Fundamental Harmonic‐Based Equivalent Modeling and Stability Effect of <i>LC</i> Filter Feedforward Ripple in Cascaded Converter

ABSTRACT In a cascaded converter, an LC filter is usually added to the front of load converter to attenuate the current ripple fed forward to the source converter. When the parameters of LC filter are improperly selected, feedforward current ripple (FCR) can induce fast‐scale instability in the source converter. However, the circuit order introduced by load converter and its LC input filter increases the modeling complexity of the cascaded converter. To simplify the modeling complexity, a fundamental harmonic‐based equivalent modeling method is proposed for the LC input filter FCR. A peak‐current‐mode controlled buck converter cascaded with an open‐loop buck converter with an LC input filter is considered. An equivalent model of the cascaded converter is established, and the monodromy matrix is then obtained by using the Filippov's method and the Floquet theory. Subsequently, the eigenvalue analyses are carried out, and the stability boundaries in the chosen parameter planes are obtained. Further, the generality of the proposed method is demonstrated by another case. The results indicated that with the proposed method, the stability effects of the LC input filter FCR can be effectively predicted. Increasing the inductance or capacitance of the LC input filter and decreasing the phase difference between the source and load converters can cause fast‐scale instability in source converter. Finally, the experimental results are used to verify the correctness of the theoretical and simulation results.