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DC/DC converters + 1φ modulation L3: 28-JAN-2019

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  • 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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 3

    Learning through simulations• Matlab: Simulink or

    SimPowerSystems• LTspice IV: components

    and subsystems

    Switch!Switching?

    Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 4

    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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 5

    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

    Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 8

    Voltage conditioning

    • Voltage transforming property – U2=N2/N1*U1 vs V2=D*V1 Step-down (N2N1)

    • 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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 9

    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

    Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 10

    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, w

    hich response?

    try it out! What is difference be

    tween

    Electric and thermal circuit?

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 11

    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

    Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 12

    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

    1 V

    TVDLIV

    DVV

    o

    i

    • Continuous mode IL>0

    • Discontinuous mode IL≥0IL VL

    t

    off

    onD*T

    T

    IL VLt

    off

    onD*T

    T

    V2

    - -

    L

    D R

    V1IL

    +

    +

    IL VLt

    off

    onD*T

    T

    IL VLt

    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

    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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 15

    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”

    Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 16

    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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 17

    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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 19

    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

    Tk

    T

    k

    2/

    2/

    2/

    2.2

    Tyu

    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

  • Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 23

    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

    Lund University / LTH / IEA / AR / EIEN25 / 2019-01-28 24

    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