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mum motor ef? ciencies exceeding 95% at full load, where a motor less than 1 kW typically reaches only 90%.

• As noted above, while ef? cien- cy varies with RPM, there should be a fairly broad range of RPM that maintains high ef? ciency for most applications re- quiring full or nearly full load.

• Partial power loading is the big issue for most applications, as running a motor at low power can cause a sig- ni? cant drop in motor ef? ciency. For ex- ample, motor ef? ciency can drop to less than 70% for fractional shaft power.

Electric motors – particularly PMSMs – are an important focus of our develop- ment work for NavCad in 2020. We are working on simplifying the de? nition of these drives in NavCad with electrical power as the “fuel” and generic motor curve shapes (such as “constant-torque, constant-power”) for early-stage design.

And, of course, we are deep into a pre- diction model for off-design partial load

Image: Hydrocomp ef? ciency maps!

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Marine Technology Reporter 19

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