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In this paper, the nonlinear model of the bridgeless single-switch ac-dc  single-ended primary-inductor converter (SEPIC) in discontinuous conduction mode is derived. In addition, a robust control method is introduced to accommodate the variations in input voltage and load current. The current-mode controlled power converter is designed to operate in buck and boost modes. The proposed closed-loop SEPIC converter is simulated in MATLAB to validate the design approach. The current-mode control scheme is also compared with the conventional voltage-mode controller. It is confirmed that the proposed control scheme exhibits precise tracking performance and enhanced transient response under large disturbances.

The pulse-with modulated (PWM) dc-dc buck-boost converter is a non-minimum phase system, which requires a proper control scheme to improve the transient response and provide constant output voltage during line and load variations. The pole placement technique has been proposed in the literature to control this type of power converter and achieve the desired response. However, the systematic design procedure of such control law using a low-cost electronic circuit has not been discussed. In this paper, the pole placement via state-feedback with an integral control scheme of inverting the PWM dc-dc buck-boost converter is introduced. The control law is developed based on the linearized power converter model in continuous conduction mode. A detailed design procedure is given to represent the control equation using a simple electronic circuit that is suitable for low-cost commercial applications. The mathematical model of the closed-loop power converter circuit is built and simulated using SIMULINK and Simscape Electrical in MATLAB. The closed-loop dc-dc buck-boost converter is tested under various operating conditions. It is confirmed that the proposed control scheme improves the power converter dynamics, tracks the reference signal, and maintains regulated output voltage during abrupt changes in input voltage and load current. The simulation results show that the line variation of 5 V and load variation of 2 A around the nominal operating point are rejected with a maximum percentage overshoot of 3.5% and a settling time of 5.5 ms.

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