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Smart Grids

Problems &

SolutionsWalid Issa

Exeter University

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Electrical Grid

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Electrical Grid

- Dependency on a high capacity fossil-fuel generators

- Increasing carbon emissions- Getting a large amount of power in one

place - Using a long transmission lines to deliver

power - Not economic - Has low reliability against sudden faults

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Microgrid

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Microgrid

- Integrate renewable resources- Control the flow of power- Reduce Carbone emissions- Reduce losses- Reliable against sudden faults

- Customer is a part of the grid

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GRID Micro-GRID

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Microgrid Modes

Grid-Connected mode

Island mode

Microgrid

Point of Common Coupling (PCC)

GRID

SWITCH

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Interfacing

Sources

Battery

Grid Loads

INVERTER

DC AC

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Inverter

DC-Link Capacitor

L1

C

L2

PWM Generator Vref

Voltage Controller

LCL Filter

Bidirectional DC/AC Converter (inverter)

SensorsACDC

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Uses DC Boost to step up the DC

voltage

Uses transformer to step up the AC

voltage

Uses transformer to step up the DC

voltage

Uses many PV to step up the DC

voltage

Inverter’s Topologies

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DSP ControllersTMS320F28XX

LEM Sensors1 mH

50 µF2000 µF

Inverter

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Electric Vehicle

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Active & ReactivePower Measurement

90º ¼ cycle ¼ T

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Sine wave PWM Generation

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Microgrid Literature

1- Voltage and Current Regulation

Goals: Low Distortion No Resonance Regulated Voltage Smooth Step Response

Proposed Solutions: PI, PID Controllers P+Resonant Controllers Adaptive Controllers Repetitive Controllers

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Microgrid Literature

2- Power Sharing

Goals: Adequate Power sharing Accurate Power control Without Communication if possible Smooth Step Response

Proposed Solutions: Master – Slave Controllers Current Chain Scheme

Droop Control

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Microgrid Literature

3- Power Sharing (‘Droop Control’)

Goals: Accurate Reactive Power control Small Frequency and voltage

deviations Harmonics Sharing Smooth Step Response

Proposed Solutions: PID Control Angle droop controller External supplementary loops

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Microgrid Literature

4- Islanding Detection

Goals: Detect the grid absence within 2

sec Proposed Solutions:

Passive Methods Voltage, Frequency, phase

deviations Active Methods

Positive Feedback, harmonic injection, …

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Microgrid Literature

5- Power Management and Central Control

Goals: A manager should decide the power

for each inverter Mode Controlling

Proposed Solutions: Hierarchical Control

Primary Control Secondary Control Tertiary Control

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Research Goals- Not concerned about energy sources- Not concerned about sources

fluctuations

BUT .. .. .

Circulation currents Power sharing in island mode Smooth Transition Microgrid stability

Paralleling Inverters operation in Island Mode

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Parallel Inverters

DC

DC

DC

AC

DC Link Capacitor

Bi-Directional DC/AC Converter

DC

DC

DC

AC

DC Link Capacitor

GridSTSPCC

Bi-Directional DC/AC Converter

UPS

Cenrtal Controller Unit Controller

Unit Controller

Slow

Communication

Stable & Fixed

Stable & Fixed

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Methodology

- Microgrid Modeling

- Proposing a controller

- MATLAB/SIMULINK

- Practical implementation

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So Far …

IGBT Block

Output Filter

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Voltage Sensor

Current Sensors

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IGBTs and Filters

Voltage and current sensors

Power supply

Interfacing and

switching boards

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dSpace Control

unit

Loads

Interfacing and monitoring platform

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Active resistive

load

Reactive inductive

load

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Interfacing Platform

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36.32 36.33 36.34 36.35 36.36 36.37

-30

-20

-10

0

10

20

30

10 15 20 25 30 35 40-20

-10

0

10

20

30

40

Time

Rea

ctiv

e P

ower

Inverter 1 Reactive power

Inverter 2 Reactive power

Output Voltage of both

invertersTHD = 1.8%

Results

Reactive Power

sharing

First controlle

r

Second controlle

r

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40 45 50 55 60 65 7030

40

50

60

70

80

90

100

110

Active Power

sharing

DC link voltage

response

Controller is enabled

40 45 50 55 60 65 70-20

-15

-10

-5

0

5

10

15

20

Time

Act

ive

Pow

er

Inverter 1

Inverter 2

Inverter 2

Inverter 1

Droop Control

DCk

-

--

PavgP

*P

DClinkV

*DClinkV

Threshold

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Keywords

- Droop control- Voltage & Current controllers- Reactive power sharing in island

mode- Islanding Detection - Supervisory Control- MPPT for solar inverters

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Projects Ideas- Sine wave PWM Generator- Inverter Voltage controller- Power Measurement- MPPT for solar inverters- Buck-Boost converter- Synchronization (Zero crossing

detection - PLL)- Droop Control for parallel

inverters- Smart Charger based on Droop

control- SCADA for microgrid (Labview)

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Useful Docs and REfs

Papers

Matlab Files

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Thank You …

https://www.facebook.com/pages/Walid-Issa/274572119317029