Frequency inverters

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A frequency inverter controls AC motor speed. The frequency inverter converts the fixed supply frequency (60 Hz) to a variable-frequency, variable-voltage output to enable precise motor speed control. Many frequency inverters even have the potential to return energy to the power grid through their regenerative capability.
energy consumed
The high frequency edges of switched waveforms can cause capacitively coupled currents to flow from windings to frame, returning through the bearings, and these can accelerate corrosion in the bearings, causing early failure. Small filters on the motor leads allowing these currents to return locally to ground will avoid this.
In inverter regular inspection, we must cut off power before operation. Wait 4minutes (the bigger the longer, the maximum waiting time is 15 minutes) till the frequency inverter display panel LED indicator lights turn off, to make the main circuit DC filter capacitor fully discharged, and measure with a multimeter to confirm before proceeding.
Our one frequency inverter which drives 0.37 KW 400 V dosing pump motor intermittently (once in a month or once in two months) shows DC link fault and the speed is reduced to zero.
Is it because of rewinding of the motor; winding geometry might have changed that affects the frequency inverter? If this is the problem then why this fault is not coming whenever it is in service? (It waits for 1month or two months some time the fault comes in a weak also)
Quality frequency inverters incorporate either an AC Reactor or DC Reactor (choke). Their inclusion in the basic design of the frequency inverter allows the design engineer to maximize the advantages of the choke. Their function is to reduce the current distortion caused by the input stage rectifiers by slowing the rate of change of current, and thus charging the internal capacitor at a slower rate over a longer time.
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