Abstract
Clamped-single submodule (CSSM) has DC short circuit current protection function to improve the safety and stability of high voltage, direct current (HVDC) system. In order to carry out the protection, it needs an additional number of insulated gate bipolar transistors (IGBTs) and diodes compared to the conventional half-bridge submodule (HBSM). In general, the failure rate tends to increase in proportion to the number of circuit components. Also, complex operation of the submodule may increase the failure rate, so accurate reliability analysis considering these points is required to apply CSSM in a practical HVDC system. We estimate the failure rate and the mean time between failures (MTBF) of CSSM using a fault tree. Fault-tree analysis (FTA) is possible to analyze the failure rate more accurately than the prior part count failure analysis (PCA) that considers only the number of parts, the type of parts, and the connection status of each circuit component. To provide guidelines for submodule selection under various conditions, we compare the economic cost of a CSSM with HBSM, FBSM, and clamped-double submodule (CDSM), and analyze the failure rate according to the voltage margin of the parts.
Highlights
The insulated gate bipolar transistors (IGBTs) failure rate is calculated by OR-gate combination of bipolar junction transistor (BJT) and metal oxide semiconductor field effect transistor (MOSFET) failure rate provided by MIL-HDBK-217F as given in (3) [24,25]
Adding DC short current protection improves reliability, reducing the failure rate compared to FBSM, but the failure rate is higher than half-bridge submodule (HBSM) due to the increased number of parts
clamped-single submodule (CSSM) needs an additional number of IGBTs and diodes than HBSM
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Clamped-double submodule (CDSM) was introduced in [8] It adds one IGBT, two diodes, and a capacitor to the full-bridge structure. Was introduced to reduce the number of circuit components while suppressing the effects of DC short current through capacitors and diodes [10]. When the DC short current protection function is added, it has the effect of suppressing the increase of the failure rate due to the increase in the number of parts. We analyze the failure rate of CSSM that has a DC short current protection function but has a relatively small number of components. The failure rate according to the DC short current protection function of CSSM can be found by comparing the FTA results with the traditional PCA (part count analysis) results. This paper can serve as a guideline for selecting HVDC submodules by judging the reliability and economic cost of submodules employing DC short current protection
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