Unified Closed-Loop Control and Parameters Design of Buck-Boost Current-Fed Isolated DC-DC Converter With Constant Power Load

The bidirectional buck-boost current-fed isolated dc-dc converter suffers from the instability when feeding the constant power load (CPL). The mathematical models of buck and boost subsystems of the converter with CPL are derived. It is proven that CPL leads to the instability of the both subsystems and the system cannot be stabilized by the single output voltage closed-loop control. The active damping method is introduced to ensure the closed-loop stability of the converter. An optimal design method of the active damping feedforward coefficient is proposed to keep the open-loop stability of the two subsystems and ensure a good dynamic response. An input voltage feedforward is used to overcome the influence of nonminimum-phase characteristics between dynamic response and the stability of the boost mode. The unified design method of the closed-loop controller parameters based on Hurwitz criterion and frequency response is proposed to keep the closed-loop stability of the two subsystems. The correctness and feasibility of the parameter design method are verified by detailed experimental results.