3. DC/DC converters and 1φmodulation

3. DC/DC converters and 1φ modulation Buck, Boost & Buck-Boost Control of voltage time area

27-JAN-2020EIEN25 Power Electronics

Devices, Converters, Control and Applications

Lund University / LTH / IEA / Avo Reinap / EIEN25 / 2020-01-27 2

L3: DC/DC converters + 1φ modulation

• Learning & understanding – simulation tools• Electric power converters

– Conversions, connections & operation quadrants• DC/DC converters – choppers

– Power flow, energy storage,– 1QC & 2QC

• Switching and modulation• Power switches – types and features

– States, commutation and power losses


Focus and perspectives• Power electronics is the study of switching electronic circuits in order to control the flow of electrical energy

H. Wang, M. Liserre, F. Blaabjerg, P. de Place Rimmen, J. B. Jacobsen, T. Kvisgaard, J. Landkildehus “Transitioning to Physics-of-Failure as a ReliabilityDriver in Power Electronics”, IEEE J. of Emerging and Selected Topics in Pow. El., vol. 2, no. 1, march 2014


Learning through simulations• Matlab: Simulink or

SimPowerSystems• LTspice IV: components

and subsystems

Switch!Switching?


From Switch to Bridge & ConverterLe

vels

Branches & phases

• One switch – one quadrant ….• … another switch but control nearly

the same– States s– Duty D– Repetition rate fsw

• More switches …– Parrallel series connection for

power need, otherwise Q2 levels & phases

• …more switching options– Modulation = carrier + modulating

signal


Electric Power ConvertersPower

connectivity

• Loads and sources at different voltage/power levels

• Converter has or can have different stages– dc-dc conversion via AC-link and transformer

provides galvanic insulation/separation– Switching at higher frequency provides size

reduction of transformers and inductors S=UI→S/Vtr ~ωBJ

DC power

Choppers

AC power

AC converters

Inverters

Rectifiers

G. Ortiz, J. Biela and J. W. Kolar, “Optimized Design of Medium Frequency Transformers with High Isolation Requirements”, IECON 2010


PEC: Conceptualization & classification• Range of power electronic

converters (PEC)– Purpose → function & control– Realization → selection of devices

and circuits• Classification according to

– Circuitry (Bridge), controllability of switches, Number of phases in AC side, …

• Modularity enables flexibility, scalability and high availability to meet the needs

• Bibliometric network connecting PEC function and application

Source converters

Networkconverters

Loadconverters

applications

power

functions

P. Purgat and J. Gerber-Popovic and P. Bauer, ”Modularity in power electronics: Conceptualization, classification and outlook”, IECON 2017 pp. 1307-1312


PEC “sides” & connections• Power switches are

connected from voltage stiff circuit to current stiff

• PEC are built with capacitive side and inductive

• Voltage is modulated in inductive side due to high impedance to the voltage transients like current modulation is in capacitive side

U

i

-

+

Ui

-

+

iU

i

U

inverters

DC converters

AC converters

rectifiers

2.1


Voltage conditioning

DC power

Voltage level adjusted by switched area [Vs]

AC power

Flux [Vs] intransformer cores

• Voltage transforming property – U2=N2/N1*U1 vs V2=D*V1 Step-down (N2<N1)– U2=N2/N1*U1 vs V2=1/(1-D)*V1 Step-up (N2>N1)

• AC: U1→ωψ1 → ωN1 → ωN2 →ωψ2 →U2 • DC: energy storage needed to boost current or voltage

N1 N2

Voltage area & flux [Vs]


DC/DC converters• Q1: storage needed to boost

current or boost voltage– Commutation and transients –

are you familiar?

• Q2: switching between two voltage levels

– Need of storage components?– Are you able to determine

power flow directions?

• Q4: pair of Q2 = bridge creating bidirectional voltage

V1=100%

V1

I1

V2

I2

Step up

Step down


DC/DC converters• Operation mode• Inductor or

transformer• Energizing

sequence– Forward: deliver

and store– Flyback: first

store then deliver

• # switches vs operation quadrants

DC/DC coverters

Linear mode Hard switching mode

Soft switching resonant mode

Zero Current Switching

Zero Voltage Switching

Non-Isolated Isolated

Forward type Buck

Flyback typeBoost

Single Switch

Multiple Switch


Commutation transients• Energizing / energizing an inductor

• Charging / discharging a capacitor

• Heating / cooling a specimen

LsRsUsItfeIIoffeIIon

dtdILRIU

tLRt

LR

1::1: 00

sRCsU

sUtfUeUoffeUUondt

dURCUU Ct

RCC

tRC

CC

C

11::1:

11

thth

tCR

tCR

thth

h CsRsPstfeoffeon

dtdC

RP thththth

11::1:

1

0

1

0

What circuit, which response?

try it out! What is difference between

Electric and thermal circuit?


