Power Electronics in New and Renewable Energy Systems

Mohammad A. Abusara Lecturer in control and Power ElectronicsRenewable Energy Research GroupCollege of Engineering, Mathematics, and Physical Sciences

Outline

Microgrid

Grid Connected Interleaved Inverter

Exhaust Heat Energy Recovery Systems

Marine Renewable Energy

Microgrid System

Microgrid System

Transformer

Critical loads

Non-critical loads

Main switch

SwitchDG

Grid

Buck IGBT

Boost IGBT

Buck mode

Boost mode

Bidirectional DC/DC converterDclink

Boost IGBT

35kWHr lithium-ion batteries (60kVA Inverter)

100kW micro Gas Turbine

MicroGrid: Controller Structure

Droop Controller

Voltage Controller

Battery Management

Power Measurement

Virtual L

Buck IGBT

Boost IGBT

Buck mode

Boost mode

Bidirectional DC/DC converter

Dc-Link Voltage

Controller

P

* 0P

* 0P

*P

nP

nQ

*Q

Charging

Discharging

Grid

Island

++ +

--

- refV

Q

*dclinkV

dclinkV

Charging/Dischaging

Grid/Island

Microgrid Challenges and Features

Challenges• Maintain stability during connection, disconnection, load application/shedding

• Good Load sharing in island mode

• Good current quality in grid-connected mode

Features• Seamless transfer from grid-connected mode to island mode and vice versa

• Improved current quality

• Improved transient response

Microgrid-Practical Test

Battery

Power Electronics

Microgrid-Practical Results

Transformer

Critical loads

Non-critical loads

Main switch

SwitchDG

Grid

Microgrid-Practical Results

The effect of virtual impedance on improving current THD

Grid Connected Interleaved Inverter

Interleaved Concept

One channel is replaced by a number of channels connected in parallel

Switching instants are phase shifted equally over a switching period

Introduced for telecommunication power supplies (low voltage high current)

Interleaved Inverter- Advantages

Smaller Power Switches

Smaller capacitors

Smaller Inductor

Novel DC/AC Grid Connected Interleaved Inverter

LuL

C

auV

cuV

buV

R

uL

uL

C

R

C

R

LI

L

L

dcV

1LI

OutIGV

1inVAdvantages over 2-level topology

Smaller C and hence so high output impedance to voltage harmonics (better current THD)

No need for a second L

Smaller in size

Controller Structure

)(zK

sL1

*1L

I

1LI

*2LI

CsRCs 1

sLu

1

uV

OutIcV

cV

LI

fV

PWM 1inV

1ModV

Controller

ZOH

ZOH sTde

2ModV

NModVNin

V

)( zK

cVfV

PWM

ZOH sTde

2LI

*NL

I

cV

PWM

ZOH sTde

NLI

sL1

sL11

N

2inV

)( zK

*OutI

fV

System Modelling

ZOH )( zK

*xLI

sTde

LI

)(sB

NxLI

uV

xinV

)(sA

( )fV z

2

3 21

( )( ) ( )u

u u u

L Cs RCsA s

LL Cs RC L NL s L NL s

1( ) ( )s

d

T sT seG z Z e A s

s

Passive Damping

• For active damping

• Sampling frequency (35kHz) is only 1.47 to 3.2 times the natural resonance frequency

• Passive damping is possible (small capacitor current thanks to interleaved topology)

ds ff 8

Passive Damping R

Root locus, R = 0 ohm -1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

-1.5 -1 -0.5 0 0.5 1 1.5

20uL H

Root locus, R = 0.5 ohm

The varying parameter in the Root Locus is the grid impedance

Controller Design

Frequency (Hz)

uLIncreasing

uLIncreasing

Unstable or critically stable

Frequency (Hz)

uLIncreasing

Stable

uLIncreasing

0.5 0.35( ) 100.97

zK zz

Phase Lag Controller

Proportional ControllerK(z) =10

Robust Digital Controller

Immunity to Grid Impedance VariationsExcellent Current Quality (THD=2.3%)

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

-1.5 -1 -0.5 0 0.5 1 1.5

1000uL H

Interleaved Grid Connected Inverter

Exhaust Heat Energy Recovery Systems

Energy Recovery SystemAlthough it is a dominantprime mover and one of themost efficient powersources, a typical modernturbocharged Diesel enginestill wastes significantamounts of fuel energy.

The exhaust waste heat energy can be recovered and converted into useful electrical power

Components of Exhaust Recovery System

• Fuel Saving 5-7%• Power Boost 10-15%

Turbine + High speed alternator Power Electronics

Exhaust Energy Recovery

Organic Rankin Cycle (ORC) System

ORC System Diagram

ORC Optimisation

CustomersOn road trucks Off road vehicle Stationary power plants

Hybrid Turbocharger

Power Electronics

TurbineCompPM Machine+

-

Motoring

Generating

Controlled DC

Marine Renewable Energy

Marine Renewable Energy Systems

Wave Tide

Thank You