Optimal torque control of permanent magnet synchronous machines using magnetic equivalent circuits

In recent years, permanent magnet synchronous machines (PSMs) are often designed in a mechatronic way to obtain e.g. special torque characteristics at zero currents or maximum efficiency. These designs are often characterized by a pronounced magnetic saturation and non-sinusoidal properties. This paper describes the optimal torque control of such PSMs utilizing a magnetic equivalent circuit (MEC) model. In contrast to approaches based on fundamental wave models (dq0-models), which utilize the Blondel–Park transformation and typically consider saturation and non-sinusoidal characteristics only in a heuristic way, MEC models allow to systematically account for these effects. Given the MEC model, optimal values for the coil currents are obtained from a constrained, nonlinear optimization problem, which can be efficiently solved by exploiting the special mathematical structure of the model. The results of the optimization are used in a flatness-based torque control strategy. The performance and practical feasibility of the proposed torque control concept are demonstrated by experiments on a test stand. Finally, it is shown that using this torque control in an outer angular speed control loop also proves to be beneficial.