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POWER AFFILIATES PROGRAM

POWER AFFILIATES PROGRAM

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POWER AFFILIATES PROGRAM

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  1. POWER AFFILIATES PROGRAM Rotor Designs for Small Inverter-Dedicated Induction Machines M. Amrhein and P. T. Krein University of Illinois at Urbana-Champaign

  2. Outline • Overview of induction motors and design • Design approach • Optimization process • Simulation results • Rotor assembling • Future work

  3. Induction Machines, Key Facts • Exist about 100 years • Efficient, rigid, easy to use • Low cost in manufacturing and service compared to other types of machines • Designs are well established for general purpose machines → Standardized designs, design classes (NEMA) • Designs have trade-offs to satisfy certain performance criteria

  4. Induction Machines, Key Facts • Rotor slot shapes are a key issue in the machine design • Slot shapes are optimized and well-known for standard machines • Innovative and new designs are rare • Electronic drives introduce new performance aspects • Drive technology improved (e.g., control algorithms, power electronics components)

  5. Why a New Design? • The machine designs have not been altered to take advantage of the new technology • Same motors are used for line-start applications as well as for drive applications • Machines can be optimized for operation with power electronics drives • Different performance criteria: • No line-starts • Motor operates only in low-slip regime

  6. Performance Criteria

  7. Project Idea • Idea: New designs of small induction motors optimized for use exclusively with inverters • Numerous parameters for optimization (stator-design, rotor-design, materials,...) ÞFocus on rotor slot design • Power range: ~ 3HP and less • Goal: Maximize performance with respect to • Steady-state operation efficiency • Maximum torque

  8. Design Approach • Use finite-element-method (FEM) solver to calculate machine performance, given a slot-geometry • Alter geometries, compare results using a performance function approach • Performance function should reflect efficiency

  9. Performance Evaluation

  10. Optimization Process, Generic Slot Model • Rotor slot is modeled with 14 geometric parameters • Most reasonable slot shapes can be modeled (e.g., deep bar slots and double cage geometries are possible) • Effects of closed / open slots can be simulated

  11. Optimization Process • Challenging optimization problem (14-dimensional) • A “brute force” approach with 10 values for each parameter would require 1014 test cases! • A sophisticated nonlinear approach still requires a large number of test cases • Convergence and analysis of converged solution would be an issue

  12. Optimization Process, Monte Carlo • “Solution”: Monte Carlo approach • Randomly chosen numbers are assigned to the 14 parameters within a given parameter space defined by geometric constraints • Advantages: • Broad exploration of different slot geometries • Likely to find good designs with enough test cases • Unexpected designs far from conventional ones are possible • Convergence is achieved with about 1000 test cases

  13. Simulation Results, Design Comparison • 4 possible rotor geometries • Design-01 is the yields highest performance index • Slot area of Design-01 ≈ 4 x slot area of conv. design

  14. Simulation Results, Design Comparison

  15. Simulation Results, Design Comparison

  16. Simulation Results, Area Sensitivity • Trend towards a consistent cross-sectional slot area was observed • Designs with equal area have a similar performance value q • Different bar materials yield an optimum slot shape similar to Design-01

  17. Simulation Results, Shape Sensitivity • Equal area criterion: Changes of up to 15% in parameter values do not have an effect on performance, as long as the total slot area does not change. • Conclusion: A certain amount of conductor material can be placed within a rotor to increase efficiency. Distribution of material is relatively insensitive.

  18. Rotor Assembling

  19. Rotor Assembling

  20. Rotor Assembling

  21. Experimental Setup

  22. Experimental Setup

  23. Future Work • Currently rotors are in production • Different issues need to be solved • Better way (easier) for rotor assembling • Casting process • Test procedures (how to test different rotors with a given stator for reasonable comparison) • Machine model more suitable for optimization • Full integration of the optimization process