Design and Analysis of a Fault-Tolerant Modular Multilevel Converter for the Protection and Enhanced Reliability of Offshore PMSG Wind Farms

Abstract

The growing adoption of offshore permanent magnet synchronous generator (PMSG) wind farms is necessitating strategic and fault tolerant power conversion platforms that would provide constant power under the strenuous marine environment. This paper reports the design and study of the fault-tolerant Modular Multilevel Converter (MMC) which was customized to offshore PMSG applications. In the proposed MMC, the redundancy of sub modules, fault redundancy through adaptive reconfiguration control to take control of short circuit of sub modules, and open circuit is put in proposal. The simulation of a 201 level, 5 MW, 66 kV MMC prototype is tested to confirm the operation. The converter had been tested under single and double conductor submodule faults to stable operation less than 2 % total harmonic distortion (THD) and an error on balance of the voltage noted at, less than 1.5%. A comparison of the results shows that the proposed fault-tolerant scheme increases the availability of converters by up to 18% and system efficiency by up to 3.7% as compared to the traditional MMCs. Moreover, in grid-side disturbances, the design manages dynamic stability of voltage in the range of ±5% of nominal values so that wind power transmission is made continuous. As revealed in the analysis, the proposed fault-tolerant MMC will allow improving significantly the reliability, protection, and the overall energy delivery performance of large-scale offshore PMSG wind farms.