  This paper presents development of an optimal feedback linearization control
(OFLC) for interior permanent magnet (PM) synchronous machines operating in a
non steady-sate operating point, i.e., varying torque and speed, to achieve
precision tracking performance and energy saving by minimizing the copper loss.
An isomorphism mapping between the dq-axes phase voltages and two auxiliary
control inputs over full ranges of torque and speed is established by the
linearization controller using the notion of orthogonal projection. The
auxiliary control inputs are defined to be exclusively responsible for torque
generation and power consumption. Subsequently, an analytical solution for the
optimal-linearization control is derived in a closed-form by applying the
Hamiltonian of optimal control theory in conjunction with the Pontryagin's
minimum principle. The optimal controller takes the maximum voltage limit and
torque tracking constraint into account while maximizing machine efficiency for
non-constant operational load torque and speed. Unlike the convectional
quadratic regulator-based control of electric motors, the proposed control
approach does not rely on steady-state operation conditions and hence it is
suitable for such applications as electric vehicles and robotics.
