Reliability analysis of buck converters in a household-sized low-voltage DC microgrid

Abstract

Household-sized low-voltage (LV) DC microgrids (MGs) are mostly interconnected to a platform that is called a local energy community (LEC). Each household-sized DC MG commonly consists of battery energy storage systems (BESSs), solar energy generating systems (SEGSs), AC loads, and LV DC appliances. The different AC loads operate through DC/AC power inverters which are connected to the high-voltage DC (HVDC) common bus in the LEC, while the LV DC appliances operate through DC–DC buck converters (DCBKCs) that are also linked to the same system. The DCBKCs can reduce the operating voltage to a certain level to be adapted to household-sized DC loads. To demonstrate the importance of BKCs in the household-sized LVDC MG, this paper presents the reliability analysis of BKCs by considering all dynamic and faulted operations during their used time. In general, the performance reliability of BKCs could be reduced by several factors including high short-circuit currents, dynamic voltage ripples, power losses, and their used time, which can cause a significant decrease in the power-supply reliability for LVDC loads. For the reliability analysis of BKCs, the primary objective is to formulate the rippled-voltage-dependent failure rate (RVDFR) and the short-circuit-current-dependent failure rate (SCCDFR) in the system. Secondly, a combination of the aforementioned failure rates (FRs) with the operating-time-dependent failure rate (OTDFR) is proposed to determine the system-level reliability of the BKC through a Markov-state transition diagram. Consequently, experiment results of reliability evaluation of the BKC in the DC microgrid show that i) capacitor and inductor components are vulnerable to multiple dynamic cases; ii) the diode is the least affected component of the BKC from random dynamic operations; and iii) faults at the BKC’s output have a significant impact on the working reliability of inductors, switching elements, and capacitors. Influenced by all dynamic and faulted operations during the used time, the BKC’s reliability could decrease to 50% within 6.9 years of usage, while the mean-time-between-failures (MTBF) value rapidly decreases within the first 5 working years.

Keywords

• Buck converter
• Dynamic operation
• Fault operation
• Failure rates
• Microgrid
• And reliability analysis