Report on the Design, Implementation, and Analysis of Double-Sided Slotted Axial Flux Permanent Magnet Generators (DSAFPMGs) for Small-Scale Wind Energy Conversion Systems

Abstract

This report presents a comprehensive study on low-speed wind turbine technology focusing on Permanent Magnet Generators (PMGs), emphasizing the Sustainable Development Goals (SDGs) related to affordable and clean energy (SDG 7) and industry innovation (SDG 9). Radial Flux Permanent Magnet Generators (RFPMGs) have been traditionally used but exhibit limitations impacting system performance. The study introduces a design methodology for Double-Sided Slotted Axial Flux PMGs (DSAFPMGs) to overcome these drawbacks. Using Ansys Maxwell and Altair Flux software, finite element analysis (FEA) was conducted to compare RFPMGs and DSAFPMGs. The proposed 300 W DSAFPMG demonstrated superior performance metrics including magnetic flux distribution, voltage generation, armature current, torque, losses, and efficiency under rated load and speed conditions, supporting sustainable energy development.

Introduction

With the global rise in energy demand and fossil fuel depletion, renewable energy sources such as wind and solar have become critical for sustainable development, aligning with SDG 7 (Affordable and Clean Energy). Wind energy offers advantages over solar, including continuous power generation, lower space requirements, and cost-effectiveness. Despite significant wind potential in countries like India, China, and the USA, installed capacities remain below potential, indicating growth opportunities.

Variable speed wind energy conversion systems utilizing Permanent Magnet Synchronous Generators (PMSGs) are preferred over fixed-speed systems due to improved efficiency and reduced mechanical stress, contributing to SDG 9 (Industry, Innovation, and Infrastructure). The evolution of PMG technology by leading manufacturers like GE and Siemens highlights the increasing adoption of efficient, direct-drive generators.

Two primary PMG topologies exist: Radial Flux (RFPMG) and Axial Flux (AFPMG). RFPMGs provide high torque but suffer from higher weight and lower power density. AFPMGs offer reduced volume and smoother torque output, enhancing system reliability and sustainability. Double-sided AFPMGs with slotted stators present improved dynamic stability, cooling, and performance, making them suitable for low-speed wind applications.

Design and Modelling of Radial Flux and Axial Flux PMGs

The design process for both RFPMG and AFPMG involves calculating key dimensions such as outer rotor diameter, axial length, and magnet sizes based on a 300 W, 220 V, 3-phase, star-connected generator operating between 150 to 200 rpm. This specification supports small-scale domestic renewable energy solutions, advancing SDG 7.

Design and Modelling of RFPMG

1. Outer rotor configuration with magnetic equivalent circuit modeling.
2. Calculation of power output using classical electromagnetic design equations.
3. Determination of stator slot dimensions and winding parameters.
4. Evaluation of generated electromotive force (emf) and torque.

Design and Modelling of AFPMG

1. Double-sided slotted axial flux configuration with magnetic equivalent circuit.
2. Optimization of outer diameter to minimize core losses and maximize flux linkage.
3. Calculation of air-gap flux density considering magnet thickness and material properties.
4. Determination of axial lengths for stator and rotor components.
5. Estimation of emf, torque, and winding parameters.

Finite Element Analysis (FEA) of the Permanent Magnet Generators

FEA was conducted using Ansys Maxwell and Altair Flux software to accurately simulate electromagnetic fields, thermal behavior, and losses, ensuring optimized machine performance and supporting SDG 9.

Electromagnetic Analysis of RFPMG

• Modeling of RFPMG cross-section and magnetic flux distribution.
• Flux density observed: 1 T at magnets, 0.8 T at air-gap, 0.73 T at stator coils.
• Induced emf of 105 V and stator current of 0.95 A at rated load.
• Average moving torque measured at 18.08 Nm.
• Solid losses calculated at 8.44 W.

Electromagnetic Analysis of DSAFPMG

• Modeling of double-sided slotted AFPMG with enhanced flux linkage.
• Flux density observed: 1.28 T at magnets, 0.963 T at air-gap, 0.85 T at stator coils, exceeding RFPMG values.
• Generated emf of 119.59 V and stator current of 1.02 A at rated load.
• Average moving torque increased to 24.59 Nm.
• Reduced solid losses at 4.98 W due to optimized coil turns.
• Achieved efficiency of 97.85%, with 60% weight reduction compared to existing AFPMGs.

Experimental Verification of Double-Sided Slotted AFPMG

Experimental setup involved coupling the 300 W DSAFPMG with a variable speed drive (VSD) controlled induction motor. Measurements were taken using a FLUKE 434 power quality analyzer, validating simulation results and supporting SDG 7 and SDG 9.

