Abstract
With many advantages, modular multilevel convert (MMC) has been extensively used in high and medium voltage power transmission projects. The thermal performance and reliability of components in MMC are key issues in system operation. However, in the current research on the reliability of MMC components, there are few methods to improve service lifetime expectancy of the components. This paper proposes a balance control algorithm, based on the cumulative fatigue damage of components, feedback to the control terminal for allocating the sub-module (SM) operating state and generating trigger pulses. Finally, the effectiveness of the proposed algorithm is verified and discussed in case studies. It is found that this algorithm is able to improve the aging degree of components in the meanwhile, the improvement in MMC reliability comes at the cost of slightly increasing capacitor voltage fluctuations and total harmonic distortion (THD). Due to the limitation of capacitor thermal performance, SM capacitor banks become a weak link in MMC reliability.
Highlights
modular multilevel convert (MMC) is used in many medium and high voltage power occasions, which kept evolving with its unique modular structure and other technical advantages, and becomes the most popular voltage source converter [1,2]
The cumulative fatigue damage balancing algorithm can coordinate the lifetime of multiple components, and it is found that the capacitor becomes the weak link, which limits the reliability of the MMC
It has been demonstrated that the fatigue damage, due to various reasons, is
Summary
MMC is used in many medium and high voltage power occasions, which kept evolving with its unique modular structure and other technical advantages, and becomes the most popular voltage source converter [1,2]. Frederik Hahn et al proposed an active thermal balancing algorithm It reduced the difference in the junction temperature spread among SMs in all operating conditions without deteriorating the performance of the system [16]. Picas et al provided a new algorithm to achieve even distribution of switching losses and conduction losses in MMC, which is at the cost of slightly increasing capacitor voltage ripple [19] It is still a challenge to effectively improve capacitor thermal performance and reliability For this purpose, the contributions of this paper are mainly as follows: First of all, a lifetime balancing algorithm based on MMC cumulative fatigue damage is proposed. The cumulative fatigue damage balancing algorithm can coordinate the lifetime of multiple components, and it is found that the capacitor becomes the weak link, which limits the reliability of the MMC.
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