Research On Flux Weakening Control Methods For Permanent Magnet Synchronous Motor

With the remarkable improvement of power electronic technology, microprocessors and the advanced AC motor control technology, the control performance of permanent magnet synchronous motor (PMSM) servo system has been better than ever before. Together with the advantages of simple structure and high efficiency, it is widely applied in the applications such as industrial manipulators, numerical control machine tools and electrical vehicles. In order to satisfy the demands of different applications, flux weakening control for PMSM is a simple but effective method for wide speed range operations.At first, the physical principle of flux-weakening for PMSM is analyzed in this paper, and two schemes for the flux-weakening control are introduced in the thesis, which are the method based on outer voltage regulation loop and the method based on single current regulator. In the high-speed flux-weakening region, the cross-coupling between d-axis and q-axis voltage effects current responses as well as the torque response obviously, especially as the speed increases. The cross-coupling effects can be offset by the feedback linearization in conventional current regulators, but the performance is enslaved by the parameter of the motor. With the purpose of improving the performance of current response in the flux-weakening regions, the main work of this thesis is concluded as follows:first, disturbance estimation and attenuation based composite control method for current-loop under the outer voltage regulation loop structure is proposed. In this part, the cross-coupling is regarded as the lumped disturbance and the nominal model is used for controller design. Disturbance observer is introduced to estimate the lumped disturbance, and the estimated value is used to reject the disturbance by the feedforward compensation to improve the current responses. Second, finite-time control technique based composite control method for current-loop under the flux weakening structure based on single current regulator algorithm is proposed. Compared with the conventional asymptotically stable systems, this control method can ensure the convergence of current tracking error to zero in finite time, which contributes to improve the torque control performance in flux weakening regions. At last, simulations and experiments are carried out to verify the effectiveness of the proposed flux-weakening control scheme which is based on the composite control method for the current loop.