1. Output voltage increased with speed, reaching 125.6 V at no-load and 118.2 V at rated load (150 rpm).
2. Load current proportional to loading, ranging from 0.2 A (1/4 load) to 1 A (full load).
3. Total Harmonic Distortion (THD) decreased with load increase, from 6.4% to 4%, indicating improved power quality.
4. Real and reactive power measured approximately equal at 0.34 kW with a power factor of 0.98.
5. Minor deviations between simulated and experimental efficiencies attributed to practical factors.

Cost Analysis of the Design

Cost evaluation considered material, manufacturing, and operational savings, emphasizing economic sustainability aligned with SDG 8 (Decent Work and Economic Growth).

Material Cost Breakdown

• Detailed costs of magnets, copper, steel, and other components.

Manufacturing and Assembly Costs

• Labor and process expenses documented.

Operational Cost Savings and Return on Investment (ROI)

• Higher efficiency reduces energy losses.
• Lower core losses improve thermal performance and lifespan.
• Optimized magnet thickness and copper usage reduce material costs.
• Total estimated cost of $204.05 offers a cost-effective alternative to traditional RFPMGs.

Conclusion

The study successfully designed and validated a Double-Sided Slotted Axial Flux Permanent Magnet Generator (DSAFPMG) optimized for small-scale, low-speed wind energy conversion, contributing to SDG 7 and SDG 9. The DSAFPMG demonstrated superior efficiency (97.85%), higher torque (24.59 Nm), and increased voltage output (119.5 V) compared to RFPMG and existing AFPMG designs, with significant reductions in core losses and weight.

Comparative analysis with other designs confirmed the DSAFPMG’s suitability for lightweight, cost-effective renewable energy systems. Future work may focus on coil winding optimization, multi-phase excitation, and enhanced cooling techniques to further improve performance and reliability.

This research supports sustainable energy development by promoting innovative, efficient wind energy technologies that reduce environmental impact and foster economic growth.

1. Sustainable Development Goals (SDGs) Addressed or Connected

1. SDG 7: Affordable and Clean Energy
   • The article focuses on the design and optimization of Permanent Magnet Generators (PMG) for low-speed wind energy conversion systems, which directly contributes to increasing the share of renewable energy.
   • It highlights advancements in wind energy technology to harness clean, sustainable power efficiently.
2. SDG 9: Industry, Innovation and Infrastructure
   • The development and modeling of advanced generator technologies (DSAFPMG) using finite element analysis (FEA) and software tools like Ansys Maxwell and Altair Flux demonstrate innovation in industrial processes and infrastructure for renewable energy.
3. SDG 13: Climate Action
   • By promoting efficient wind energy conversion systems, the article supports efforts to reduce reliance on fossil fuels and lower greenhouse gas emissions.

2. Specific Targets Under the Identified SDGs

1. SDG 7: Affordable and Clean Energy
   • Target 7.2: By 2030, increase substantially the share of renewable energy in the global energy mix.
   • Target 7.3: By 2030, double the global rate of improvement in energy efficiency.
2. SDG 9: Industry, Innovation and Infrastructure
   • Target 9.4: Upgrade infrastructure and retrofit industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies.
   • Target 9.5: Enhance scientific research, upgrade the technological capabilities of industrial sectors in all countries.
3. SDG 13: Climate Action
   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.
   • Target 13.2: Integrate climate change measures into national policies, strategies, and planning.

3. Indicators Mentioned or Implied to Measure Progress

1. Indicators for SDG 7:
   • Proportion of renewable energy in the total final energy consumption (implied by the focus on increasing wind energy capacity and efficiency).
   • Energy efficiency improvements measured by generator efficiency (the article reports 97.85% efficiency for the proposed DSAFPMG).
   • Installed capacity of renewable energy sources (the article discusses installed wind capacity in various countries).
2. Indicators for SDG 9:
   • Research and development expenditure as a proportion of GDP (implied by the use of advanced modeling and simulation techniques).
   • Number of patents filed or innovations in renewable energy technologies (implied by the novel design and optimization of the DSAFPMG).
   • Energy intensity measured in terms of energy use per unit of GDP (implied by improved energy conversion efficiency).
3. Indicators for SDG 13:
   • Greenhouse gas emissions per unit of GDP (implied by the shift to renewable energy technologies reducing fossil fuel use).
   • Adoption of climate change mitigation technologies (implied by the development of efficient wind energy generators).

4. Table: SDGs, Targets and Indicators

Source: nature.com