Measurement of the Loop Gain Frequency Response of Digitally Controlled Power Converters

The study of the loop gain frequency response in a power converter is a powerful tool commonly used for the design of the controllers used in the control stage. As the control of medium- and high-power electronic converters is usually performed digitally, it is useful to find a method to measure the digital loop gains. The purpose of this paper is to present a method for properly measuring the loop gain frequency response of digitally controlled power converters by means of an analog frequency response analyzer (FRA). An analog sinusoidal reference signal generated by the FRA is injected through an analog-to-digital converter into the digital controller, and added to the discrete feedback signal. To obtain the frequency response of the open-loop gain, both feedback and disturbed feedback signals are sent back to the FRA by using the pulsewidth modulation peripherals of the controller.