Analysis of cost functions and setpoints for predictive speed control of PMSM drives

Performance of the PMSM numerical predictive control on very long horizon is studied in simulation. It is shown that the trajectories of optimally controlled system follow the well known trajectories of maximum torque per ampere and maximum torque per volt. Significant difference from these trajectories is observed only at rapid request for maximum current. We compare the numerical solution with analytically obtained solution of minimum time current control. We show that available minimum time current control algorithm do not match the observed trajectory. An idea how to achieve the same behavior using only one step ahead prediction is proposed. The time optimal current control is approximated using ad-hoc arguments. The challenge for future research is to design better minimum time current control strategy.