1

Simulation of Power Electronic Systems with

Christian Schaffner, Plexim GmbH

2

Contents

Company PleximSimulation of power electronic systems

ChallengesSystem vs. circuit simulation

Advantages of software PLECSState-space equationsIdeal switches

Control of simulation step size Variable vs. fixed time steps

Simulation of parasitic effectsDiode reverse recovery

Live Demos

3

Who We Are

Start-up in SwitzerlandSwiss Federal Institute of Technology (ETH), ZurichPlexim founded in 2002Customers in more than 25 countries5 employeesProfitable from beginning

PLECSToolbox for SimulinkSimulation of power electronics and electrical drives

4

Development of power electronic systems today

Use of traditional simulation programs:Complicate to operateConvergence problemsLong computation timeExpensive (TCO)

Implications:Need for specialized personnelProducts not optimizedLong time-to-marketExpensive end products

5

System vs. Circuit Simulation

System simulators(MATLAB/Simulink)

⊕ Easy set-up of controllers

Circuit equations must be provided

Circuit simulators(Simplorer, PSpice, Saber)

⊕ Easy set-up of circuit

Incorporation of controllers often difficult

Switch models too detailed

Requirement: Accurate and efficient simulation ofelectrical circuit and control system

PLECS

6

Simulink toolbox PLECS

Simulation of power electronic systems in PLECSEvaluation of new conceptsVirtual prototypesPerformance optimization

Controls modeled in SimulinkPost processing in MATLAB

TechnologyC++, Matlab (GUI)FLEXlm (license management)Multiple OS support

7

Customer Benefits

PLECS:Ease of useInherently robust algorithmFast simulation (factor 10...100 speed gain)Best cost-benefit ratio for most applicationsExtensibility through open model architecture

⇒ Reduced R&D costsReduced time-to-marketReduced quality costs

8

Example: Direct Torque Control

9

Working Principle of PLECS

Circuit transformed into state-variable systemOne set of matrices per switch combination

AB C

D

1s

Sw

itch

man

ager

PLECS S-function

Simulink

u

g

y

10

High Speed Simulations with Ideal Switches

Conventional continuous diode modeArbitrary static anddynamic characteristicSnubber often required

Ideal diode model in PLECSInstantaneous on/offcharacteristicOptional on-resistanceand forward voltage

11

Comparison: Diode Rectifier

Simulation with conventional and ideal switches

Simulation steps:1160 → 153Computation time:0.6s → 0.08s

12

Benchmarks

Examples from SimPowerSystemsComparison from ETH Zurich

13

Variable Time-Step Simulation: Buck Converter

Transistor conductsDiode blocks

LiLi

DiDu

Du

Di

14

Variable Time-Step Simulation: Buck Converter

Transistor opensImpulsive voltage across inductor

LiLi

DiDu

Du

Di

15

Variable Time-Step Simulation: Buck Converter

Impulsive voltage closes diode

LiLi

DiDu

Du

Di

16

Variable Time-Step Simulation: Buck Converter

Transistor openDiode conducts

LiLi

DiDu

Du

Di

17

Variable Time-Step Simulation: Buck Converter

Switch timing Problem:Diode opens too lateImpulsive voltage across inductor

LiLi

DiDu

Du

Di

18

Variable Time-Step Simulation: Buck Converter

Zero-Crossing Detection:Time-step is reducedDiode opens exactly at the zero-crossing

LiLi

DiDu

Du

Di

19

Innovation Built into PLECS

Combination of existing concepts:Power semiconductors modeled as ideal switchesCircuit as explicit differential equationsVirtual Dirac voltages for diode control

Innovation: Concepts above made feasible throughOwn algorithmsNumerical methods

Outlook:Real-time simulation

20

Variable vs. Fixed Time-Step Simulation

Variable Time-Step

⊕ Highest Accuracy

Can get slow for large system

Fixed Time-Step

⊕ Can speed up simulation for large systems

⊕ Hardware controls are often implemented in fixed time-step

Non-sampled switching events (diodes, thyristors) require special handling

Conclusion: Both simulation methods have their application

21

Handling of Non-Sampled Switching EventsD

iode

cur

rent

sD

iode

vol

tage

Non-sampledzero-crossing

Backward interpolationDiode 3 starts conducting

Forward stepForward step

Non-sampledzero-crossing

Forward stepBackward interpolationSync. with sample time

Forward step

Backward interpolationDiode 2 stops conducting

Backward interpolationSync. with sample time

Forward step

22

Standard Diode Model Characterized by Ron / Vf

Diode turn-off in different blocking conditionsTest circuit:

23

Standard Diode Model Characterized by Ron / Vf

Diode turn-off in different blocking conditionsTest circuit:

24

Dynamic Diode Model with Reverse Recovery

Behavioral Model

25

Dynamic Diode Model with Reverse Recovery

Reverse recovery current and over voltagein different blocking conditions

Behavioral diode model:

26

Competitive offerings

designed for power electronics

➼

➼

➼

↓

$➼➼PSIM

$$➼➼PSpice

$$$➼➼SABER

$$➼➼➼Simplorer

$➼➼➼SimPowerSystems

$➼➼➼➼➼➼➼PLECS

cost↓

fast↓

easy to use↓

ideal switches↓

variable time-step↓

fixed time-step↓

open architecture↓

integrated with Simulink

27

Reference Customers

Some of our customers:ABBAlstomBombardierBoschConti TEMICHiltiPanasonicPhilipsSiemensSmiths AerospaceTyco Electronic Power S.Vestas Wind Systems

RWTH AachenAalborg UniversityCERNChalmers UniversityDLRTU DresdenFlorida State UniversityGhent UniversityImperial College LondonUniversity of ManchesterPurdue UniversityWarsaw University of Technology

28

Application example: Efficiency comparison

Project at ABBAir-cooled MVdrive systemMeasurement oflosses difficultPLECS used forsimulation of

Switching lossesFilter lossesHarmonics

Source: Y. Suh, J. Steinke, P. Steimer: Efficiency comparison of voltage source and current source drive systems for medium voltage applications, EPE 2005 Photo: ABB

29

Application example: Optimum controller design

Project at ABB Corporate ResearchMultilevel AC-DC converter system with 16 stages12 switches per stage⇒ 192 independent switches

Simulink used for controlsPLECS used for electricalcircuit

Source: O. Aydin, A. Akdag, P. Stefanutti, N. Hugo: Optimum controller design for a multilevel AC-DC converter system, APEC 2005

30

Outlook

Continuous research

Behavioral device models (Q2 2006)Diode with reverse recovery

Thermal simulation (Q3 2006)Switching losses

Real-time simulation (Q1 2007)Project with ETH Zurich funded by Swiss government

Magnetic circuit simulation (Q3 2007)Saturation, hysteresis

31

Thank you

i-Math Pte Ltd (Sole Distributor for PLECS in ASEAN region)10 Ubi Crescent #06-37Ubi TechPark Lobby C

Singapore 408564Tel: (65) 6742 1250Fax: (65) 6742 1440

Email: info@i-math.com.sgWebsite: www.i-math.com.sg

For more information about PLECS, please contact us at