Efficiency, Control, and Stability of Power Electronic Based SystemsIEEE COMPEL 2016 Trondheim Norway6-28-2016

Mohamed Belkhayat Ph. D.Research Engineer VI

2

Outline

• Efficiency– Various Platforms– PWM Topologies and Techniques

• Power Density

• Control– Simple feedback, feed-forward, cross coupled, multi-loop control, network control

• Stability– DC Systems– AC Systems

2

3

Efficiency: Electric Vehicles, KW Range

3

Constant Power Loads and Negative Impedance Instability in Automotive Systems: Definition, Modeling, Stability, Ali Emadi, Et Al. IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 55, NO. 4, JULY 2006

https://commons.wikimedia.org/wiki/File:AaronsPrius.jpg

4

Dream Liner 787: MW Range

4

• Electric Engine Start

• Electric Wing Ice Protection

• Electric AC

• Electric Driven Hydro-Pumps

• Elimination of Pneumatic Bleed System

• Flight Control Actuators

• Avionics

• Electric Brakes

• Cabin Air Compressor

Boeing 787 has a approximately 1 MW of Power Electronic Loads

* Future Aircraft Power Systems- Integration ChallengesKamiar J. Karimi, PhD Senior Technical FellowThe Boeing Company 2007

Artwork: https://commons.wikimedia.org/wiki/Boeing_787#/media/File:All_Nippon_Airways_Boeing_787-8_Dreamliner_JA801A_OKJ.jpg

5

Naval Platforms: ONR Global

CAPT Lynn Petersen

6

Naval Platforms: ONR Global

CAPT Lynn Petersen

7

Marine Power Systems Trends

PT

PTRedu

ctio

n G

ear

TG

TG ACGen

ACGen

Load

Motor

Load

Motor

Elec

tric

M

otor

PTG

PTG DCGen

DCGen

Load

Motor

Load

Motor

Conv

erte

r

Converter

Converter

Converter

Converter

Then - Good Stability/Power Quality Issues/Relatively Inefficient

Now - Possible Instabilities/High Power Quality/High Efficiency

Commercial Power Systems

Then - Good Stability/Power Quality Issues/Relatively Inefficient

8

Now - Possible Instabilities/High Power Quality/High Efficiency

9Efficiency Trends in Power Converters

Extreme Efficiency Power Electronics IEEE (2012)J. W. Kolar, F. Krismer, Y. Lobsiger, J. M¨uhlethaler, T. Nussbaumer, J. Minib¨ock∗

10

Power Density

11

Efficiency, Control, and Stability

Inefficient

Easy to Control

Efficient

Harder to Control

Artwork: https://commons.wikimedia.org/wiki

12

Efficiency, Control and Stability

Inefficient

Easy to Control

Efficient

Harder to Control

Artwork: https://commons.wikimedia.org/wiki

13Common Low Level Controls PWM

https://en.wikipedia.org/wiki/Space_vector_modulation

Simple Analytical and Graphical Toolsfor Carrier Based PWM MethodsAhmet M. Hava, Russel J. Kerkman, Thomas A LipoIEEE Transations on Power Electronics 1999

14

Notional Power Electronic Converter Controls

14

• Power Density

• Efficiency

• Optimum Control– PWM– ABC/DQ– Soft Start– Improved Load Step– Synchronization– Voltage Droop– Frequency Droop– Parallel Sharing– Phase Balancing– Stability

Rectifier B/B Stage Inverter

ICN

VCN

Transient Droop

Steady State Droop

Synchronization

ABC/DQPWM

Sharing/Phase Balancing

15

Notional Maritime Diesel Generators Controls

• Power Density

• Efficiency

• Optimum Control– Fast Start– Improved Load Step– Synchronization– Voltage Droop– Speed Droop– Protection– Stability

15

Engine Generator

AVRGOV

Transient Droop

Steady State Droop

Synchronization

16

Maritime Grid System Stability

• Time Domain- Systems are simulated in Time Domain

– Nonlinearities included– Voltage, frequency, and

rotor angle stability– Linearized and

eigenvalues assessed

• Frequency Domain-Systems are linearized at an operating point.

– Systems are injected in time domain or

– Transfer function are generated using Jacobian

16

TG

TG ACGen

ACGen

ES

Motor

Load

Motor

Converter

Converter

Converter

Converter

Converter

Negative Incremental Resistance

Power Electronics based systems are prone to negative impedance instability due to the constant-power load (CPL) nature and energy storage or filters present in the system.

A CPL example is a DC/AC inverter, which drives an electric motor and tightly regulates motor speed When input power voltage increases/decreases, input current decreases/increases This has a destabilizing effect on the system (source) connected to the CPL .This is referred to as “negative impedance instability”.

