High-Efficiency Outer Rotor Induction Machine Design for Diverse Industrial Applications

The content of this introduction paper is based on the article "For different industrial applications: Outer rotor and low speed induction machine design" published by "Journal of the Faculty of Engineering and Architecture of Gazi University".

1. Overview:

• Title: For different industrial applications: Outer rotor and low speed induction machine design
• Author: Hakan Çelik, Numan Sabit Çetin
• Year of publication: 2023
• Journal/academic society of publication: Journal of the Faculty of Engineering and Architecture of Gazi University, 38:4 (2023) 2009-2023
• Keywords: Induction machine, Outer rotor, Design, Optimization, Finite element method

2. Abstract:

"Today, with the developing new technologies, in addition to the traditional usage areas of asynchronous machines, their usage areas as motors and generators are gradually expanding. In recent years, the use of induction generator in areas such as motor/generator in electric vehicles, wind turbines and micro-hydroelectric generation has started to widespread. This study aims to design a low-speed and high-torque outer rotor induction machine that can be used in outer rotor induction motor applications and optionally as a direct-drive generator. The design, optimization and electromagnetic analysis of a 16-pole, 50 Hz frequency, 375 rpm synchronous speed, 1 kW outer rotor induction machine were carried out and six different models were developed for the analyses in this study. One slot type and 72 slot were used in the stator designs, 59 slot and three different slot types were used in the rotor design. Copper and Aluminum materials were preferred for the squirrel cage rotor and the study was carried out with the Ansys Maxwell electromagnetic package program. In the study, machine foundation sizes, air gap and slot dimensions were optimized to obtain the highest efficiency using the Rmxprt-optimetrics module. Afterwards, electromagnetic analyzes were performed using the Finite Element Method. As a result of the analyzes made for the motor operating area of the machine, an efficiency higher than the efficiency of 8-pole inner rotor asynchronous motors with 1.1 kW power in IE2 and IE3 classes according to IEC 60034-30-1 was obtained. According to this result, it was found that an outer rotor, low speed and high torque induction machine can be produced and used as a motor."

3. Introduction:

Asynchronous machines, also known as induction machines, are experiencing increased popularity and expanding applications beyond traditional industrial uses to include motor and generator roles in emerging technologies. Specifically, their application as induction generators in electric vehicles, wind turbines, and micro-hydroelectric systems has become increasingly prevalent. This research focuses on Outer Rotor Induction Machines (DRAMAK), aiming to address the growing demand for low-speed, high-torque machines suitable for direct-drive applications and various industrial contexts. While conventional Inner Rotor Asynchronous Machines (İRAMAK) are widely used, DRAMAKs, historically limited to applications like cooling fans, are gaining attention, particularly for electric vehicle powertrains. This study introduces a novel DRAMAK design, emphasizing its potential for high efficiency and performance in demanding industrial applications.

4. Summary of the study:

Background of the research topic:

The expanding application landscape of asynchronous machines, driven by technological advancements, necessitates exploring and optimizing machine designs for diverse operational requirements. The increasing demand for motors and generators in sectors like electric vehicles and renewable energy systems highlights the importance of efficient and adaptable machine technologies.

Status of previous research:

Prior research on DRAMAKs has largely focused on single-phase motors for low-performance applications like ceiling fans. These designs often exhibit low efficiency and high slip. While studies have explored performance improvements through various techniques, a gap exists in the literature concerning high-efficiency, three-phase DRAMAK designs suitable for industrial applications and direct-drive generator systems.

Purpose of the study:

This study aims to design and optimize a three-phase, low-speed, high-torque, and high-efficiency outer rotor induction machine. The intended applications include motor/generators for electric vehicles, direct drive generators in wind turbines and hydroelectric applications, and fan motors.

Core study:

The core of this research involves the analytical design, optimization, and 2D Finite Element Analysis (FEA) of a 1 kW, 16-pole outer rotor induction machine operating at 50 Hz. Six distinct models were developed and analyzed using Ansys Maxwell software. The study investigates the impact of varying rotor slot types (round, drop cage, rectangular) and squirrel cage materials (copper and aluminum) on machine performance, with a focus on achieving high efficiency according to IEC 60034-30-1 standards.

5. Research Methodology

Research Design:

The research employs a multi-faceted approach encompassing analytical design, parametric optimization, and finite element analysis. Initially, an analytical design framework was established, followed by optimization using the RMxprt optimetrics module within Ansys Maxwell to maximize efficiency. Subsequently, 2D Finite Element Analysis (FEA) was conducted using Ansys Maxwell to validate the analytical models and assess electromagnetic performance. A 3D mechanical design was conceived based on the 2D machine geometry for comprehensive visualization. Six distinct machine models were designed, systematically varying rotor slot geometries and cage materials to evaluate their respective impacts.

