Copy7 of Liserre Keynote Speech Electrimacs - Prof. Dr ...

Prof. Marco Liserre, PhD, IEEE fellow

Head of the Chair of Power Electronics

Christian-Albrechts-University of Kiel

Kaiserstr. 2, D-24143 Kiel

[email protected]


From 1 kW to 10 MW: The race of Power Electronics to Conquer the Electric Grid

ICRERA 2013 – Keynote speech

Marco Liserre|[email protected]| slide 2 | 23.10.2013


Chair of Power Electronics

P

gI

VLV

E

Q

VSI

vCgL

e

gi

+

-

+

-

The synchronous machine has a central role in the centralized power system

The “synchronous converter” major player in the future power system

Interfacing power production, consumption, storage and transportation

within the future power system based on smart grids

Based on semiconductor technology and signal processing


The PWM grid converter, a kind of new synchronous machine ?




vCgL

e

gi

+

-

+

-

vCgL

e

gi

+

-

+

-

P

gI

VLV

E

Q

The PWM grid converter is equivalent to multiple synchronous

machines

The grid converter can control the active and reactive power flow in a

vast frequency range

P

gI

VLV

E

Q

P

gI

VLV

E

Q

1 h n

. . . .

vo

lta

ge

harmonic order

1

h n

PWM carrier and sideband

harmonics

The PWM grid converter frequency behavior





1. Introduction: from active rectifier to smart grid & renewables

2. Synchronization, harmonic control and resonance damping

3. A new role for the grid-converter: from “multifunctional” to

“universal” converter

4. The last challenge: reliability

5. What’s next ? The Smart Transformer

Outline





Introduction





medium and high power systems:

• multi-drive systems

• single drives working frequently in

regenerative operation like cranes and

elevators

PCCVLVGV

ACTIVE

RECTIFIER

p

load

load


Active rectifier




STATCOMPCCVLV

GV

q

Series and parallel active filters enhance grid power quality compensating

voltage sag, harmonic, reactive power, etc .


Power quality conditioners

AC

TIV

E

FIL

TE

R

load

AC

TIV

E

FIL

TE

R

load

LVGV




separate control loops active and reactive power

active power control

one station controls the active power

other station controls the DC-link voltage

reactive power control

reactive power or AC side voltage

HVDC based on

PWM grid

converter offers . .


HVDC




Grid

Phase A

Larm

Larm

#2

n

#1

#2

n

#1

Grid

Phase A

Larm

Larm

#2

n

#1

#2

n

#1Phase A

+Vd

c/2

Larm

Larm

Idc

-Vd

c/2

Vdc

#2

n

#1

#2

n

#1

V∑

C_u

pp

V∑

C_l

ow

S1

S2VC

Sub-module

in

idiff

ip

Vac

VSM

Grid

iac0

Phase B

Phase C

-2.0

0.0

2.0

kA

Ia... Ia... -1.5 Ib... Ic... -2 Ipa Ipb Ipc 1.5 2

-2.0

0.0

2.0

kA

Ia... Ia... -1.5 Ib... Ic... -2 Ipa Ipb Ipc 1.5 2

0

400

800

MW

P Qo P Pdc

-400

0

400

kV

Cc Bb Aa Vabc_t Vabc_g

kA

Simulation results

kA

MW MVAr

kV

P, Q

Arm currents

AC curents

AC voltage

Fault

Limitation

All major companies in the field

Unless properly controlled, the circulating

currents lead to increased losses, higher ratings

of the devices, and may lead to unbalances and

disturbances during transients.

Faults propagation is an issue !


MMC-HVDC




Source: IET, Aalborg University

Power Flow

Information Flow

Generators

TransmissionNetwork

DistributionNetwork

Customers

Distributed Generation

Green Power

Power Flow

Information Flow

Generators

TransmissionNetwork

DistributionNetwork

Customers

Generators

TransmissionNetwork

DistributionNetwork

Customers

Distributed GenerationDistributed Generation

Green Power

Main issues:

short and long-term expectancy and emergency loadings and reverse power flows in local grids

Hosting capacity of renewables and reliability of the grid


Scenario: smart grid and renewables




High efficiency (new topologies and new devices)

Transformer-less topologies and Central inverters

Extended lifetime

Reactive power injection (ancillary services)

Inverter market share


Power converters for photovoltaic systems




Best renewable source for integration in residential buildings

Single-stage transformerless achieves high efficiency

Interaction with the grid (anti-islanding, reactive power injection,

ancillary services)

