Wärtsilä LLC

The Low Loss Concept (LLC) represents a new approach in supplying power to the frequency drives for electric propulsion.

The basic motive for the design is to reduce and eliminate the need for supply (pulse) transformers to the frequency converters, especially those supplying electric propulsion.
The LLC solution is based on a common 30 degrees phase shifting transformer, which provides the power supply to the 12 pulse rectifying bridge, and thus the necessary cancelling of harmonic currents caused by the frequency converters.
 

The LLC concept has proven advantageous in several aspects

• The transformerless configuration of the LLC system results in a higher system efficiency of 2% – 3%, this is also implying a 10% lower fundamental current that is supplied from the switchboard to the frequency converter.
• The lower electric losses in the system will result in improved fuel economy and reduced need for auxiliary machinery systems.
• The introduction of the LLC transformer in the electric distribution system reduces the overall short circuit current level by 15% to 20%. This allow for a system design comprising Low Voltage (LV) components and subsequently large weight and volume reductions compared to traditional systems including transformers . For certain applications the weight reduction may be 35% to 40% compared to competing designs.
• The Total Harmonic Distortion (THD) of the voltage in a LLC system is slightly better than in a traditional 12 pulse system, and always designed to be less than 5%.
• The dual supply to the frequency converters and the four galvanic separated switchboards increase the total system availability significantly. The converter supplying the propellers will still be in operation after a switchboard failure.