1. S.D. Sudhoff, H. Suryanarayana* School of Electrical and Computer Engineering Purdue University *ABB PECI 2016 Thoughts on System Level Design of DC Microgrids This work was supported by the Office of Naval Research (ONR) through Grant N00014-08-1-0080 and N00014-14-1-0160 Harish Suryanarayana was partially funded by a fellowship provided by ABB Inc.

2. DC Microgrids Source: ESRDC - USC

3. Steady-State Power Flow Multiple Generators (2 main, 2 aux) Energy Storage (?) Propulsion (2) Radar (1) Weapon Systems (?)

4. Transient Constraints Transient specifications are based on MIL-STD-704F Start-up constraintTransient event constraint

5. Distortion Constraints The rms voltage ripple at each bus is subject to a limit The rms current ripple going into each component, when supplied by / supplying an ideal source / ideal load is subject to a limit

6. Stability

7. Generalized Immittance

9. The Design Spiral

10. Optimization Based Design

11. Consider a Trivial System Minimize metrics (mass, loss, …) subject to all constraints (transient, distortion, stability, …) being met

12. Reducing Dimensionality Vendor –Power Electronics Building Block (PEBB) Fixed switching frequency Fixed gate drive, snubber Shock, vibration, thermal Control platform System Integrator –Programmable controls –Exterior passives

13. Generation System

14. Converter Module

15. Degrees of Freedom Machine: 1 at 20 DOF Inductors: 5 at 10 DOF Capacitors: 4 at 4 DOF Transformers: 1 at 15 DOF Control gains: 10 DOF Total: 109 DOF

16. Further Reducing Dimensionality Target: Power Magnet Components Approaches –Catalogs –Densities –Metamodels

17. Metamodeling Consider an simple inductor …

18. Scaling To scale –Dimensions, areas, volumes, mass: –Current, current density: –Power, energy, time: –Time, frequency: Not scaled –Magnetic flux density –Voltage

19. Inductor Metamodel

20. Of Interest …

21. Scaled Machine Design To scale –Dimensions, areas, volumes, mass: –Force, torque: –Current, current density: –Power, energy, time: –Frequency, speed Not scaled –Magnetic Flux density –Voltage Base

22. Challenge: Core Loss MSE Model Modification Observation

23. Challenge: Poles Stator backiron volume decreases Stator end conductor volume decreases Rotor backiron volume decreases Increase in loss with frequency compensated for by decrease in volume

24. Challenge: Poles The limiting factor - leakage

25. Metamodel Formulation

26. Degrees of Freedom Machine: 1 at 1 DOF Inductors: 5 at 2 DOF Capacitors: 4 at 4 DOF Transformers: 1 at 1 DOF Control gains: 10 DOF Total: 18 DOF - Piece of Cake Rubarb Pie!

27. Back to Our Test System… Minimize metrics (mass, loss, …) subject to all constraints (transient, distortion, stability, …) being met

28. Specifications - Transient

29. Specifications - Distortion

30. Specifications - Stability

31. Design Space Control Parameters Passive Components

32. Fitness Function The fitness function is constructed as follows:

33. Results of Optimization The optimization routines were evaluated using an initial population of 2000 individuals for 80 generations.

34. Sample Design

35. Transient Design Validation

36. Stability Design Validation