Control and modulation strategies for high performance electric drives

Abstract

The rise of variable-speed, converter-driven electric drives has made their digital control increasingly significant in modern applications. As sustainability concerns and the global demand for electrical energy continue to grow, the need for more efficient and effective electric drives and power electronics solutions has become crucial. These challenges allow researchers and engineers to push the boundaries of technology to meet these evolving demands. This thesis focuses on enhancing the efficiency of traction AC drives, structured across two major research areas. The first area investigates advanced mathematical models, parameter estimators, and torque maximization strategies for Induction Machine (IM) drives. By integrating the proposed algorithms into conventional Field-Oriented Control (FOC) schemes, the drive achieves more accurate torque generation and overall improved performance. The second research area addresses the stringent requirements of electromobility, where electric powertrain systems must balance weight, volume, efficiency, and reliability. Emerging converter topologies, particularly the dual inverter, are explored as a promising solution. New modulation and overmodulation strategies are developed, allowing for improved efficiency and enhanced multilevel operation, which optimizes DC-bus voltage utilization—a crucial factor for battery-powered electric vehicles. This thesis is presented as a compilation of impact factor journal papers, complemented by explanatory text. It begins with an overview of motivation, theoretical background, and challenges within the two main research areas. Each paper is introduced by summarizing its motivation, contributions, results, and potential future directions. The final chapter includes the experimental validation of the proposed parameter estimators on a testbench equipped with a torque transducer and presents an improved control strategy for IM drives. The proposed approach consolidates individual contributions into a unified field-weakening control scheme, integrating energy optimization algorithms, improved mathematical models, and enhanced parameter estimators. Furthermore, the dual inverter topology is employed to exploit the benefits of multilevel operation, improving current quality and reducing both harmonic losses and torque ripple. The research has been validated through extensive experimental testing on IM drives, with all algorithms implemented in C language on a Texas Instruments DSP platform. The findings are particularly relevant for electric traction applications, including road and rail vehicles, as well as other specialized variable-speed drive applications.