05 Power Electronics

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26 Terms

1
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Which fields are part of power electronics?

  • Solid State Physics

  • Control Theory

  • Systems

  • Circuit Theory

  • Simulation

  • Modules

2
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What are some examples of power electronics?

  • DC/DC Converters (300 W, 2 phases, conversion of 48 V DC to 12 V DC, for voltage supply)

  • Inverters (2 MW, 6 phases, creation of multiple sinusoidal voltages, supple of multi-phase machines)

3
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How is a Power Electronics Circuit structured?

  • Composed of a low and a high power system

  • Isolated from one another by a Galvanic Isolation (no conductors inbetween)

  • Low Power System: Singal electronics + control

  • High Power System: Electronics + Converter and Filters

<ul><li><p>Composed of a low and a high power system</p></li><li><p>Isolated from one another by a Galvanic Isolation (no conductors inbetween)</p></li><li><p>Low Power System: Singal electronics + control</p></li><li><p>High Power System: Electronics + Converter and Filters</p></li></ul><p></p>
4
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What kind of Voltage Regulators are there and what is their goal?

  • They aim to keep voltage constant

  • Voltage Regulator with Series Resistance

  • Voltage Divider (Regulator with Parallel Resistance)

  • Regulator with Zener Diode

  • Regulator with Zener Diode and Transistor

5
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<p>What is an Ideal Votlage Source in Power Electronics?</p>

What is an Ideal Votlage Source in Power Electronics?

  • Constant Voltage regardless of the current through it

  • Zero Internal Resistance

  • Infinite Power Capability

<ul><li><p>Constant Voltage regardless of the current through it</p></li><li><p>Zero Internal Resistance</p></li><li><p>Infinite Power Capability</p></li></ul><p></p>
6
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How does a Voltage Source with Series Resistance look like?

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7
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How does a Voltage Divider look like?

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8
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How does a Voltage Regulator with Zener Diode looks like?

  • Uses the breakdown property of a Zener diode to regulate the voltage

<ul><li><p>Uses the breakdown property of a Zener diode to regulate the voltage</p></li></ul><p></p>
9
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How does a Voltage Regulator with Zener Diode and transistor looks like?

  • Improves the line and load regulations using the gain factor β of BJTs

<ul><li><p>Improves the line and load regulations using the gain factor β of BJTs</p></li></ul><p></p>
10
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What can MOSFETs be used for in Power Electronics?

  • As Unipolar Power Output Stage

<ul><li><p>As Unipolar Power Output Stage </p></li></ul><p></p>
11
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What is the characteristic of a MOSFET used as Unipolar Power Output Stage?

  • This basically means that a MOSFET in Power Electronics can be modelled by means of a switch

<ul><li><p>This basically means that a MOSFET in Power Electronics can be modelled by means of a switch</p></li></ul><p></p>
12
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What is the characteristic of a MOSFET modelled by means of a switch?

  • Either is open or closed

<ul><li><p>Either is open or closed </p></li></ul><p></p>
13
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What is the characteristic of a MOSFET modelled by means of a Switch, a Resistor and a Diode?

  • Either open or with current flowing through the diode and scalated by the resistance

<ul><li><p>Either open or with current flowing through the diode and scalated by the resistance</p></li></ul><p></p>
14
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What is a half bridge?

  • Arrangement of two switches (MOSFETs or IGBTs) in series across a DC voltage source, in which the point between switches acts as the output terminal

  • Very low-loss operation possible

  • 4 cases are possible:

    • Both ON = 1: short-circuit and destructive breakdown

    • Both OFF = 0: output voltage depending on the load connected to it and the circuits previous state

    • ST ON and SB OFF: output terminal connected directly to the positive terminal of the input voltage source. Therefore Vout​ = Vin​

    • ST OFF and SB ON: Vout = 0

  • Basically, create AC out of a DC source by alternating states (creates a sqaure wave)

<ul><li><p>Arrangement of two switches (MOSFETs or IGBTs) in series across a DC voltage source, in which the point between switches acts as the output terminal</p></li><li><p>Very low-loss operation possible</p></li><li><p>4 cases are possible:</p><ul><li><p>Both ON = 1: short-circuit and destructive breakdown</p></li><li><p>Both OFF = 0: output voltage depending on the load connected to it and the circuits previous state</p></li><li><p>S<sub>T</sub> ON and S<sub>B </sub>OFF: output terminal connected directly to the positive terminal of the input voltage source. Therefore <span>V<sub>out</sub></span>​ = <span>V<sub>in</sub></span>​</p></li><li><p>S<sub>T</sub> OFF and S<sub>B </sub>ON: V<sub>out </sub>= 0</p></li></ul></li><li><p>Basically, create AC out of a DC source by alternating states (creates a sqaure wave)</p></li></ul><p></p>
15
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What is there to see about a Half Bridge + LED + Resistor?

