Online Degradation Fault Prognosis for DC-Link Capacitors in Multistring-Connected Photovoltaic Boost Converters Subject to Cable Uncertainties

• Published in: IEEE journal of emerging and selected topics in power electronics Vol. 13; no. 1; pp. 1107 - 1117
• Main Authors: Lu, Geye, Lin, Qiuqiong, Zheng, Dayong, Zhang, Pinjia
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.02.2025; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitors; Circuit faults; Current measurement; DC-link capacitor; Decoupling; Degradation; Electric potential; fault prognosis; Parameter estimation; Parameter sensitivity; photovoltaic (PV) application; Photovoltaic cells; Photovoltaic systems; Prognosis; Prognostics and health management; Robustness; Strings; Topology; Uncertainty; Voltage; Voltage measurement
• DOI: 10.1109/JESTPE.2024.3502255
• ISSN: 2168-6777

In the application of multistring photovoltaic (PV) power generation, each dc string has a boost converter and the degradation fault of its dc-link capacitor can cause power outage. A comprehensive fault prognosis technology is proposed using the measurable busbar voltage and per-string cable current. The challenge is to avoid the effect of multistring cable uncertainties. First, a 3-D plane <inline-formula> <tex-math notation="LaTeX">y = f </tex-math></inline-formula> is optimized with the information of the series resistance (<inline-formula> <tex-math notation="LaTeX">R_{x} </tex-math></inline-formula>) and capacitance (<inline-formula> <tex-math notation="LaTeX">C_{x} </tex-math></inline-formula>) of dc-link capacitor. The mathematical proof is presented that based on <inline-formula> <tex-math notation="LaTeX">y = f </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">R_{x} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">C_{x} </tex-math></inline-formula> are estimated separately by decoupling the cable parameter. Second, a novel degradation indicator D is proposed that combines increasing trends of both <inline-formula> <tex-math notation="LaTeX">R_{x} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">C_{x}^{-1} </tex-math></inline-formula>. The D-based evaluation sensitivity is improved compared with the single estimated parameter. Simulation verifies that the D-based performance is robust to multistring cable uncertainties and varying operating conditions of PV module and load. Online experiments upon the grid-connected platform clarify that the maximum error of parameter estimation is 1.6% and the D-based evaluation resolution relative to <inline-formula> <tex-math notation="LaTeX">R_{x} </tex-math></inline-formula> is 1.18 dis/m<inline-formula> <tex-math notation="LaTeX">\Omega </tex-math></inline-formula>. The breakthrough lies in the mitigation of uncertain cable effect using neither voltage nor current across dc-link capacitors. Convenient implementation and robust performance are emphasized.