Power electronics converters are essential for power generation, transmission, and distribution. The modular multilevel converter (MMC) is highly valued for its versatility, high efficiency, and robust control capabilities. Since MMC is composed of many components, its reliability is crucial for maintaining the availability of electrical power systems. The reliability of the MMC can be evaluated using different methods, such as the military handbook (MIL) and the Mission Profile (MP) methods. By comparing the reliability estimation of the MMC using the MIL and MP methods, this study offers insights into the effectiveness of these approaches. Also, it shows the significant difference in final results between the two applied methods. These findings contribute to the understanding and improvement of the reliability assessment of power electronics converters. Also, the impact of redundancy is scrutinized to make the comparison more thorough.

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Modular multilevel converters are favorable for efficiently operating high-power usages. The required number of components significantly increases when higher modularity is introduced for the given voltage level, thus reducing the system's reliability. This article suggests a mixed redundancy strategy (MRS) that combines the operational concepts using active and spare redundant submodules. It is shown that more than 50% higher B10 lifetime (the point in time when the system has a 90% probability of survival) is achievable as compared to reliability improvement using fixed-level active redundancy strategy, load-sharing active redundancy strategy, and standby redundancy strategy with the same number of redundant submodules. The tradeoff between operational efficiency and investment cost is explored to define the boundary for selecting the MRS over other redundancy strategies with varying dc-link voltages and average converter loading, considering a ten-year payback period and equivalent B10 lifetime. The change in viability boundary for the MRS is established with increasing B10 lifetime and its sensitivity to power electronic component costs and assumed failure rate. The effect of power capacity with a higher switch current rating is evaluated. Also, the Monte Carlo simulation methodology is proposed to evaluate the practicality and effectiveness of the proposed MRS scheme. Finally, the insights of this study are applied to existing literature.

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Reliable Power Electronic Systems (PES) are vital for enabling energy transition technologies of the future. Power hardware-in-the-Loop (PHIL) test bed can be used to validate such systems cost-effectively and time-efficiently. In general, the Real Time Digital Twin (RTDT) is a virtual representation of the PES and its operating environment that mimics its behavior in real-time to provide adequate flexibility to the test bed. The workflow of alternating between the prototype and twin, for instance, overcomes the dilemma of needing 100 % details (due to fast dynamics), but optimization during design choices requires cheap flexibility. In this paper, some use cases in applications of RTDT-based PHIL test bed such as fault tolerant converters, power electronic interface for green technologies, survivable all-electric ships, mission profile-based reliability testing, protection of multi terminal dc systems and reconfigurable hybrid ac-dc links is discussed. Furthermore, the co-simulation potential of real-time platforms is briefly described.@en

Power electronics converters are crucial for power generation, transmission, and distribution. The modular multilevel converter (MMC) is highly valued for its ability to handle high power levels, versatility in reconfiguration, high efficiency through small-capacity submodules (SMs), and robust control capabilities. A failure of a power electronics converter could result in disruptions in the flow of electrical power, which could have severe consequences for people and equipment relying on it. Thus, the reliability of power electronics converters is critical to maintaining the reliability of the electrical power system. Two well-known methodologies, the military handbook (MIL) and the more recent FIDES, can be used to evaluate the MMC's reliability. Both methods consider various factors to estimate the component's failure rate, resulting in different reliability parameters. In this paper, the reliability of the MMC is estimated using both methods, and the results are compared for standby and active redundancy strategies. Lastly, a generalized cost form that considers operational cost, capital cost, redundancy strategies, reliability methods (MIL and FIDES), and the MMC's annual average loading is presented.

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Modular Multilevel Converters (MMCs) find increasing applications in medium to high-voltage systems. In such systems, reliability-oriented selection of power electronic switches becomes essential because higher modularity implies an increased number of components. The trade-off between the impact of higher modularity on converter reliability is quantitatively established, corresponding to redundancy costs for the given lifetime requirements. Therefore, this paper proposes a method for an optimal choice among available market switch voltage rating for the MMC. It is shown that the sub-modules (SMs) based on 1.7 kV switches are the most suitable (instead of 1.2 kV and 3.3 kV switches) for two case studies adapting data from the medium voltage grid in The Netherlands. Moreover, the insights from these case studies are generalized to DC link voltage in the range of 10-220 kV and average loading of 1-100%. The sensitivity analysis is performed for the different failure rates (FRs), required lifetime, components cost, and energy price. Sensitivity analysis is also performed to identify the impact of FIDES and Military Handbook (MIL-HDBK) methods. The impact of converter power capacity is studied under the variable current rating. Finally, a generalized form of the proposed method is presented and applied in the published works.

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EV Fast chargers are crucial to alleviate the driving range anxiety for E-mobility applications. A typical converter load profile consists of a short high-current pulse to rapidly refill the EV battery followed by a cooling-off period once the charging is completed. Power electronic components experience thermal cycles as a result, which can hasten the degradation of such components. In this context, the reliability evaluation of the power electronic converters enabling fast EV charging is of importance. This paper presents the reliability assessment of the IGBT module in EV Fast chargers to show how the load profile of the charger impacts the device’s lifetime.@en

Power electronics converters will play a crucial role in power grid expansion. Superior advantages offered by MMC make it the most popular candidate amongst various converter topologies. However, due to a large number of components installed within MMC, reliability analysis is an unavoidable task that needs to be carried out to maximize the MMC's availability and positively affect the overall performance of the power system. To this end, applying redundancy at the converter level is one of the solutions to increase the reliability of the MMC. In this paper, the reliability of the MMC is evaluated during its useful lifetime according to various applied redundancy strategies. At the same time, it is proposed that optimal-decision making in redundancy strategy depends on the failure rate of which components are considered. It will be presented that the superiority of the applied redundancy can vary.@en

Power electronic converters (PECs) are workhorses of emerging distribution networks. PEC interfaced grids can function as flexible power corridors facilitating compact and efficient energy exchange between distribution generation, load and storage elements. Introducing adequate Reconfigurability, Modularity, and Redundancy (RMR) in such PEC-driven hybrid ac-dc distribution networks can enhance power delivery, thus enabling infrastructure savings. In this paper, an approach for implementing adequate RMR is introduced that can be applied at both converter- and system-level; therefore, the system's reliability can be improved. Furthermore, in this discussion, the impact of integrating renewable energy sources, charging stations and storage systems with the grids is considered with regard to the methodologies of applying RMR to improve the reliability. Potential applications include various power electronics converters, parallel ac-dc links, embedded PEC energy routers, dc hubs, and multi-parallel converter systems capable of regulating power flows between different nodes in the grid with fault-tolerant topologies.@en