Reliability-Centered Maintenance for Modular Multilevel Converter in HVDC Transmission Application

Due to its high modularity and scalability, the modular multilevel converter (MMC) has extensively been used in the modern industry. The low reliability of MMCs, which are consisted of tens or hundreds of vulnerable submodules (SMs), directly impacts the power supply continuity of the access systems. Redundancy and preventive maintenance are two significant measures to improve MMC reliability in operation. Therefore, this article presents a reliability model of MMCs with numerous SMs, whose lifetime follows arbitrary distribution, in redundancy strategies, such as active mode and standby mode. The lifetime of SMs is the minimum of component lifetime, which is estimated by a physics-of-failure-based lifetime estimation approach. Employing this reliability model, a reliability-centered maintenance (RCM) scheme with a minimum annual maintenance cost, is proposed to implement the dynamic decision of the maintenance intervals, quantitatively considering multistate of MMC operation. The relationship among redundancy, maintenance, and cost is further discussed in case studies. The proposed reliability model and RCM scheme provide a guideline for MMC redundancy strategy selection and maintenance decision.