An Online Monitoring Technique for Capacitance of DC-link Capacitor in AC-DC-DC Switched-Mode Power Supplies

The DC-link capacitor of the AC-DC-DC switched-mode power supplies (SMPSs) is located between the DC-DC converter and the rectifier bridge circuit. When these capacitors are utilized, there is a common occurrence where the equivalent series resistance (ESR) increases and the capacitance (C) decreases progressively. When the C value of DC-link capacitor decays to a certain extent, the bus voltage of SMPS fluctuates too much, and even the output voltage drops. Since the switching frequency of switch tube is relatively high, the existing technique requires a high data sampling rate for monitoring C value, which is costly to implement and is limited in engineering feasibility. To solve this problem, an online monitoring technique for C value of DC-link capacitor in AC-DC-DC SMPSs has been proposed in this study. This technique uses a low-pass filter to filter out high-frequency signals in the input current and the bus voltage of DC-DC converter. The C value of DC-link capacitor is then obtained from the low-frequency signals. This monitoring technique is applicable for a variety of AC-DC-DC SMPSs topologies, allowing for online monitoring of the C value of DC-link capacitor, which is not constrained by the converter topologies. Also, this method proposed in this paper has a low data sampling rate and strong engineering feasibility, and can achieve the purpose of long-term monitoring of the C value of DC-link capacitor. The effectiveness of the method has been verified by simulations on different converters.