Data Collection and Analysis Methods:

Data collection and analysis were primarily conducted using the Ansys Maxwell software suite. The RMxprt optimetrics module facilitated the optimization of stator and rotor dimensions, air gap, and slot parameters. Electromagnetic analyses were performed using 2D FEA to simulate machine behavior under motor operating conditions. Performance metrics such as efficiency, torque, power factor, and current characteristics were extracted from the simulations and compared across the six models. The results were then evaluated against the IEC 60034-30-1 standard for efficiency classification.

Research Topics and Scope:

The research specifically focused on the design and optimization of a 1 kW, 16-pole, three-phase outer rotor induction machine. The scope included:

• Investigating the influence of three different rotor slot types: round (Tip I), drop cage (Tip II), and rectangular (Tip III).
• Analyzing the performance with two different rotor cage materials: copper (Cu) and aluminum (Al).
• Optimizing machine parameters for maximum efficiency using the RMxprt optimetrics module.
• Verifying analytical designs through 2D electromagnetic analysis using FEA.
• Assessing the efficiency class according to IEC 60034-30-1 standard (IE2 and IE3 efficiency classes).

6. Key Results:

Key Results:

The analysis revealed significant performance variations across the six designed models. Key findings include:

• Highest Efficiency: The M3 model, featuring a drop cage slot (Tip II) and copper cage material, achieved the highest efficiency of %η=78.38.
• Highest Torque and Best Power Coefficient: The M2 model, utilizing a round slot (Tip I) and aluminum cage material, demonstrated the highest torque (Tm=27.36 Nm) and best power coefficient (Cosp=0.73). This model also exhibited the lowest speed (nr=348.99 rpm) and a high efficiency of %η=74.75.
• Material and Slot Type Impact: The choice of rotor cage material and slot type significantly influences machine performance, particularly efficiency and torque characteristics. Copper generally yielded higher efficiency, while round slot configurations contributed to higher torque in the analyzed models.

Figure Name List:

• Figure A. Outer rotor induction motor mesh operation and 2D FEA
• Figure 5. M1 Hava aralığı-verim optimizasyon grafiği (M1 Air gap - efficiency optimization graph)
• Figure 7. Eşdeğer devre parametreleri; a) R1 ve R2, b) X1 ve X2, c) Xm (Equivalent circuit parameters a) R1 and R2, b) X1 and X2, c) Xm )
• Figure 8. Faz akımları (Phase current)
• Figure 9. M1 Tork-Hız eğrisi (M1 torque-speed graphic)
• Figure 10. Tork değerleri (Torque values)
• Figure 11. a) Toplam kayıplar, b) Detaylı kayıp oranları (a)Total losses, b) Detailed loss rates)
• Figure 12. a) Verim b) Güç faktörü (a-Efficiency, b-Power factor)
• Figure 13. M3 Mesh işlemi ve M5 Manyetik alan dağılım (M3 Mesh operation and M5 magnetics field disturibition)
• Figure 14. Bakır kafesli modellerin manyetik akı yoğunluğu (Magnetic flux density of copper cage models in)
• Figure 15. Alüminyum kafesli modellerin manyetik akı yoğunluğu (Magnetic flux density of aluminium cage models)
• Figure 16. Tork-zaman eğrisi; a) M-M2, b) M3-M4, c) M5-M6, Akım zaman eğrisi; d) M1-M2, e) M3-M4, f) M5-M6 (Torque-time graphic; a) M1-M2, b) M3-M4, c) M5-M6, Current-time graphic; d) M1-M2, e) M3-M4, f) M5-M6)
• Figure 17. Hız-Zaman eğrileri (Speed-time graphic)

7. Conclusion:

This study demonstrates the feasibility of achieving high efficiency in Outer Rotor Induction Machines (ORIM) with a high pole number. The research highlights the novelty that a 16-pole 1kW ORIM can be manufactured with an efficiency exceeding the limits of 8-pole 1.1kW Inner Rotor Induction Machines (IRIM) of IE2 and IE3 efficiency classes according to the IEC 60034-30-1 standard. The findings suggest that outer rotor, low-speed, and high-torque induction machines are viable for production and practical application as motors, offering a promising avenue for advanced industrial and electric vehicle drive systems.

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9. Copyright:

• This material is a paper by "Hakan Çelik, Numan Sabit Çetin". Based on "For different industrial applications: Outer rotor and low speed induction machine design".
• Source of the paper: https://doi.org/10.17341/gazimmfd.937127

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