Motor Control For Designers (Part 5): Deriving Force Production From Magnetic Energy
by Dennis Feucht, Innovatia Laboratories, Cayo, Belize, How2Power Today, Jan 15 2026
Focus:
In two earlier articles, the author used the Lorentz force equation to derive expressions
for the force or torque produced by motors. In particular, this led us to a definition of
lambda-sub-me, the conversion factor that relates the electrical and mechanical operation
of a motor, and the associated equations using lambda-sub-me are the basis for a motor
model. There’s an alternative method, which develops motor theory from an energy
standpoint, and the author explores this method here. Among the questions explored here is
whether the energy method will yield the same expression for lambda-sub-me and possible
new revelations about PMS and other motors. In particular, the relationship between
winding inductance and torque is analyzed (relevant to variable reluctance motors). This
part also returns to the subject of motor modeling by discussing how to model multiphase
windings.
What you’ll learn:
- How to derive an expression for motor torque versus stator current using the energy method
- How to derive an expression for motor torque versus winding inductance
- How to model multiphase motor windings
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