hello,

not wasting the time,

Iam designing a power factor correction circuit. (Not yet put on the PCB)
Just paper work is going on.

the phase angle between the voltage and current are measured in terms of a voltage.
this voltage is compared with a preset (0 volts) to achieve 0 time difference (unity pf).

my question is, how can i design a variable capacitance controlled by a voltage.

any idea please...
thankyou

 

How much capacitance do you need?

 

Power factor correctors typically switch banks of capacitors in & out of circuit using large contactor-style relays.

One setup uses multiple banks of capacitors, with each bank double the value of the last.

If you imagine a setup with eg. six banks, values 1, 2, 4, 8, 16, 32 KVAR, it's possible to set any value from 0 to 63 KVAR by controlling the contactors with the equivalent six bit binary value.

Use a binary counter and step the value up or down depending if the capacitance needs to increase or decrease.