Frequency response measurement of DC-DC converters using a lock-in algorithm

This paper presents a method to measure the control-to-output transfer function of dc-dc converters in open-loop. A sinusoidal perturbation is injected to the nominal value of the duty cycle, and a dual-phase lock-in algorithm is off-line applied to process the digitized input and response signals in order to compute the gain and phase of the transfer function. Lock-in algorithm is used because it provides a high signal-to-noise ratio (SNR). This method is applied to a buck converter. The accuracy of the method is evaluated, and it is compared to the Discrete Fourier Transform (DFT) in simulation. Finally, the simulations are experimentally verified. The proposed method is off-line implemented, but it can also be implemented in real time into a digital controller.