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A single-phase bi-directional neutral point clamped AC/DC converter with the functions of being a power factor corrector and an active filter is proposed, to reduce current harmonics and compensate for the reactive power current drawn from a nonlinear load. Based on neutral point clamped topology, the voltage stress of the power device is clamped to half the DC bus voltage instead of the full DC link voltage in a conventional half and full bridge pulse-width modulation (PWM) AC/DC converter. The line current tracking, DC fink voltage regulation and neutral point voltage compensation are performed by an inner loop current controller, an outer loop voltage controller and a voltage balance compensator, respectively. To generate a three-level PWM pattern on the AC terminal of the AC/DC converter, a region detector of the mains voltage is employed. Based on the proposed control scheme, the converter can draw a clean sinusoidal fine current with unity input power factor and achieve DC bus voltage regulation. The effectiveness of the proposed AC/DC converter with the function of power factor corrector as well as active filter is confirmed by the experimental results.
Date of Publication: Jan. 2002