A Direct Thrust Control Scheme for Linear Permanent Magnet Synchronous Motor Based on Online Duty Ratio Control

Linear permanent magnet synchronous motors, especially those with low inductance and short pole pitch, exhibit significant ripple in flux and thrust force under conventional direct thrust force control. Aimed at reducing ripple in the flux and the force, a duty ratio control scheme for direct thrust force control of linear permanent magnet synchronous motors is proposed. The effect of inverter voltage vectors on the flux and the thrust force is analyzed. Subsequently, a precise expression for the online computation of the required duty ratio is derived. Compared to the state-of-the-art duty ratio control, the proposed approach eliminates the need to tune gains. The proposed online duty ratio calculation is based on the selected voltage vector from the switching table and takes into account the mover's speed. The proposed approach retains the characteristics of the conventional direct thrust control in terms of fast transient and steady-state responses for both flux and thrust force. Experimental results demonstrate a faster transient response and negligible steady-state error for flux, force, and speed responses under the proposed approach when compared to the state of the art.