EIEN20vt253. DC/DC converters and 1φ modulation Buck, Boost & Buck-Boost Control of voltage time area
27-JAN-2020 EIEN25 Power Electronics
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
Lund University / LTH / IEA / Avo Reinap / EIEN25 / 2020-01-27 3
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 Reliability Driver in Power Electronics”, IEEE J. of Emerging and Selected Topics in Pow. El., vol. 2, no. 1, march 2014
Lund University / LTH / IEA / Avo Reinap / EIEN25 / 2020-01-27 4
Learning through simulations • Matlab: Simulink or
SimPowerSystems • LTspice IV: components
From Switch to Bridge & Converter Le
ve ls
Branches & phases
• More switches … – Parrallel series connection for
power need, otherwise Q2 levels & phases
• …more switching options – Modulation = carrier + modulating
signal
Electric Power Converters Power
• 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
Inverters
Rectifiers
G. Ortiz, J. Biela and J. W. Kolar, “Optimized Design of Medium Frequency Transformers with High Isolation Requirements”, IECON 2010
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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
Network converters
Load converters
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 / Avo Reinap / EIEN25 / 2020-01-27 8
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
Voltage conditioning
DC power
AC power
Flux [Vs] in transformer 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)

DC/DC converters • Q1: storage needed to boost
current or boost voltage – Commutation and transients –
are you familiar?
– Need of storage components? – Are you able to determine
power flow directions?
V1=100%
DC/DC converters • Operation mode • Inductor or
transformer • Energizing
Soft switching resonant mode
Commutation transients • Energizing / energizing an inductor
• Charging / discharging a capacitor
• Heating / cooling a specimen
Electric and thermal circuit?
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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
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
Q1: Step-down vs Step-up
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LTspice: buck vs boost • fsw=10kHz • D=50% duty • 10 load • Step down (left)
– 100→50V – Input pulsating
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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”
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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
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
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Modulation: control of voltage area y
dttuY T
k 0
– 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
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
2.3
Power Switch • Switch states
• Current and voltage directions
– Forward blocking vs forward and reverse blocking (voltage)
Gate (G)
Vs
Is
Vs
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
31 Ga
7 N
14 Si
6 C
14 Si
Volt-Ampere Characteristics • Reverse blocking
– Reverse leakage – Reverse 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)
Is Vs
toff off
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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
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Simulation Exercise LAB:1 • Ideal circuit and parameters vs impact of real parameters and inclusion of protection circuits
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Forward/Flyback Inductor/Transformer
DC/DC converters and1φ modulation Buck, Boost & Buck-BoostControl of voltage time area
L3: DC/DC converters + 1φ modulation
Focus and perspectives
Learning through simulations
Electric Power Converters
PEC: Conceptualization & classification
PEC “sides” & connections
LTspice vs Simulink
Carrier wave modulation