Vdc

LCL

Filter

FilterDC/AC

Converter

Input power

sourcetransformer & utility

grid

local load

microgrid

PV

Panels

String

Vpv

Ipv

e

PWM

Anti-Islanding

Protections

i

Grid

Synchronization

MPPT Vdc

Control

AC Current

Control

AC Voltage

control for

ancillary functions


Small power (<5kW) PVS




grid frequency

switching frequency


Several new topologies

grid frequency

switching frequency

Vincotech patent: NPC inverter

with decoupled output and

Mosfet’s

S. V. Araùjo, P. Zacharias, R. Mallwitz,

“Highly efficient single-phase

transformerless inverters for grid-connected

photovoltaic systems”, IEEE Transactions on

Industrial Electronics, 57 (9), September

2010.




Power quality


Leakage current

Size of the filter

Comparison

Power converter rating




Transformerless inverter

topologiesEfficiency

Reactive

power

Grid

current

quality

Leakage

current

Size of

the filter

Power

Converter

Rating

PVS

Manufacturers

H5 + + ++ + + ++ SMA

HERIC ++ + + + - ++ Sunways

H6 + + ++ + + + Ingeteam

HB-Neutral Point Clamped ++ + + ++ ++ ++ Danfoss

FB-Zero Voltage Rectifier - + ++ + ++ - -

Araujo ++ - + - -- + -

NPC with decoupled output ++ + - ++ - - -

How the new topologies compare with those on the market ?

Problems arises in the size of the filter, power converter rating and power quality !


Comparison




Reliability

10-20 MW wind turbines (power converter topologies and generators)

Paralleling of power converters or MV solutions ?

Gearbox

Converter

module 1

Converter

module 2

Converter

module 3

Converter

module 4

Converter

module 5

Converter

module 6

LV/MV

Transformer

Generator


Power converters for wind systems




Best choice immediately outside residential areas for low impact on

the landscape

High penetration in stand-alone also in combination with other

DER

Power limitation issues, weak grid connection


Medium power (<200kW) WTS




0 0.05 0.1 0.15 0.2600

650

700

750

time [s]

roto

r spe

ed

[rp

m]

estimated rotor speed

rotor speed


Wind turbine systems: small/medium power (<200kW) WTS




AC/DC DC/AC

GENERATORE

RETE

ELETTRICA

DSP

Interf

DSP1

LCL

filter

misura

tensione

misura

corrente

MOTORE DI

IMBARDATA

TURBINASKIIP 132GDL120-4DU

misura

tensionemisura

corrente

DSP

Interf

DSP 2

SKIIP 132GD120-3DU

misura

tensione

IRAMS10UP60B

misura

tensione

Interf

chopper

Interf

inverter

Interf

raddrizzatore


Wind turbine systems: small/medium power (<200kW) WTS




Synchronization,

harmonic control

and resonance damping





v

kv v

qv

SOGI-QSG

qv

/ dq

PI

v

SRF-PLL

ff

qv

dv

2 2( ) ( )

v k sD s s

v s k s

Synchronization will be crucial for all the grid connected inverters to adapt their behavior in any grid condition

Single PLL based on a second order integrator acting as a sinusoidal follower is the building block of a class of advanced synchronization methods


Synchronization: SOGI-PLL




v

kv v

qv

SOGI-QSG

qv

/ dq

PI

v

SRF-PLL

ff

qv

dv


The origin of SOGI-PLL




v

vv

v

qv

v

qv

v

v

v

v

12

12

DSOGI

PNSC

v

v

SOGI-QSG()

e

qv’

v’

w’

v

e

qv’

v’

w’

v

SOGI-QSG()

PI

[Tdq]

qv

dv

v

SRF-PLL ff

2 2

q d qv v v

2

2 22

o

o os s

qv

Detection of the positive and negative sequences will be important during grid-faults

Three-phase system synchronization needs a vectorial approach and a dual PLL


Double-SOGI to handle inverse sequence




Re 2 2( )P s p i

sC s k k s

s

2 2

3,5,7

( )( )

