Simple and robust model predictive control of PMSM with moving horizon estimator for disturbance compensation

Abstract

This paper deals with a novel robust current control scheme for PMSM drives, based on the model predictive control (MPC) theory. It has been designed a simple quadratic formulation of the reference tracking problem in order to compute the optimal commanded voltage. Considering only equality constraints allows the efficient computation of a closed-form solution which solves the minimisation problem. Authors' proposed objective function is extended to include the inequality constraints, such as current and voltage limitations, therefore, the problem indirectly penalises the violation of boundaries through a weighting strategy. However, the controller does not require any calibration effort, maintaining the application suitable for different drive systems. The increased robustness is achieved through the integration of a moving horizon estimation (MHE), which exploits the same explicit formulation obtained for the MPC, but with the objective of estimating the voltage disturbance affecting the machine. The dual estimation problem is directly integrated within the prediction step of the MPC, improving drastically the local accuracy of the nominal model prediction with further advantages in terms of precise reference tracking and disturbance rejection capabilities. The effectiveness of the proposed control is verified by mean of test-bed experiments.

Keywords

• robust control
• electric current control
• predictive control
• sampling time
• moving horizon estimation
• dual estimation problem
• disturbance rejection capabilities
• robust model predictive control
• horizon estimator
• disturbance compensation
• PMSM drives
• reference tracking problem
• optimal commanded voltage
• equality constraints
• closed-form solution
• minimisation problem
• inequality constraints
• MPC problem
• voltage disturbance
• robust current control scheme