Direct torque and direct suspension force control of bearingless permanent magnet synchronous motor

A bearingless permanent magnet synchronous motor (BPMSM) is a multi-variable and strong-coupled nonlinear system. To solve the difficult problem of dynamic decoupling control among torque and suspension forces, the theory and method of direct torque control (DTC) for traditional permanent magnet synchronous motors are applied to the torque control of the BPMSM in the paper. With the reference of direct torque control, a double closed-loop control system, in which the inner closed-loop is radial suspension force loop and the outer closed-loop is rotor radial displacement loop, is constructed to control the radial suspension forces directly. The DTC and direct suspension force control (DSFC) algorithms based on space vector pulse width modulation (SVM) strategy are deduced, and the DTC and DSFC system for the BPMSM are designed and simulated with Matlab software. The structure of control system is simple, and control system has strong robustness. The simulation results have shown that the rotor can be suspended steadily, and torque and radial suspension forces can be controlled independently, and the system has a good static and dynamic performance.