Operation quadrants• Q1: u>0, i>0, T>0, ω>0• Q2: bidirectional voltage

and speed, i>0, T>0• Q2: bidirectional current

and torque, u>0, ω>0• Q4: bidirectional voltage,

current, speed and torque

M

voltagespeed

currenttorque

G

GM


Q1, Q2 & Q4 converters

• Q1-buck and Q1-boost are connected to the same “storage” inductor to form Q2 that allows bidirectional current in the inductor

• Q2 + Q2 = Q4 so that potentials va and vb can provide both bidirectional current and voltage

q1:buck

D

V1

-

+

q2:boost

q3:buck

q4:boost

q4

q1

q3

q2 u

i

eva vb


Q1: Step-down vs Step-up

1

12

2

2

21

1 V

TVDLIV

DVV

o

i

• Continuous mode IL >0

• Discontinuous mode IL ≥0

IL VL

t

off

onD*T

T

V2

- -

L

D R

V1IL

+

+

IL VL

t

off

onD*T

T

IL VL

t

off

onD*T

T

• Continuous mode IL >0

• Discontinuous mode IL ≥0

L

D

R

V1

V2

IL1

21

2

12

21

11

VLI

TDUV

VD

V

o

i


LTspice: buck vs boost• fsw=10kHz• D=50% duty• 10Ω load• Step down (left)

– 100→50V– Input pulsating

• Step up (right)– 50→100V– Output pulsating


Q2: 2-level voltage• Two level voltage gives

bidirectional current and not reversible voltage

• The mid point of the dc link voltage is used as reference ”0”


LTspice: Q2 bidirectional charger• Left: charging

D=4/5• Right: discharging

D=1/5• Driving voltage• Load current• Flow direction• Voltages and

currents on components

• Power losses


LTspice: Q2 S1→S2 & S2→S1• Instant traverse

from on-to-off an vice versa, accepted?

• The switching transient is not immediate

• The turn on is delayed but not turn off

– blanking or interlock time


LTspice vs Simulink• Ideal components, same

control and identical initial conditions .ic() gives same outcomes

• Simulink is sufficient focusing on control and process outcomes


Modulation: control of voltage area y

dttuYT

k0

0

• Control signal parameters– Switching frequency fsw =1/Ts

– Pulse width related to duty Tpw

– Pulse position Δton

• Reference voltage = voltage area defined by switch state s=0,1 and switch voltage uk

• Voltage surface formation by positive, negative or both positive and negative flank

t

uTpw

Ts

Δton

tu*

τ-

tu*

τ+

tu*

τ+ τ-

dtuy k

0

dtuyT

k

dtuy

dtuy

T

Tk

T

k

2/

2/

2/

2.2

Tyu


Carrier wave modulation

• Pulse width Modulation PWM– Pulse width Tpw → voltage time area y → desired average output

voltage u– Identification of maximum voltage area Y0 and control twice per

period for triangular-wave

• Spread Spectrum PWM– Reducing electromagnetic interference (EMI) and noise

2.3


Power Switch• Switch states

– Off, s=0, blocking– On, s=1, conducting

• Current and voltage directions

– Unidirectional vs bidirectional (reverse conducting RS)

– Forward blocking vs forward and reverse blocking (voltage)

Gate (G)

Anode (A)Collector (C)Drain (D)

Chatode (K)Emitter (E)Source (S)

Vs

Is

Uni-Is Bi-IsUni-Vs Parallel diodeBi-Vs Series diode symmetricIs

Vs

toff offon


Semiconductor devices & technologies• Semiconductor materials

– Silicon (Si), Silicon carbide (Sic), Gallium nitride (GaN)

• Semiconductor types– Un-, semi- and controlled– Bi and unipolar (field effect) FET– Junction

• Semiconductor devices (SCD)– Thyristors (SCR, GTO, Triac),

Transistors (BJT, MOSFET, IGBT)• Wide-bandgap (WBG) SCD allows

operating at higher voltages, frequencies & temperatures

109

108

107

106

105

104

103

102

102 103 104 105 106 107 108 109

31Ga

7N

14Si

6C

14Si

Hz

W

WBG


Volt-Ampere Characteristics• Reverse blocking

– Reverse leakage– Reverse breakdown

• Forward blocking– Forward leakage– Latching voltage/current– Forward breakdown

• Forward conducting– Cut-in voltage– Specific on resistance

breakdown

reverse

forward

overloadon

off

Is

Us

Diode

Switch


Ideal and Real Switch

• Switching transient takes time and causes power losses in switching devices

– Use switching delay to prevent overlapping transients in the branch

– Calculate energy losses by following switching states (conducting and blocking) and switch transitions (turn-on, turn -off)

IsVs

toff off

on

6.1

ton toffon offoff


Exercises on modulation (1)• PE ExercisesWithSolutions2019b 1.1-1.5• Determine u(t) and i(t) waveforms for all components in 1QC Buck, 1QC Boost or 2QC Buck where inductance L is either low or large and resistance is 0 or >0

• Calculate power at different sections of converter circuit


Simulation Exercise LAB:1• Ideal circuit and parameters vs impact of real parameters and inclusion of protection circuits


Forward/Flyback Inductor/Transformer

3. DC/DC converters and 1φmodulation

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