Predictive Control of Power Converters and Electrical Drives

9.4 Predictive Speed Control

One of the main advantages of MPC is the possibility to control several different variables using a single cost function. This makes possible the implementation of a predictive speed control while maintaining the stator currents under given conditions. It is desirable to consider a limitation on the magnitude of the currents and to optimize the torque by ampere ratio.

This application of MPC introduces some difficulties, such as the nonlinear model of the system, the large differences between the speed dynamics (mechanical dynamics) and the dynamics of the stator currents (electrical dynamics), and the quantization noise in the speed measurement [8].

9.4.1 Discrete-Time Model

In order to perform a speed control using MPC, the mechanical equations must be included in the discrete-time equations used for calculation of the predictions. The machine model can be summarized in the form of the following space state equation:

9.19

where

9.20

9.21

9.22

and where τ_s = L_s/R_s is the stator time constant and is the machine torque constant.

In order to obtain a more ...