Design Strategies for Inverter-Driven Induction Machine

1. Design Strategies for Inverter-Driven Induction Machine Dr. LongyaXu The Ohio State University Oct., 2011

2. Contents • Introduction • Recent progress in inverter driven motors and conventional induction machine • Inverter driven Induction Machine • System configuration • Basic equations • Design strategies • Sample Design and Performance Evaluation • Conclusions

3. 1. Introduction Recent progress in PM, switched reluctance, and synchronous reluctance machines has indicated a great potential in terms of inverter driven machines; Importance of designing a so-called inverter-driven electrical machine has been fully verified; Present work has focused on non-traditional machines, such as IPM and SPM, switched reluctance and synchronous reluctance machines; Traditional induction machine can not be neglected for its very low cost, simple and rugged structure, and well developed control algorithms.

4. Conventional IM operated with fixed V & F Weight Distribution in Designing Conventional IM Needed start-up characteristics (50%); Appropriate steady state characteristics, emphasizing efficiency and power factor(30%); Easy and economic manufacturing (20%)

5. 2. Inverter Driven Induction Machine System Configuration

6. IM operated with fixed V & F It is necessary to solve two additional problems: Eliminate or minimize the harmonics produced abnormal torque occurring during start-up Reduce electromagnetic noise.

7. Inverter Driven IM Design Strategies Line start-up performance under a fixed synchronous frequency and other considerations become unnecessary

8. Equations for Vector Controlled IM

9. Relating Vector Control to IM Design

10. . Observations , Under constant rotor flux control the torque production is directly proportion to For a required torque, a correct value of must be satisfied In terms of efficiency and power factor,rotor slip frequency should be small Simultaneously satisfy the required torque Te and a small slip frequency must be properly designed

11. Inverter Driven IM Design Strategies Line start-up performance under a fixed frequency and other considerations become unnecessary; Inverter can control the induction machine to operate always at a point close to the maximum torque, maximum efficiency and improved power factor; Maximums could be introduced to the sizing equation, in place of start-up torque, the conventionally defined rated efficiency and power factor.

12. Start-up current, torque and efficiency with a fixed frequency can be completely ignored; Abnormal harmonic torque at the time of starting will not occur and needs no special consideration; Restrictions imposed by the stator/rotor slot combination rules and rotor slot shape can also be lifted. Stator and rotor slot numbers, shapes, and sizes to be optimized exclusively for minimizing the leakage inductance and resistance. Effective utilization of rotor slot area can be increasedto potentially downsize IM.

13. Sizing Equations for Induction Machines = stator inner diameter = effective length of the stator core where = machine constant = rated power = rated shaft speed

14. Explanations of Machine Constant where = constant = magnetic loading = electrical loading = EMF coefficient (E/V) = stator winding factor = efficiency = power factor

15. Inverter Driven IM Design Maximum efficiency and improved power factor should be used in determining for an inverter-driven induction machine in the sizing equation. End results are: Volume of the machine can be reasonably reduced, or Power rating can be increased.

16. Preferred rotor slots for line starting conventional IM It is common to design a double cage or deep bar rotor to increase skin-effect for start-up torque Rotor Slot for Conventional Induction Machine

17. PreferredRotor Slots for Inverter Drive Induction Machine Actual area of the rotor slot can be reduced by 25- 30% than that in a conventional design without increasing the effective rotor resistance

18. Rotor Leakage Permeance vs. Rotor Slot Shape • Rotor slot preferred:

19. 3. Sample Design and Performance Evaluation 3.1 Design Objectives: 1 Base Speed: 1730 rpm Power factor : 0.8 lagging Efficiency: ~90%

20. 3.2 Main Dimensions and Parameters Calculated by IM Design Program

21. 3.3 Capacity and Performance Calculated by IM Performance Evaluation Program

22. 3.4 Verifications by Finite Element Analysis Motor 1 Stator and Rotor Laminations

23. Motor 1 Torque and Speed Characteristics

24. Magnetic Flux Density Distributions

25. Motor 2 Motor 22 Stator and Rotor Laminations

26. Motor 2 Motor 22 Speed-Torque Characteristics

27. Motor 2 Motor 22 Magnetic Flux Density Distributions

28. Dimension and Performance Summary

29. 4. Conclusions 1) Main target of designing an inverter-driven induction machine is to optimize synergetic inverter/machine package. Inverter driven IM design strategies are different from those for line starting IM; 2) An inverter-driven induction machine gains design freedom from restrictions for line start-up performance. The design is able to be more focused on the performance in quasi-steady state conditions in a much narrower slip range; 3) Main dimensions of inverter-driven induction machine are to be reduced because only the most favorable operation conditions need to be considered;

30. Conclusions (continued) 4) Rotor slot number, shape, and size is to be optimized. resulting in improved torque, rated slip, and efficiency; 5) It is possible to downsize the machine up to 25-35% without sacrificing capacity and performance; 6) Sample inverter-driven induction machine design verifies the inverter driven IM design, using finite element analysis

31. Thanks! Q & A