This paper presents the implementation of feedforward in digital domain to meet the audio susceptibility as per MIL STD 461C for voltage mode digitally controlled DC-DC converters. The feed-forward is accomplished through the estimation of duty ratio based on the input voltage at every switching cycle. The prototype converter developed is having galvanic isolation in the forward and feedback path and is based on single ended forward topology. An optimised discrete controller is provided in the feedback path to achieve desired dynamic performance. The feed forward scheme was implemented along with discrete feedback controller using a 16-bit fixed point microcontroller. The design of optimised discrete compensator and the audio rejection of a converter with such a feedback controller are presented. The simulation model of the converter with proposed digital feed forward/feedback controller using SIMULINK and its results against input disturbances are also presented. Experimental results are presented in this paper to validate the theoretical analysis.
Keywords: DC-DC converter, digital control, digital feedforward, PID controller, audio susceptibility, duty ratio estimator