Analysis of the limitations of conventional direct thrust control scheme for linear permanent magnet synchronous motors

A rigorous mathematical analysis of the conventional direct thrust control scheme for linear permanent magnet synchronous motor is presented. The main inspiration for direct thrust control scheme is the direct torque control algorithm for the rotational permanent magnet synchronous motor which provides a reasonably good torque and flux response. However in case of linear permanent magnet motors, the control performance of the conventional direct thrust is significantly compromised, due to the limitations of this algorithm. A comprehensive mathematical analysis of these limitations of the conventional direct thrust control scheme for linear permanent synchronous magnet motor is carried out in this work. In addition a novel state space model for linear permanent magnet synchronous motor in stator flux reference frame is proposed. This novel state space model provides bases for the formal mathematical derivation of a modified direct thrust control algorithm. The theoretical conclusions are validated experimentally. Moreover the proposed state space model is also tested for its improved performance with negligible ripple in thrust and flux responses by its practical implementation in the laboratory.