Efficient state reference generation for torque control in externally excited synchronous machines

A difficult challenge in hybrid electric vehicles (HEVs) and full electric vehicles (EVs) is the torque control of externally excited synchronous machines (EESMs). Effective torque control requires an efficient solution to the state reference generation problem, which is a nonlinear non-convex optimization problem. The goal of this paper is to develop a state reference generation algorithm based on the griding of the state and output spaces. Firstly, an approximation defined over a cubic partition of the torque function with a piecewise affine (PWA) function is made. As a result, the state reference generation problem is reduced in each cube to solving a convex optimization problem. Moreover, this approach provides guarantees about the error bound introduced by the state reference generation procedure for the full operational state-space. To illustrate the effectiveness and robustness of the proposed algorithm several simulation results are presented. The obtained results show significant improvement compared with existing state-of-the-art reference generation methods.