Passive harmonic filter design scheme for subsea cable applications with 6-pulse variable frequency drives

Parallel resonance is common in offshore distribution systems with lengthy subsea cables and variable frequency drives (VFDs). Traditional passive harmonic filter design scheme for 6-pulse VFDs is general acceptable when all filters are functioning properly, but when the interlocking control switches off all filters due to individual filter failure, the offshore system is exposed to rich harmonic content and could experience equipment malfunction or even the system shut down. A more reliable filter design scheme is urgently needed by offshore industry. A practical and effective single-tuned passive harmonic filter design scheme is proposed in this paper. The control strategy of the proposed filter design is slightly more complicated than that of the traditional one, and the conductor of each sub-filter needs to be oversized. However, the chance that all filters must be switched off due to individual filter failure is greatly reduced.