how the frequency is increased and decreased in a VFD ?

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I want to ask you that how the frequency is increased and decreased in a VFD ?

as far as i know there are bridge rectifier which converts the AC supply into dc and then there is DC Bus link which not only store the dc bus voltage but also deliver the power to the inverter section which contains few IGBTs (on and off thousand times per second) and they use PWM method for the output.

I want to know that how an IGBT works inside a VFD ? what are the input and output of an IGBT inside a VFD ?

what process takes place that enable vfd to generate particular output to a particular input ? when frequency reference command is low it generates low output and when frequency reference command is higher it generates high output

thanks
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I'm under the impression that there's a fairly understandable explanation at Wikipedia https://en.wikipedia.org/wiki/Variable-frequency_drive

In a short, the motor frequency is generated by a digital three-phase sine generator, multiplied with a frequency variable voltage setpoint and converted to control signals for the output stage (IGBT or MOSFET) by a pwm modulator.

what are the controlling of VFDs ? How they be controlled ?

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what input is applied to the IGBT(s) and which component is generally used to give out the input(s) to the IGBT(s) ?