Sliding Mode Based Combined Speed and Direct Thrust Force Control of Linear Permanent Magnet Synchronous Motors With First-Order Plus Integral Sliding Condition

A combined speed and direct thrust force control scheme in the synchronously rotating stator flux oriented reference frame based on sliding mode control is proposed for a linear permanent magnet synchronous motor. First-order stator flux dynamics and a second-order nonlinear state-space model for the combined dynamics of speed and thrust force as system states are presented for the linear machine. These dynamic models are then utilized for synthesis of the two sliding mode control laws for flux regulation and combined speed and thrust force control. The sliding mode control laws produce the orthogonal components of command voltage in the stator flux reference frame which are then applied to the machine by a space vector pulsewidth modulated inverter. Importantly, integral action is also directly included in the control laws by using a modified first-order plus integral sliding condition. The integral action eliminates the steady-state error and provides additional restoring effort in the stator flux and speed tracking combined with thrust force control. Lyapunov stability analysis proves the global asymptotic stability of the proposed control scheme. The effectiveness of the proposed method is validated by extensive experimentation on a prototype linear machine. Practical results demonstrate excellent transient and steady-state speed control performance of the proposed scheme when compared to the state-of-the-art methods.