of the motor. If the frequency of the VFD cannot be adjusted and no damage is found on the hardware, it can basically be considered that the maximum output torque of the VFD is less than the load progress torque caused by the failure, which is simply the VFD load can be poor.
1. The V/F ratio is too large:
Some of these VFDs are also called torque advancements. If this parameter is set too large, it may not be able to start properly. If the cuts are appropriate, the problem is solved.
Second, the acceleration time is too short:
Theoretically, the longer the acceleration time, the stronger the ability to progress the load. If the acceleration time is set too short, sometimes VFD overcurrent, overload, and overtemperature alarms will appear, but some will not appear, but will only be stuck in a certain frequency band.
3. Set the maximum frequency and the maximum frequency is too low:
Generally, these two parameters are set to the maximum value, but there are some careless electricians who change these two parameters, so it will also cause the frequency to be unable to upcycle.
Fourth, the vector control parameters do not match.
In the vector control mode, it is necessary to accurately measure the internal resistance, inductance and other parameters of the motor, and to match the vector parameters of the VFD. After a period of operation, the motor parameters will overheat and form deviations. At this time, the current will be too large to start the motor normally, and the frequency may be stuck at a certain point. Re-optimizing the parameters solves the problem.
5. In some special occasions, the VFD parameters are set incorrectly.
In some cases, the minimum frequency cannot be set too low. For example, in a constant pressure water supply system, after the minimum frequency is set to 0Hz, when the pump pressure is low, when the starting frequency of VFD and VFD is exceeded, the start is accelerated, and the pressure cannot be added. The frequency of the VFD cannot progress to 50Hz, which is about 38Hz. After adjusting the PID repeatedly, the frequency cannot be improved. Only by setting the minimum frequency of VFD at about 15-20HZ can we be satisfied with the acceleration of VFD and keep the pump at a certain pressure. Although the pressure satisfies the constant pressure requirements, the VFD cannot be completely stopped without water and always maintains the lowest frequency speed.
For example, the minimum frequency of VFD in the constant pressure water supply system cannot be set to 0HZ, generally at least about 20HZ, which is determined by the flow rate and head of the pump.
The workaround is to set the sleep frequency. When the frequency of the pump (e.g. 28HZ) is running for a few minutes, the pump will go to sleep. When the pressure drops to 0.2-0.4MP lower than the set pressure, the pump will start. Another way is to set up a punctual water supply, which is supplied in several time slots. In general, the constant pressure water supply manipulator has the above functions.
6. Hardware failure of VFD
A similar situation can occur when the transformer (Hall) of the VFD is unable to properly measure the correct current. This can also be the case when a measuring element on another motherboard is aging. These are also common encounters when modifying VFDs
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