Enhanced rotor field oriented control of five-phase induction motor with the combined fundamental and third harmonic currents

This study focuses on development and application of rotor field oriented control (RFOC) on a five-phase induction motor with concentrated windings. Specifically, investigation is made to improve flux density, output torque and reliability of the five-phase induction motor by combining the fundamental and third harmonic currents.; According to harmonic analysis on the multiphase induction motors, the third harmonic current plays an important role in increasing flux density and output torque. Therefore one of the major objectives of this study is to utilize the third harmonic currents in the five-phase induction motor. For this purpose, a multiphase coordinate transformation and a revised dq model of the five-phase induction motor under the fundamental and third harmonic currents are established in a new d ₁q₁d₃ q₃n reference frame, which serves as the theoretical basis for RFOC of the five-phase induction motor.; RFOC is extended to the five-phase induction motor drives to generate the fundamental and third harmonic currents and to perform direct control of flux and torque. The corresponding algorithm and control scheme with the combined fundamental and third harmonic currents are developed. By adopting proper dynamic adjustment and steady state compensation, RFOC of the five-phase induction motor not only achieves high drive performance, but also realizes the desired nearly rectangular stator currents and flux. As a result, a considerable enhancement of flux density and torque is obtained.; Based on the RFOC scheme developed, a resilient current control of the five-phase induction motor under asymmetrical fault operations is proposed. This control method ensures that the five-phase induction motor operates continuously and steadily without additional hardware connections in case of loss of one or two phases, which is of importance to some specific applications where fault tolerant ability and high reliability are required.; Experiments have been conducted on a 7.5hp five-phase induction motor by using TMS320C32 DSP to systematically test and compare stator tooth flux densities and torques in the presence and absence of the third harmonic currents. The results obtained are consistent with theoretical studies and simulation analysis, which further demonstrate the feasibility and practical significance of the five-phase induction motor drives developed.