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Some Reflections on the Field of Power Electronics
and Control of DC-DC Converters
Trey Burns
October 1, 2012
Presentation Overview

Introduction - A Brief Look Back

An Unconventional Approach to Control

Conclusion – A Brief Look Forward
Evolution of Power
Electronics

Switching Converters Have a Long History



“The Parallel Inverter”, F. Tompkins, 1932
Power Semiconductor Switches are Key Enablers

Bipolar Transistors and SCRs Introduced in the 1950s

Power MOSFETs Became Dominant in the 1980s
Wilson and Moore Codified Fundamentals in
“Basic Considerations for DC-DC Conversion
Networks”, 1966
Some Key Power Electronics
Milestones

Silicon General Introduced the SG1524
PWM IC, 1976

Middlebrook and Cuk offered “A General
Unified Approach to Modeling Switching
Converter Power Stages”, 1976

IR Introduced the HEXFET, 1979
Evolution of Power
Electronics – The Process
Circuit
Optimization
Improved
Components
•
Fundamentals Are Well Understood
•
Circuits Are Optimized Around
Components and Applications
Evolution of Power
Electronics

Past Examples of the Process

Bipolar Transistors
Proportional Base Drive

FETs

Low RDSon FETs

Synchronous Rectification
Higher Frequency Switching Converters
Synchronous Rectification
Higher Efficiency
Converters

The Process Continues – Digital Technology

Enables more Flexibility

Enables more Intelligent Control
Semiconductor Enablers
Power Switches
Thyratrons &
Ignitrons
Bipolar
Transistors
FETs
Silicon Carbide
GaN
Controllers
Discrete Analog
Components
Analog ICs
Programmable &
Application Specific
Digital ICs
The Control Challenge
Go Inside The Control Booth
I can see only
V o!
Go Inside The Control Booth
ix
I want to be here. How
do I get here? I need to
see more than Vo!
Vo/R
vc
Vo (<V)
Laws of Physics Determine How We
Move Through the State Plane
Close the Switch and Move
from (0,0) to (V,V/R)
Open the Switch and Move
from (V,V/R) to (0,0)
Three Possible Conditions
for the Buck Converter
(These Are Off Trajectories)
Large Inductor – Less Δ ix
Small Inductor –
Discontinuous Mode
Heavy Load
Light Load
Shapes of Trajectories

Dependent on Power Stage
Component Values
L, C
 Parasitic Elements (ESR, Vd, …)


Dependent on Operating Conditions
Input Voltage
 Load

Unique Steady-State Solution = f(L, C, Vin, Io, Vo, T)
This is where
we want to be!
How Should I Control the Switches to Get There?
Establish a Switching Boundary
We can now see
how to get there
from anywhere!
Transient Response Not
Constrained by Fixed Ton, Toff or T
But Steady State Response
Reverts Back to Fixed Ton, Toff or T
Heavy Load
Nominal Load
Light Load
Higher Frequency
Lower Frequency
Trajectory Shapes Changed When the Load Changed
State Trajectory Control
Applied to Boost Converters
Target voltage
“Off-Trajectory”
“On-Trajectory”
Steady state
trajectory
Off trajectories converge to
60V, 15A point, because this
is the value of the input
voltage and the load
Starting point
Different Trajectories, Same Principles
State Trajectory Control

Incorporate All System Information



Observe System Behavior




Component Values
Line and Load Operating Conditions
Determine where you are vs.
Where you want to be
Make Switching Decisions Accordingly
Take advantage of all information available and
do not constrain switching decisions
unnecessarily
Opportunities for Innovation in
Power Electronics



Architectures

Evolve to Meet System Requirements

Example – Factorized Power from Vicor
Circuits

Build on Fundamental Principles

Optimization for Applications
Components

Strive for Ideal Behavior

Energy Storage as well as Switching and Control
Opportunities for Innovation in
Power Electronics




Materials

Thermal Interfaces

Power System in Package
Design Tools

Enable Complex Physical Relationships & Dependencies

Faster Product Development Cycle Times
Manufacturing Tools

More Precision
Smaller Components

Better Control of Processes
Higher Yields, Improved Quality
Higher Levels of Integration
Technology Enablers

Semiconductor Switches

Higher Frequency, Clean Switching Transitions

Lower On Resistance

High Frequency, Low Loss Ferrite Materials

Higher Energy Density Capacitors

Higher Levels of Integration

Monolithic Switching Regulators (e.g., Volterra)

Power System on Silicon (e.g., Enpirion)

Advanced Manufacturing Processes

Digital Control Technology
Digital Power Conversion


Digital Controllers Are Being Marketed Today

Some Application Specific

Some Programmable
Digital Controllers Enable

Intelligent Nonlinear Algorithms

Stable Operation Over Temperature

Improved Noise Immunity

Adaptive Control Algorithms
Digital Power Conversion –
An Opportunity

PLDs and FPGAs as Controllers

Power System Designers Avoid the Time and Cost of ASIC
Development

Faster than Micro-Controllers

Power Supply Makers Retain Proprietary IP

Product Ideas Can Be Developed & Verified Quickly
Final Note: When approaching difficult
nonlinear problems, you may need more
than one approach to reach a solution.
Thank You for Your Attention