Sizing and Comparative Performance Evaluation of a 5 kW DC-Excited Flux Reversal Direct-Drive Wind Generator

In this paper, novel sizing design and comparative electromagnetic performance analysis of a three-phase 12-slots/16-pole 5 kW DC-excited flux reversal machine (DCFRM) intended for direct-drive wind power generator applications is undertaken. The conventional approach in machine design often depends on scarce rare-earth permanent magnet materials, posing economic challenges for overall machine cost and fault-tolerant performance. This study presents an alternative wind generator wherein the excitation is facilitated by DC field-excited coils positioned on the stator, while the rotor part is composed solely of iron material without windings. The objective is to enhance both the economic feasibility and electromagnetic performance of the DCFRM in the context of wind energy applications. This study involves a systematic analytical sizing of a 12/16 DCFRM using 2D Finite Element Analysis (FEA). Subsequently, the performance of the proposed machine is compared with that of permanent magnet-excited FRM (PMFRM), which is modeled with identical performance requirements for 5 kW direct drive wind power generation applications. The results showed that the DCFRM exhibits improved performance, specifically in terms of cogging torque and torque ripple at no-load and on-load conditions, respectively, due to the absence of intense flux focusing effects in the airgap compared to the PMFRM. Both machines display commendable overload capabilities under variable load conditions. Despite the bulkier size of the DCFRM, a noteworthy cost-saving of 34% in active materials is achieved. Overall, the power generation capacity of the DCFRM studied is considered to be an appropriate and cost-effective alternative to PMFRM for wind energy applications.