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VFD Frequency is Difficult to Up-regulate Troubleshooting

If the hardware are not damaged, the reason for unable to raise the frequency is generally that maximum output torque of VFD is smaller than that of load lifting, namely the variable frequency drive is poor in driving loads.

Short acceleration time

In theory, the longer the acceleration time is, the stronger lifting capacity with load will be. If the acceleration time is set too short, some variable frequency drives display over-current or overload, overheat alarm, while some would not display, only the VFD stays in a specific frequency band.

Large V/F ratio

Some places are also called torque boosts. When this parameter is set too large, the VFD may be unable to start sometimes, a proper decrease would solve this problem.

Mismatch of vector control parameters

In the vector control mode, the internal resistance and inductance of the motor need to be precisely measured, and need to be well matched with the vector parameters of VFD. After a period of operation, motor become overheat, which would result in large current and make the motor unable to start normally, the frequency may also stay in a certain band, this problem can be solved by optimizing parameters.

Highest frequency and maximum frequency are set too low

Generally, these two parameters would be set to their maximum values. However, some careless electricians would also change these two parameters, thus making the frequency unable to raise.

Parameters need to be paired in some special occasions

In some occasions, the minimum frequency should not be set too low. For example, in the constant pressure water supply system, if the minimum frequency is set to be 0Hz, the VFD accelerates as the frequency exceeds the starting frequency of VFD under a low pump pressure, the pressure can’t be boosted and the VFD frequency can’t be increased to 50Hz. It keeps at 38Hz and can’t be increased even for repeated setting and adjusting PID. However, when the minimum frequency is set to be about 15-20Hz, the VFD acceleration can meet and water pump can be kept at a constant pressure. However, when stopping water supply, VFD can’t stop working but should maintain the speed of minimum frequency.

That’s because: the minimum VFD frequency in the constant pressure water supply system can’t be 0Hz, but should be 20Hz at least, which is jointly determined by the flow and head of the pump.

The solution is to set a dormancy frequency. When the pump stops working, it works at a specific frequency (such as 28Hz) for several minutes and then goes to sleep. When the pressure decreases to 0.2-0.4M lower than the setting pressure, the pump starts. Another solution is to set regular water supply, water will be supplied in several periods. Generally, a constant pressure water supply controller covers all of above functions.

Hardware faults

When the transformer (Hall) of VFD goes wrong, it can not measure the correct current normally, similar conditions would also appear. In addition, aging of a certain measurement component on the main board would also lead to such a condition. These are commonly seen in the maintenance of variable frequency drive.

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