# VFD Inverter power compensation

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#### Ravindra

We are expanding our factory capacity. As said above the 37 KW motor is taking load 50 amps at 37.5 Hz. As we decide to operate the same 43 hz during the factoy expansion. Could you please suggest me , as per ohms law

power = voltage x current x power factor.

in the inverters the power factor will increse or decrease. The inlet power factor is .75

Here in this case, when we expanded, and we decide to run at 43 HZ, the approximate voltage at the motor terminals 340 V ac. I am not sure. in this situation if the motor load increses can we increse the motor voltage by using the Voltage boost method to compensate the amps signal or not.

i mean rather than increasing the current, by injecting more voltage can we reduce the amps or not.

please clarify. Without changing the motor and VFD we want to do the expansion.

regards,
mullapudir
[email protected]

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#### Hakan Ozevin

Dear Mullapudir,
You cannot control the current of the motor by changing voltage, because motor draws a current
If you increase the frequency, power may increase or decrease. It depends on the torque
characteristics of the load. For a constant torque load power will increase linearly (current
will be the same), for a fan it will increase more than linear and for reverse torque load (e.g.
mixer) it will decrease (current will decrease as well).
The cos phi for a DC-link voltage source drive is nearly 1, but since it draws harmonic currents,
the power factor is less than 1 (0.8 to 0.5 depending on the number of pulses). You have to look at the power factor curves of your drive, but I dont think it will change too much in your case.

Therefore, you have to first decide what kind of torque-speed characteristics your load has.

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#### Tom Gianni

I'll comment on a few of your questions.

Voltage boost feature: This is to compensate for the non-linear (and excessive) voltage drop percentage (due to IR) at low output Volts which
occurs at low Hz in V/Hz control. Vboost adjustment only affects the V/Hz curve at low freq range.

If it is a constant torque load the current draw should be about the same as the load and V/Hz ratio about the same. Does the 15% higher Hz cause a higher current due to a power factor decrease? This, I'm not sure off the top of my head. Haven't worked with VFDs for 3 plus years so all my files aren't handy.