  This paper presents an adaptive equivalent consumption minimization strategy
(ECMS) and a linear quadratic tracking (LQT) method for optimal power-split
control of combustion engine and electric machine in a hybrid electric vehicle
(HEV). The objective is to deliver demanded torque and minimize fuel
consumption and usage of service brakes, subject to constraints on actuator
limits and battery state of charge (SOC). We derive a function for calculating
maximum deliverable torque that is as close as possible to demanded torque and
propose modeling SOC constraints by tangent or logarithm functions that provide
an interior point to both ECMS and LQT. We show that the resulting objective
functions are convex and we provide analytic solutions for their second order
approximation about a given reference. We also consider robustness of the
controllers to measurement noise using a simple model of noise. Simulation
results of the two controllers are compared and their effectiveness is
discussed.
