A Single-stage, Single-phase, Ac-dc Buck-boost Converter for Low-voltage Applications

─The suitability of a single-stage ac-dc buck-boost converter for low-voltage applications is investigated. Indepth discussion and analysis of the converter’s operating principle, basic relationships that govern converter steadystate operation, and details of the necessary control structures needed to comply with the grid code are provided. The validity of the proposed system is confirmed using PSCAD/EMTDC simulations, and is substantiated experimentally. The buck-boost converter under investigation has good dynamic performance in both buck and boosts modes, and ensures near unity input power factor over the full operating range, whilst having fewer devices and passive elements than other published versions of the buck-boost converter. Index Terms ─ ac-dc converter, unity power factor, buck-boost converter. List of Symbols δ duty cycle Ldc dc side inductance (H)  supply angular frequency (rad/s) Ls ac side inductance (H) Cdc dc side capacitance (F) Rdc load resistance (Ω) Cs ac side capacitance (F) Rs ac side resistance (Ω) D1 D4 bridge rectifier diodes S power electronic switch Dbd blocking diode ton dwell time of the switch within each switching cycle (s) c I average dc capacitor current (A) toff off time of the switch within each switching cycle (s) dc I average load current (A) Ts switching period (s) i I average current entering the dc link node: equal to the instantaneous dc inductor current IL during Modes 2 and 4 only (A) vcm vcs peak ac source capacitor voltage (V) ac source capacitor voltage (V) IL instantaneous dc side inductor current (A) Vdc instantaneous dc output voltage (V) L I average inductor current (A) dc V average dc output voltage (V) im peak fundamental supply current (A) L V average dc inductor voltage (V) is input supply current (A) Vm peak supply phase voltage (V) is * input current control reference (A) vs supply voltage (V)