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shape of press-pack insulated gate bipolar transistors(IGBTs). With an intrinsic capacity to limit any overcurrents and a high switching frequency capability, the IGBT technology makes the drive easy to control and results in a very compact design. The main benefit of


this type of


inverter arrangement is the low level of current harmonics,


and power resulting in


reduced motor electrical losses and AC supply harmonics,


factor optimisation. Consequently, motor efficiency is high and harmonic filters are no longer necessary.


It is


claimed that a Mermaid system based on PWM-type MV7000 converters improves compactness and layout flexibility of the propulsion system as a whole and lessens installation and maintenance time and costs. Converteam’s marine technical director


Loic Leclere claims that Converteam’s PWM MV7000 drives using press-pack IGBTs have taken pod propulsion a step forward. Press-pack IGBTs are regarded by the company as among the best high voltage components available today. Te technology has already been used on recent vessels such as Norwegian Cruise Line’s St Nazaire-built, diesel-electric, propeller-driven Norwegian Epic. Te 7.25MW synchronous motors for


Europa 2 will be manufactured at the Converteam plant in Nancy, while the power converters will come from the group’s Massy drive factory. Mermaid mechanical and hydraulic parts will be produced at Rolls-Royce’s Kristinehamn facilities in Sweden, and final pod assembly and tests are scheduled to be undertaken at Nancy next spring. Te immediately preceding order for a


Mermaid system arose from the French Navy’s investment in a third Mistral-class amphibious assault, command and force projection ship. Under construction at St Nazaire, and due to be commissioned in 2012, the all-electric Dixmude is to be fitted with two 7MW Mermaid pods. Whereas PWM technology has been


chosen for Hapag-Lloyd’s Europa 2, the synchronous motors in the Dixmude will be fed by synchroconverters. Te same arrangements were adopted for the first two ships of the class, Mistral and


The Naval Architect July/August 2011 t


Tonnerre, completed in 2006 and 2007, respectively. In parallel with the Mermaid ‘pulling’


pod system, Converteam offers another design of podded electric propulsor using a ‘pushing’ propeller and based on the pump jet pod concept. Developed in concert with French naval defence group DCNS, the system is known as Inovelis and serves a similar power range to that covered by Mermaid. Compact in form and promising high efficiency due to the nature of


its integration with the hull, Inovelis employs induction motors fed by PWM converters. It is an untried system as yet. Converteam says that the choice


between Inovelis and Mermaid is dependent on the specific vessel application and owner’s criteria, and that the group’s track record in podded propulsion and electrotechnical engineering allows it to support a yard and client in defining the right pod solution and optimising integration of the propulsor with the hull. NA


p reliable


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W W W . B E C K ER - M A R I N E - S Y S T EM S. CO M 43


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