Three-Phase Two-Phase-Clamped Boost-Buck Unity Power Factor Rectifier Employing Novel Variable DC Link Voltage Input Current Control

Battery chargers supplied from the three-phase mains are typically realized as two-stage systems consisting of a three-phase PFC boost-type rectifier with an output DC link capacitor followed by a DC/DC buck converter if boost and buck functionality is required. In this paper, a new modulation scheme for this topology is presented, where always only one out of three rectifier half-bridges is pulse width modulated, while the remaining two phases are clamped and therefore a higher efficiency is achieved. This modulation concept with a minimum number of active half-bridges, denoted as 1/3 rectifier, becomes possible if in contrast to other modulation schemes the intermediate DC link voltage is varied in a six-pulse voltage fashion, while still sinusoidal grid currents in phase with their corresponding phase voltages and a constant battery output voltage are obtained. In this paper, a detailed description of the novel 1/3 rectifier's operating principle and the corresponding control structure are presented and the proper closed loop operation is verified by means of a circuit simulation. Finally, the performance gain of the 1/3 rectifier control scheme compared to conventional modulation schemes is evaluated by means of a virtual prototype system.