Design of Complex Vector Current Controller for High-power Induction Motor

Stator current loop control is crucial in vector-controlled induction motors, due to its direct impact on system stability. In high-power traction systems, operating at a low switching frequency is a common practice to reduce inverter losses. This operational condition imposes limitations on the controller bandwidth and introduces significant digital delay, thereby exacerbating the cross-coupling between the d-axis and q-axis of the induction motors. This leads to increased current jitter in the dynamic process and significantly slower dynamic response, thus negatively affecting the control performance of the current loop. In order to overcome these challenges, a comprehensive analysis of the cross-coupling effect was first conducted in this study, using a mathematical model of induction motors based on the complex vector concept. Then ideas on how to overcome the delay were derived through analyzing the effect of delay on the digital vector control of asynchronous motors. At last, a complex vector controller considering the delay was designed, employing the zero-pole cancellation principle. In the discrete domain, the designed controller can eliminate the coupling terms in the controller transfer function, enabling effective current decoupling of the d-axis and q-axis. Moreover, the controller system exhibits a high dynamic response speed, as the system bandwidth can be easily adjusted to a high level, taking advantage of the typical second-order system in the transfer function of the whole control system. The results of simulation and experiment reveal the good control performance of the complex vector controller proposed in this paper. Across the entire speed range, the cross-coupling error is reduced by more than 80 percentage points, while the dynamic response speed is improved by more than 45%.