Active DC Link Capacitance Reduction in Grid-Connected Power Conversion Systems by Direct Voltage Regulation

In this paper, an unconventional method of dc link bulk capacitance active reduction without ripple increase in mains-connected power conversion systems is proposed. Even though the adopted power circuitry (a bidirectional dc dc converter, terminated by a much smaller capacitance) is analogous to solutions proposed up to date, the concept of operation is quite different. Rather than controlling the current, flowing into the dc link (i.e., operating as a current controlled current sink, similarly to an active power filter), suggested solution regulates the ripple by controlling the dc link voltage (i.e., operating as a voltage controlled current sink) thus letting the grid-interfacing converter OFF the task. This allows widening of the dc link voltage loop bandwidth and, as a result, reducing the ripple for the same capacitance utilized or reducing the capacitance while maintaining the same ripple without trading off the power factor. In order to validate the proposed methodology experimentally, it is successfully applied to a single-phase off-the-shelf power factor correction pre-converter.