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Vsd Output


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We all agree in conventional VSD that by applying rated voltage at nominal frequency F at the input of a VSD, the VSD is capable of delivering a varaiable output up to the rated voltage at the nominal frequency F. For instance at 400 V 50 Hz frequency on the input side, the VSD will give a variable output until it achieves 400 V at 50 Hz. It is also understood that the VSD might increase the frequency well above 50 Hz but with no increase in output torque.

My question is simple, I wish to have an output of 500 V @ 50 Hz with a 400 V 50 Hz supply taking in consideration that the input supply is first rectified to round 590 V. My intention is to used a 400 V 50 Hz supply to power a 500 V 50 Hz electric motor.





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Increase in DC voltage is due to rectification from AC, which will again decrease after inversion. For your basic requirement to run a 500V motor on a 400V input supply, I think you can do it if you are going to run the motor at around 40 Hz or less. If you go beyond, the drive should trip on overcurrent fault. Im not sure what is your operating speed range, so cant add further.




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Hi Bob


The maximum output voltage from an inverter is a little less than the input voltage, so if you wish to increase the voltage, you will need to add a transformer to either the input, or the output of the drive.

With some drives, a transformer on the output would prevent the drive from performing correctly due to the mathematical modeling of the motor which would now be out of specs. Simple V/Hz drives would not be a problem.


A step up transformer on the input would require a higher voltage drive. A step up transformer on the output would probably require an open loop drive.


You could run a standard drive on 400 V and set the drive up as though it was 500V. This would cause the voltage at frequencies well below 50Hz, to be the same as they would if the supply was 500V, so you would get full torque output, but the drive would then begin voltage limiting at 40Hz and the output torque would be reduced. It depends on the type of load and thee torque requirements.


Best regards,

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