Stability Effect of Load Converter on Source Converter in a Cascaded Buck Converter

In a cascaded power converter, the input current ripple of load converter is fed forward to the output capacitor of source converter and results in reshaping the output capacitor current and output voltage ripples of source converter. To investigate the stability effect of feedforward current ripple of load converter on source converter, a cascaded power converter comprising two peak-voltage-ripple controlled buck converters is taken as an example. First, the stability effects of chosen circuit parameters of the source converter in cascaded operation and standalone operation are demonstrated and compared. Second, by describing three switching state sequences induced by the feedforward current ripple, a discrete-time map model is established for the cascaded power converter. Based on the map model, the instability mechanism of source converter with the variations of the circuit parameters is thereby expounded, and the stability boundaries are obtained in the circuit parameter planes. The results show that the stability effects of the circuit parameters of source converter with feedforward current ripple are essentially different from those in the standalone operation. The theoretical analyses are verified by the simulation results and experimental results.