A High-Efficiency Online Monitoring Strategy for DC-Link Capacitors of Multistring DC/DC Converters in Photovoltaic Applications.

The multistring topology is widely used in photovoltaic (PV) power generation applications. These dc-link capacitors of multistring dc/dc converters suffer from different ageing severities, so realizing their independent online monitoring is critical. The equivalent capacitance ( Cx ) is a key ageing indicator. First, a novel method for Cx estimation is proposed independent of both voltage and current across dc-link capacitor. The voltage of common dc bus and the output current of dc string are used. Second, a high-efficiency online monitoring strategy is proposed. The procedure is carried out daily after the conventional exits of dc strings. A set of data are collected for the linear fitting. It is proven the fitting curve has the intersection with y -axis that turns out to be the reciprocal of Cx . Simulation results clarify that the Cx estimation has high accuracy and the monitoring performance shows robustness to environment changes and load variations. Online experiments show that the error of Cx estimation can be limited within 3.6%. The novelty of proposed strategy lies in its high-efficiency characteristics that the independent online monitoring of multistring dc-link capacitors in PV applications can be achieved without extra hardware and intrusive operation.