How to measure ripple factor automatically for a pulsating dc output(0-300 v)?
You need to define what you want to measure better if the answer is to be sure of meeting your need.
You may define ripple factor as eg
eg if the supply is 300V max and 270V at the bottom of the ripple then
How to do this acceptably depend on acceptable accuracy and what is meant by automatic.
(1) Automatic, easy, minor technology.
Micro controller with ADC.
(2) Minimum effort.
"Automatic determination of Voltages".
eg Vmax can be determined by using a peak detector and an RC filter + a diode. - Vin is passed via a diode and resistor to a capacitor. A much larger resistor is connected from capacitor to ground. (eg diode via 1k to 100 uF. 1M to ground).
Vmin can be determined using a minimum voltage detector.
Capacitor voltage will be Vmin +Vdiode.
This give Vmax and Vmin which can be measured on analog meters or whatever and scaled as required.