Frequency Domain Closed-Loop Analysis and Sliding Mode Control of a Nonminimum Phase Buck-Boost Converter

In this paper, a robust closed-loop cascaded controller is designed and rigidly analyzed for an inverting buck-boost converter. The fast inner current loop uses sliding mode control (SMC). The slow outer voltage loop uses the proportional-integral (PI) control. Analysis of stability and robustness, proof of nonminimum phase structure, and proper selection of PI gains are based on the closed-loop transfer function. The controller design is facilitated by the system frequency responses. The output voltage transients are predictable during step changes of the input voltage and load resistance. The operating range of the reference voltage is discussed. The simulation results show that the reference output voltage is well tracked under modeling uncertainties, disturbances or step changes of parameters, confirming the validity of the proposed method.