Efficiency maps visualise the fraction of electrical input power that emerges as useful mechanical output across the operating range. They help designers identify regions of high loss and optimise control strategies.

Loss components

1. Copper loss: Resistive heating in the stator windings, proportional to (i^2 R).
2. Iron loss: Hysteresis and eddy‑current losses in the stator core, increasing with the square of electrical frequency.
3. Magnet loss: Eddy currents in the magnets; typically small for bonded magnets but can be significant for sintered magnets at high speed.
4. Mechanical loss: Friction and windage, generally speed‑dependent.

Takeaways

1. Efficiency maps guide design decisions, highlighting inefficient regions.
2. Reducing copper and iron losses yields the largest efficiency gains.
3. A well‑tuned controller can improve efficiency by operating on MTPA and field‑weakening trajectories.