DC/DC converters + 1φ modulation

L3: 28-JAN-2019

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 1

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

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 2

Focus and perspectives

• Power electronics is the study of switchingelectronic 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

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Learning through simulations

• Matlab: Simulink or SimPowerSystems

• LTspice IV: components and subsystems

Switch!Switching?

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From Switch to Bridge & Converter

• 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

Branches & phases

Leve

ls

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Electric Power Converters

• 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

Power connectivity

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

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 6

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

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 7

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 currentmodulation is in capacitiveside

U

i

-

+

Ui

-

+

iU

i

U

inverters

DC converters

AC converters

rectifiers

2.1

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Voltage conditioning

• 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

DC power

Voltage level adjusted by switched area [Vs]

AC power

Flux [Vs] intransformer cores

Voltage area & flux [Vs]

N1 N2

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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

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Commutation transients

• Energizing / energizing an inductor

• Charging / discharging a capacitor

• Heating / cooling a specimen

LsRsU

sItfeIIoffeIIon

dt

dILRIU

tL

Rt

L

R

1::1: 00

sRCsU

sUtfUeUoffeUUon

dt

dURCUU C

tRC

C

tRC

CC

C

1

1::1:

11

thth

tCR

tCR

thth

h CsRsP

stfeoffeon

dt

dC

RP thththth

1

1::1:

1

0

1

0

What circuit, which response?

try it out! What is difference between

Electric and thermal circuit?

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Operation quadrants

• Q1: u>0, i>0, T>0, ω>0

• Q2: bidirectional voltageand speed, i>0, T>0

• Q2: bidirectional currentand torque, u>0, ω>0

• Q4: bidirectional voltage, current, speed and torque

M

voltage

speed

current

torque

G

GM

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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

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 13

Q1: Step-down vs Step-up

1

12

2

2

21

1V

TVDLI

V

DVV

o

i

• Continuous mode IL>0

• Discontinuous mode IL≥0IL VL

t

off

onD*T

T

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

1

1

VLI

TDUV

VD

V

o

i

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 14

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

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Q2: 2-level voltage

• Two level voltage gives bidirectional current and not reversible voltage

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

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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

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LTspice: Q2 S1→S2 & S2→S1

• Instant traverse from on-to-off an vice versa, accepted?

• The switchingtransient is not immediate

• The turn on is delayed but not turn off

– blanking or interlock time

LTspice vs Simulink

• Ideal components, same control and identicalinitial conditions .ic() gives same outcomes

• Simulink is sufficient focusing on control and process outcomes

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 18

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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 bothpositive and negative flank

t

uTpw

Ts

Δton

tu*

τ-

tu*

τ+

tu*

τ+ τ-

dtuy k

0

dtuyT

k

dtuy

dtuy

T

T

k

T

k

2/

2/

2/

2.2

T

yu

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 20

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

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 21

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

Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 22

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

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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

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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)

Is

Vs

toff off

on

6.1