Asgard Subsea Gas Compression-Technology Qualification Testing With High-Speed VSD and Very Long Step-Out Cable

The power system, including variable-speed drives (VSDs), transformers, and long subsea power cables, is one of the main building blocks in the development of subsea gas compression. This paper presents results from full-scale technology qualification testing of a power system onshore where the VSD is controlling a 188-Hz 7.8-MW gas compressor motor over a simulated distance of 47 km. The extensive testing shows that it is possible to control the compressor/motor speed from start-up throughout the whole load envelope without the need for motor voltage and current feedback. By the use of estimator-based control, it is also possible to provide motor overcurrent protection. This paper shows how resonances in the long cable system can be handled by the use of optimization of the generated voltage waveform instead of using a VSD sine filter. The successful technology qualification shows applicability for subsea compressors with a rated frequency of up to 200 Hz, at least 8-MW shaft power, and a step-out distance of at least 50 km.