  • Square current wave made from DC source to turn on the LED

<ul><li><p>Square current wave made from DC source to turn on the LED</p></li></ul><p></p>
16
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What is there to see about a Half Bridge + LED + Inductance?

  • Similar to the resistance variant, but with a traingular wave

<ul><li><p>Similar to the resistance variant, but with a traingular wave</p></li></ul><p></p>
17
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What is there to see about a Half Bridge + Inductance + Resistance?

  • Creates also a triangular current wave as a function of switching periods, due to the inductance resisting the current flow

  • Used as buck converter

<ul><li><p>Creates also a triangular current wave as a function of switching periods, due to the inductance resisting the current flow</p></li><li><p>Used as buck converter</p></li></ul><p></p>
18
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What is PWM?

  • Pulse Width Modulation

  • Lowers the average power delivered by a source by means of the duty cycle (percentage of time period in which the signal is ON)

  • Basically, alters the frequency of the power input by the source until the wanted output power is reached

<ul><li><p>Pulse Width Modulation</p></li><li><p>Lowers the average power delivered by a source by means of the duty cycle (percentage of time period in which the signal is ON)</p></li><li><p>Basically, alters the frequency of the power input by the source until the wanted output power is reached </p></li></ul><p></p>
19
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How does the signal generation for PWM work?

  • A serrated carrier signal c(t) is compared with the modulating signal d(t), dividing the outputs at any point in 2 and therefore allowing to switch between states

  • c(t) > d(t) for a given t means OFF in switching terms

  • The same holds the other way around

<ul><li><p>A serrated carrier signal c(t) is compared with the modulating signal d(t), dividing the outputs at any point in 2 and therefore allowing to switch between states</p></li><li><p>c(t) &gt; d(t) for a given t means OFF in switching terms</p></li><li><p>The same holds the other way around</p></li></ul><p></p>
20
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How is the error modelled?

  • As d(t) - ST

  • As a weird combination of square wave and trig wave

<ul><li><p>As d(t) - S<sub>T</sub></p></li><li><p>As a weird combination of square wave and trig wave </p></li></ul><p></p>
21
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What are buck converters?

  • Power Electronics arrangements that can convert a DC voltage Vin to a lower Vout

  • They have synchronous and asynchronous embodiments

<ul><li><p>Power Electronics arrangements that can convert a DC voltage V<sub>in</sub> to a lower V<sub>out</sub></p></li><li><p>They have synchronous and asynchronous embodiments</p></li></ul><p></p>
22
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<p>How is an asynchronous buck converter built? How does the characteristics of the asynchronous buck converter look like?</p>

How is an asynchronous buck converter built? How does the characteristics of the asynchronous buck converter look like?

  • Switch + Diode + Inductance + Capacitor + Resistance

  • Chopped voltage signal, which is then converted into a smoot voltage signal due to the capacitor and the inductance (the capacitor smoothes the voltage, the inductance chops the current)

<ul><li><p>Switch + Diode + Inductance + Capacitor + Resistance</p></li><li><p>Chopped voltage signal, which is then converted into a smoot voltage signal due to the capacitor and the inductance (the capacitor smoothes the voltage, the inductance chops the current)</p></li></ul><p></p>
23
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<p>How is an synchronous buck converter built? How does the characteristics of the synchronous buck converter look like?</p>

How is an synchronous buck converter built? How does the characteristics of the synchronous buck converter look like?

  • Half-Bridge + Resistance + Inductance + Capacitor

  • Provides lower ON-resistance that the asynchronous embodiment

  • Very complicated phase portraits inbetween

24
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What are boost converters?

  • Power Electronics arrangements to ouput a voltage bigger than the input

  • As a mnemotic, switch, diode and inductance rotates one position counterclockwise to reach the boos configuration

<ul><li><p>Power Electronics arrangements to ouput a voltage bigger than the input</p></li><li><p>As a mnemotic, switch, diode and inductance rotates one position counterclockwise to reach the boos configuration</p></li></ul><p></p>
25
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<p>How is an asynchronous boost converter built? How does the characteristics of the asynchronous boost converter look like?</p>

How is an asynchronous boost converter built? How does the characteristics of the asynchronous boost converter look like?

  • Inductance + Switch + Diode + Capacitor + Resistance

  • Ripple seen in the current graph, kinks in the voltage corresponding to the discontinuities of the current ripple

<ul><li><p>Inductance + Switch + Diode + Capacitor + Resistance</p></li><li><p>Ripple seen in the current graph, kinks in the voltage corresponding to the discontinuities of the current ripple</p></li></ul><p></p>
26
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<p>How is a synchronous boost converter built? How does the characteristics of the synchronous boost converter look like?</p>

How is a synchronous boost converter built? How does the characteristics of the synchronous boost converter look like?

  • Inductance + Half-Bridge + Capacitor

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