EE464-Static Power Conversion-II

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# EE-464 STATIC POWER CONVERSION-II

# Multi Level Inverters

## Ozan Keysan

## [keysan.me](http://keysan.me)

### Office: C-113 <span class="meta">•</span> Tel: 210 7586

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# Switch Utilization in 3-Ph Inverters

## Assuming pure sine output (i.e. large enough inductance)

## Transistor voltage and currents

## \\(V\_T = V\_{d,max}\\)

## \\(I\_T = \sqrt{2} I\_{o,max}\\)

# Switch Utilization in 3-Ph Inverters

## Output Power

## \\(S\_{3-ph} = \sqrt{3} V\_{l-l} I\_{o,max}\\)

## There are 6 switches, so:

### Switch Utilization=

\\(= \dfrac{\sqrt{3} V\_{l-l} I\_{o,max}}{6 V\_{d,max}  \sqrt{2} I\_{o,max}}\\)

# Switch Utilization in 3-Ph Inverters

## Linear Mode

## \\(= \dfrac{1}{2 \sqrt{6}}  \dfrac{\sqrt{3}}{2 \sqrt{2}} m_a\\)

\\(= \dfrac{1}{8} m_a\\)

## Same utilization factor, in other words 3-ph inverters use 50% more switch to deliver 50% more power!
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# Effect of Blanking (Dead) Time

### There has to be off time between swithcing instants to present short circuit of Vd (can be up to \\(2-3 \mu s\\))

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# Effect of Blanking (Dead) Time

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# Effect of Blanking (Dead) Time

## Results in non-linearity in the voltage output

### [Reading assignment for curious students](https://ieeexplore.ieee.org/abstract/document/9102428)

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# Effect of Blanking (Dead) Time
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## \\( | \Delta V\_o | =  \dfrac{2 t\_{\Delta}}{T\_s} V\_d\\)

### Always reduce the output voltage magnitude wrt. current direction

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# Effect of Blanking (Dead) Time

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# Multi-Level Inverters
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- ### Used commonly in high power (MW, kV) converters
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- ### Increases output voltage capacity
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- ### Minimizes THD even with low switching frequencies
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- ### Reduce EMI due to lower voltage steps

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# Two-Level Inverter Waveform

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# Multi-Level Inverter Waveforms

### Three level, 
### Five Level,
### and Seven Level voltage Output Waveforms

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# H-Bridge Inverters

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# H-Bridge Inverters

### Three Level (unipolar) PWM Output

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## H-Bridges can be connected in series for higher voltages

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## What are the voltage levels?
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: 2Vdc, Vdc, 0, -Vdc, -2Vdc

### Specific harmonics can be elimination by proper \\(\alpha\_1, \alpha\_2\\)

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# Five-Series Cascaded H-Bridge Inverters

### How many voltage levels?

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# 11-Level Cascaded H-Bridge Inverters

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## 11-Level Cascaded with Five Separate Sources

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- ### Diode-clamped (a.k.a. neutral-clamped)
- ### Capacitor-clamped (a.k.a. flying-capacitors)
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# Multi-level Inverter Topologies

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# Diode Clamped Multi-level Inverters

### Five-level diode clamped inverter (Neutral Point Clamped (NPC))
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## Five-level diode clamped inverter

## Voltage Levels: Vdc

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## Five voltage-level diode clamped inverter

## Voltage Levels: 0

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## Five voltage-level diode clamped inverter

## Voltage Levels: Vdc/2

<img src="./images/ee464/diode_clamped_multilevel_3.png" alt="Drawing" style="width:350px;">
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## Even Higher Voltage Levels
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### 3 voltage sources cascaded

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## Even Higher Voltage Levels

### 5-Photovoltaic panels connected in series

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## Even Higher Voltage Levels

## Switching States: Can you find the pattern?
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### A set of five switches is on at any time

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## Even Higher Voltage Levels

## Line-to-line voltage

<img src="./images/ee464/6level_diode_clamped3.png" alt="Drawing" style="width:800px;">
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## Alternate PWM Techniques

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# N-Level Cascaded H-Bridge Inverters

## Five-level Output Voltage Waveform (fc=3kHz)

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# Multi-Level SVPWM

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# Multi-level SVPWM

## 3-Level

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# Multi-level SVPWM

## 5-Level

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# Multi-level SVPWM

## Voltage Vectors of a 6-Level Inverter

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# Further Reading

- ### [Multilevel Inverter – Types & Advantages](https://www.elprocus.com/multilevel-inverter-types-advantages/)
- ### [Introduction to MultiLevel Inverters](https://docplayer.net/34231342-Introduction-to-multilevel-inverters-rijil-ramchand-associate-professor-nit-calicut.html)
- ### [Multilevel Inverters](http://shodhganga.inflibnet.ac.in/bitstream/10603/16448/7/07_chapter%202.pdf)
- ### [Multilevel Inverters: A Survey of Topologies, Controls, and Applications](https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1021296)
- ### [Multilevel Power Converters ](https://pdfs.semanticscholar.org/049a/a38514290aa78070abe1cd03a8b4a66edd73.pdf)

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## You can download this presentation from: [keysan.me/ee464](http://keysan.me/ee464)