Stability Analysis of Cascaded Converter via Equivalent Modeling of Feedforward Ripple

In a cascaded converter, the input current ripple of the load converter is fed forward to the source converter. This feedforward current ripple from load converter has a significant stability effect on the source converter. However, the additional orders and multiple switching-state sequences introduced by the load converter greatly increase the complexity of investigating the stability effects of feedforward current ripple. To address this issue, an equivalent modeling method of the feedforward current ripple is proposed. According to the method, the feedforward current ripple is modeled as the main components of its Fourier series. Based on the equivalent representation, the bifurcation analysis of the source converter is carried out. Then, a discrete-time map model of the source converter is established and its stability is investigated. Furthermore, the deviations between the stability predictions based on the equivalent representation and those based on the feedforward current ripple are evaluated. The results indicate that the stability prediction accuracy using the equivalent representation is related to the duty-cycle of the source converter. The correctness of the theoretical analyses is verified by the simulation and experimental results.