Optimal control for AC drive with quadratic criteria

The main result presented in this paper is the implementation of optimal control based on quadratic criteria into a low power electric drive with three-phase induction motor. The dSPACE 1104 controller has been used in order to obtain the on-line optimal solution of matrix Riccati differential equation (MRDE). Based on the optimal solution and on corresponding feedback signals, the optimal speed reference for the AC drive system is obtained. The optimal speed reference is tracked by Altivar 71 inverter, conducting to energy reduction in AC drive. In order to highlight the performances obtained by electric drive, the classical control (consisting of rotor field oriented control with PI controller) and the optimal one have been implemented by designing an adequate ControlDesk interface. The three-phase induction machine (IM) is controlled at constant flux. Therefore, the linear dynamic mathematical model of the IM has been obtained. The comparative analysis of the AC drive system conducted by the optimal control and by classical one reveals the optimal control advantages. The optimal control law provides smooth transient regimes with minimal energy consumption. The constraints of the control and state magnitude can be solved by adequate choice of the weighting matrices of the adopted performance functional. The obtained solution, by integration of the MRDE, is orientated towards the numerical implementation-by using a zero order hold. The implemented test bench system is very useful to researchers, doctoral students or experts training in electrical drive. The analysis of optimal control solution and the influences of the weighting matrices are shown through the experimental results.