17

18Brief History Of Impedance Methods• 1932 Nyquist stability criterion

• 1976 Middlebrook criterion for stability of DC power converter with input filter

• 1970- Virginia Tech, NSWC, Purdue and others advanced and implemented less conservative criteria

• 1977 MacFarlane, Generalized Nyquist

• 1990 John Caroll states opposing argument criterion for distributed systems

• 1994 Yao and Davat look at the application of GN to Power systems

• 1995 Mike Williams develops suppressed-carrier injection techniques • for AC system stability but not in DQ

• 1997- Purdue University, Virginia Tech extend Middlebrook criterion to AC systems using Generalized Nyquist and DQ impedances.

• 2000-P Measurement: V. Tech Boeing/NNS, Williams (Patent), NNS/UM (Corzine) (Patent), FSU CAPS (Patent) Others

• 2010-P Positive/Negative Sequence: RPI (sun), NTNU (Molinas), others..

DC

AC

19

Impedance Based Methods:

DC Systems -• Make one perturbation (voltage/current) in the system• Measure the responses at the interface• Calculate the impedances

AC Systems -• DQ Method• Sequence, Modified Sequence • Impedance mapping, harmonic linerization (DC2ABC)• DQ2DC ideal converter

All frequencies creating instability are determined.

Benefits Over Fielded Stability Methods:• Satisfies the open architecture business model• Ensures system stability before system integration• Reduces integration and tuning cost• Provides a measure of stability in terms of margins.

Additional Applications:• Offers assessment of power quality, imbalances, and saturation effects • Facilitates control design, and EMI filter design• Provides model verification validation of critical components

Impedance Based Stability Assessment

Stand-Alone ConverterMiddlebrook

+-

vs

+v- Converter

+vL

-R

Pin Pout

i

Filter

is

vL = hc vvoc = hf vs

ZZ

vv

h hZ Z

L

s

f c

s i=

+1 /∞∞< <<-for 1/ ωis ZZ

[MIDD76C] Middlebrook, R. D., Input Filter Considerations in Design and Application of Switching Regulators,

IEEE Industry Applications Society Annual Meeting, October 11-14, 1976, Chicago, IL. IAS

DQ Impedance/Admittance Definitions

eqdS

eqdS

eqd vHiZv ∆+∆=∆ e

qdLeqd vYi ∆=∆

=

dddq

qdqqeqdS ZZ

ZZZ

=

dddq

qdqqeqdL YY

YYY

22

Distributed AC/DC Systems Stability

22

GeneratorAnd

Controls

Propulsion

Filter/Energy Storage

Propulsion

Propulsion

Propulsion

YqdLZqdL

YqdLZqdL

Ship Service

Ship Service

YqdLZqdL

Combat Load

YqdLZqdL

1

2

4

3

Filter/Energy Storage

GeneratorAnd

Controls

ZY Satisfies the Generalized Nyquist

Open Architecture Business Model

23

Measurement: DC Systems

23

Inj. Load

24Design and Implementation of Three-Phase AC Impedance Measurement Unit (IMU) with Series and Shunt Injection

24Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE

25

25

Impedance Measurement Unit (IMU)

IMU Background

Challenges: • Stability of power electronics systems• Impedance measurement needed on active

equipment

Solution: • Developed Impedance Measurement Unit • Three Year IRAD with Virginia Tech

Status: • Currently at NNS• Several Engineers were trained on IMU use• Resolved power supply stability issues on critical

systems• Testing is instituted for future platforms

Looking Ahead:• Upgrade Rating of Scaled Prototype IMU• Upgrade Software• Team with Commercial Manufacturer

26

DQ Impedance Structures Needed for Various Systems

• Given stability margins find source and load impedances

• DC case algorithms exist

• AC case involves inverse Eigen Value Problem Algorithms still in research

• Structure of DQ impedance is not always symmetric

• Better structure identification is needed

• Better Controls-to-impedance shaping is needed

26

+−

+=

sLRLLsLR

e

qdS ωω

Z

( ) ( )( ) ( )

+−

+=

ssLRsLsLssLR

ddb

qbqe

qdS ωω

Z

RL Load or Source

Unregulated Synchronous Generator

Ideal CPL Admittance in QD (Vd=0)

27

Suggested Future Topics of Research

• DC Systems: given an architecture automatically assign impedance profile requirements at the various interfaces for a stable integrated system.

• AC Systems:

• A theoretical framework is needed that ties Direct/Quadraturereference frame, Dynamic Phasors, Positive/Negative Sequence, ABC phase domain, and harmonic linearization.

• Decoupling controls and Impedance shaping

• Same as DC systems above

• Measurement: better techniques for both low and high power