Decoupled d-q Axes Current-Sharing Control of Multi-Three-Phase Induction Machines

Multi three-phase drives are a particular case of multiphase systems, which are often used in high-power applications, such as wind-energy generation, naval and railway propulsion. In a multi three-phase system the electric machine is fed by more than one three-phase converter. A current sharing algorithm for multi three-phase drives allows setting unequal current references among the converters so that each of them differently contributes to the generation of the magnetic torque and flux. Suitable current sharing control systems already exist and have been presented for multi three-phase machines. This paper illustrates a current sharing technique where the contributions to the rotor flux for the three-phase inverters, related to the d-axis current, is decoupled from the contributions to the electromagnetic torque, which depends on the q-axis current. Also, the presented algorithm minimizes the Joule losses in the stator winding. Finally, the advantages of the proposed method are analyzed and confirmed by experimental tests. The effectiveness of the control strategy is validated on a scaled prototype of a quadruple three-phase starter/generator for more-electric-aircraft applications.