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 N and N Harish Suryanarayana was partially funded by a fellowship provided by ABB Inc.

DC Microgrids Source: ESRDC - USC

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

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

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

Stability

Generalized Immittance

The Design Spiral

Optimization Based Design

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

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

Generation System

Converter Module

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

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

Metamodeling Consider an simple inductor …

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

Inductor Metamodel

Of Interest …

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

Challenge: Core Loss MSE Model Modification Observation

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

Challenge: Poles The limiting factor - leakage

Metamodel Formulation

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!

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

Specifications - Transient

Specifications - Distortion

Specifications - Stability

Design Space Control Parameters Passive Components

Fitness Function The fitness function is constructed as follows:

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

Sample Design

Transient Design Validation

Stability Design Validation