ACCORDING TO FINLAND-BASEDpropulsion specialist, The Switch,permanent magnet (PM) drive traintechnology for electric propulsionbrings a powerful solution to the bigdiesel dilemma, which combinestougher environmental considerationswith a long-term perspective ofincreasing fuel costs.

PM machines could offer specialseafaring vessels the opportunity tolower operational costs by optimisingthe fuel consumption of the dieselengine. Using permanent magnet(PM) motors and generators as keyelements in advanced drive trainsallows ship owners to take advantageof a more flexible, modular, efficientand lightweight propulsion system.

OPTIMAL PERFORMANCEAccording to The Switch, PM drivetrains are ideal for the electricpropulsion of tugboats, OSVs, ferries,cruise lines, research vessels,icebreakers and more. The technologyenables ships to lower their operationalcosts by optimising fuel consumption ofthe diesel engine. It is also known forits unmatched design flexibility. Thanksto their higher power density, PMmachines can pack more power in apackage that is far more compact,lighter in weight and smaller in sizecompared with induction machines.

PM machines have proven their highreliability and durability underextremely harsh operating conditions inmany industrial applications. Forexample, they are used in windturbines, which operate in a muchharsher environment than thechallenging marine market. In directpropulsion systems, no gearbox oraccompanying slip rings and brushesare needed, as with other synchronousmachines. Therefore, the PM propulsionmachine experiences fewer failures andrequires significantly less maintenance.

SYSTEM EFFICIENCYThe company also claims that a PMmachine gives high-efficiencyperformance over the entire operatingrange, significantly cutting back onfuel consumption. The Switch's igures claim that a PM machine istypically 2-4% more efficient at fullload and 10% more efficient at partload when compared with inductionmachines. These efficiencies resultfrom a lack of current losses in therotor, the absence of an exciter, andreduced winding losses.

PM propulsion motors and theirinverters efficiently turn availableenergy into thrust. Although standardinduction motors can reach high

efficiency in a narrow band aroundtheir nominal working area, PMmotors are designed to deliver evenhigher efficiency in a much widerspeed and torque range.

A synchronous PM machine containsNeodymium-Iron-Boron (NdFeB)magnets, which are materials with avery high flux density. This makesthem ideal for variable-speed motorsand generators throughout the entirespeed range. The magnet field iscreated with almost zero rotor losses.

DYNAMIC POSITIONINGThe electric propulsion of PM drivetrains allows for extra maneuverabilityfor dynamic positioning, which makesit a ideal technology for support andservice ships like supply vessels, cruiseships or ice breakers. During dynamicpositioning, a low speed with constantacceleration and deceleration isneeded to keep the ship in placewhen adapting to weather and seaconditions. PM machines have theability to function efficiently at lowspeeds and throughout the entire loadrange. In vessels where all energy isproduced by fuel, a lower consumptionleads to an improved operationalrange and lower operational costs.

Constantly varying speeds and loadscan benefit from the active motorcooling, which keeps operating

temperatures low. This results in small,but significant, efficiencyimprovements over time.

FREEQUENCY CONVERTORSOptimised for best efficiency, thefrequency converter is based oninsulated gate bipolar transistors (IGBT)with advanced vector controltechnology. It is optimized to work withPM machines for the best overallsystem efficiency. The Switch frequencyconverters offer a modular, lightweightdesign, which enables efficient use ofspace within the vessel.

A frequency converter offers theaccurate and adjustable speed controlneeded for dynamic positioning anddemanding load cycles in offshore andspecial vessels. The high-energydensity of PM technology and theresulting decrease in rotor inertia areboth beneficial when the ship needs

Permanent magnet drive trains

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● The Switch’s figuresclaim that a PMmachine is typically2–4% more efficient atfull load and 10% moreefficient at part loadwhen compared withinduction machines

A typical permanent magnetdrive train from The Switch

high maneuverability and a DP-classpropulsion system. This results inoptimum fuel efficiency and lowerlevels of exhaust.

To handle highly fluctuating loadcycles, guarantee longer engine life, cutback on fuel consumption and reachlower exhaust values, adjustable speedcontrol is ideal. This avoids the low orno-load running of generators, whichminimises engine heat stress, reducesfuel consumption and eliminatesundesired start/stop engine cycles.

TRACK RECORDAlthough new to marine applications,The Switch adds that PM technologyhas in fact been a game changer formany years in other industries, such aswind power, where it ensures thehighest energy efficiency and lowestcost of operation. As a bonus, thistechnology helps future-proof shipswhen it comes to even the strictestenvironmental legislation.

PM machines have a proven trackrecord of efficiency and environmentalfriendliness in many demandingindustrial applications, includingmarine, and according to The Switchthey far outperform inductionmachines. Not only have PM drivetrains shown that they lower fuelconsumption and provide more power,but they are also proven to last longerand require less maintenance.Additionally, the compactness of PMdrive trains leads to significant weightand space savings.

As cost pressures mount andenvironmental regulations becomemore stringent, multipurpose servicevessels that operate primarily atpartial load conditions need a novelapproach to save on operational costs.The Switch argument is that PM drivetrain solutions are compact, with lessweight and volume than conventionaldrive trains. They offer unsurpassedflexibility and a smaller footprint for alltypes of configurations, a hugeadvantage in the shippingenvironment where space is always acritical factor. By JAKE FRITH

The Switch PMM 1000 Mshaft generator

The Switch argument is that PM drive train

solutions are compact, with less weight and volume than

conventional drive trains

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