Improving Torque Control Accuracy and Dynamics for High Power or High Speed Induction Machine Drives that Inherently Operate at Low Switching-to-Fundamental Frequency Ratios

Abstract

High power applications with low switching frequencies as well as high speed applications with high fundamental frequencies operate at low switching-to-fundamental (S2F) frequency ratios. With low S2F frequency ratios, it is challenging to achieve high torque control accuracy and dynamic performance. This paper identifies control issues that yield performance degradation at low S2F frequency ratios, for traditional field oriented control (FOC) and for deadbeat-direct torque and flux control (DB-DTFC) induction machine drives. By eliminating the synchronous reference frame current regulation, DB-DTFC demonstrates advantages to achieve a more desirable torque control performance in low-S2F-ratio applications. Three progressively more accurate DB-DTFC torque models are compared in terms of torque control accuracy and computation time to FOC and standard high switching frequency DB-DTFC. A general guideline is proposed to select the most suitable model for DB-DTFC drives at an arbitrary S2F ratio for high power or high speed applications.