HIGH POWER DENSITY ELECTRIC MOTORS FOR MARINE APPLICATIONS




An electric motor that features some of the highest power density currently available is being developed for marine applications, writes Dag Pike.

UK based electric motor experts Equipmake is planning to expand into the marine market. “We see the application of our technology being mainly applicable in niche sectors and the marine sector with its new focus on developing ‘green’ solutions is one of these,” commented the managing director of Equipmake, Ian Foley.

The company claims that its motors are the most power dense in global series production and the ‘spoke architecture’ design of the motors was inspired by Foley’s development of a flywheel-based hybrid system for the Williams F1 team, which was effectively a composite electric motor. The permanent magnet motors use a spoke architecture where the magnets of the rotor are arranged like the spokes of a wheel which is claimed to give the motors a major cooling advantage. The arrangement enables the magnets within the rotor to provide a much greater surface area for cooling, and as such, power density can be greatly increased over traditional electric motor configurations. This arrangement gives the motor designers the option of incorporating either a very high power density to the motors or it enables them to be made with less expensive materials in order to achieve a given power density.

At this stage of development Foley says, “The big advantage that our motors can offer is their light weight and this means that in the marine sector the main application that we can see will be for performance craft where weight can be critical to performance. By reducing the weight of the motor it will enable designers to increase the weight and size of the battery packs that are used to power them and thus increase the overall performance”.

The company has now launched two compact motors for marine applications, which both use the spoke architecture. The APM 120 has peak power of 125kW at 12,000rpm, continuous power of 75kW and peak torque of 130Nm. Weighing just 14kg, it has a power density of just under 9kW per kilogram. With an integrated gearbox, it measures 200mm in length and 170mm in diameter. The APM 200 has peak power of 220kW at 10,000rpm, continuous power of 110kW and peak torque of 450Nm. Weighing just 40kg, it has a power density of over 5kW per kilogram. With an integrated gearbox, this latter motor measures 247mm in length and 318mm in diameter.

The high speeds at which these motors operate means that there is a need to have a gearbox to reduce the speeds to a useable level for marine work. For this purpose Equipmake uses an epicyclic gearbox that is both compact and lightweight. Both of the marine motors can supplied with this gearbox and the design allows for the motors to be installed either vertically or horizontally.

“We can also make all of the supporting power control electronics, including its own high-performance inverter which incorporates the latest silicon carbide diode technology to improve power capability and enable the inverter to run at high switching frequencies.” commented Foley. “For the future we have set our sights on developing larger versions of these motors and at this stage we are looking at motors of 400 kW which should enable us to target a much wider sector of the market particularly the workboat sector. For larger vessels the application of these unique motors is likely to be for powering auxiliary systems but we do not see any specific limitations in size for this innovative motor technology.”

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