Time-Optimal Model Predictive Control of Permanent Magnet Synchronous
Motors Considering Current and Torque Constraints
Abstract
In various permanent magnet synchronous motor (PMSM) drive applications
the torque dynamics are an important performance criterion. Here,
time-optimal control (TOC) methods can be utilized to achieve highest
control dynamics. Applying state-of-the-art TOC methods leads to
unintended overcurrents and torque over- and undershoots during
transient operation. To prevent these unintended control characteristics
while still achieving TOC performance the time-optimal model predictive
control (TO-MPC) is proposed in this work. The TO-MPC contains a
reference pre-rotation (RPR) and a continuous control set model
predictive flux control (CCS-MPFC). By applying Pontryagin’s maximum
principle, the TOC solution trajectories for states and inputs of the
PMSM are determined neglecting current and torque limits. With the TOC
solution, a flux linkage reference for the CCS-MPFC is calculated that
corresponds to a pre-rotation of the operating point in the stator-fixed
coordinate system. This pre-rotated flux linkage reference is reached in
minimum time without overcurrents and torque over- as well as
undershoots by incorporating current and torque limits as time-varying
softened state constraints into the CCS-MPFC. Simulative and
experimental investigations for linearly and nonlinearly magnetized
PMSMs in the whole speed and torque range show that, compared to
state-of-the-art TOC methods, overcurrents and torque over- as well as
undershoots are prevented by the proposed TO-MPC.