A time-length compensation algorithm for sub-harmonic oscillation elimination in digital controlled primary-side regulation flyback converter

A time-length compensation algorithm to eliminate sub-harmonic oscillation is proposed in primary-side regulation flyback converter with average current control method to realize constant output current. A matrix analysis method is put forward to analyze the sub-harmonic oscillation in CCM mode. Based on the above analysis, a simple time-length compensation algorithm is added to eliminate sub-harmonic oscillation. The switch on-time of the previous switching cycle is applied for the compensation algorithm to calculate the average current of the next switching cycle. Compared to traditional compensation algorithm, the cost is low as no ADC or fast DAC are needed and the time-length compensation algorithm is very simple. A 64W prototype is applied to verify the above analysis. Experiments prove that the matrix analysis method is feasible and the time-length compensation algorithm is effective to eliminate sub-harmonic oscillation. It can be used to eliminate sub-harmonic oscillation in other power supplies.