ih

h

ss k

s h

• Resonant control

• Repetitive control based on DFT 1

0

2 2cos

h

N i

DFT ai k NF z h i N z

N N

1iPResC

resonant controller

i

iG

e

pG*i

i

i

i

iG

e

pG*i i 'i

cG

DFTF FIRk hi

RepF z


Harmonic Controllers




Hybrid solution: generalized integrator in dq frame


Harmonic Controllers




Higher power DPGS (like MW WT-systems) switch at low frequency and

resonance frequency needs to be damped selectively

Virtual Losses Harmonic Spectrum


Passive damping: selective damping




vi

( )dG s ( )fG s( )PIG si

controller

with active

damping

plant

( )ADG s


Active damping by means of Notch filter

Converter current

FFT

Self-commissioning




A new role

for the grid-converter






System level challenges

Photovoltaic panels

Wind turbines

Battery banks

Static Switch

Grid

Nonlinear loads

Linear loads

0 0.005 0.01 0.015 0.02-4

-2

0

2

4

0 0.005 0.01 0.015 0.02-1.5

-1

-0.5

0

0.5

1

1.5

0 0.005 0.01 0.015 0.02-1.5

-1

-0.5

0

0.5

1

1.5

0 0.005 0.01 0.015 0.02-1.5

-1

-0.5

0

0.5

1

1.5

0 0.005 0.01 0.015 0.02-1.5

-1

-0.5

0

0.5

1

1.5

0 0.005 0.01 0.015 0.02-1.5

-1

-0.5

0

0.5

1

1.5

0 0.005 0.01 0.015 0.02-1.5

-1

-0.5

0

0.5

1

1.5

Open points mainly at system level (harmonics

and resonance propagation and damping)




Results: load support in case of a voltage sag of 0.15 p.u.

Grid voltage E (top): voltage dip of 0.15 p.u., load voltage Vload (middle ), grid current Ig (bottom)


Voltage support provided by the DPGS at load level

The grid converter can also maintain the voltage level on a load




The reactive power injection by grid-connected systems can enhance the voltage

profile

AC DC

PQ-inverter control

Optimal Reactive Power Control Dynamic

Load-Flow Reduced Network Model

QPV (t)

Distribution Network

MV/LV

PTR (t) VTR(t) θTR(t)

PPV (t) QPV (t) VPV(t) θPV(t)

NON-OPTIMIZED

CONDITION

(PV INVERTER OFF)

OPTIMIZED CONDITION

(PV INVERTER ON)

TRANSFORME

R

SUBSTATION

PCC TRANSFORME

R SUBSTATION PCC

F [HZ] 50 50 50 50

V1 [V] 229 228 230 229

V2 [V] 228 226 228 228

V3 [V] 228 230 228 231

I1 [A] 52.5 1.1 33 3.2

I2 [A] 52 1.1 36.5 2.2

I3 [A] 44 1.1 36.5 0.9

PTOT [W] 19950 730 20200 380

QTOT[VAR] 26550 0 8050 16500

cosφ 0.66 1 0.93 0.02


Voltage support provided by the DPGS at EPS area




PMSG

chopR

DCu

DCC

Machine-side

converter

Grid-side

converterS

i

Power

filter

1i 2

i

Machine-side

control

Grid-side

controlUnidirectional

Communication

Link

PCCe

State

Load

UWT1

STS

l 1Z liZ

UWTi UWTN

lNZ

Grid

gZ

PCCe

Circuit

BreakerG

e

State manager

PCCe

State

Unidirectional

Communication

Link

DG

units

State

ISLe


Universal inverter

The next step is a grid-converter that can work in any condition (grid-connection,

island)




Tra

nsfo

rma

ntio

n

ma

trix

TD

ST z

z 1

F z

F z

Pfk

PVk

V

GQ

GQ

GQ

GFQ

GFP

GP

GP

GP

GP

GQ

d

C

d

CV

V

S

S

z 1

T zDfk

ST z

z 1IVk

S

PCC

PCCE

S

S

S

S

PCCE

ST z

z 1PCC

S

PCC

(A)

(B)

(C)

(D)

baseV

base

PLANT


Universal Power control

The challenge is to use the same control structure for the different operation modes




;

101

102

103

-5

-2.5

0

2.5

5

Frequency (Hz)

Magnitude of the Sensitivity Transfer Function S(Z) (d)

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

1 5 10 50 100-30

-20

-10

0

10

20

Frequency (Hz)

a) |Z0| (d)

1 5 10 50 100

-300

-200

-100

0

Frequency (Hz)

b) Angle of Z0 (º deg)

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

0 0.2 0.4 0.6 0.8 1

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Imag

inar

y ax

is

Real axis

24kW

24kW

6kW

6kW

24kW

24kW

6kW6kW

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

d1

d2

d3

d4

d5

Re[L(z)]

Im[L

(z)]

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

Grid-connected

Island mode


Universal Power control




The kinetic storage of the UWT together with a suitable control strategy can be used to operate the UWT in island mode for a certain time without any additional storage

Statistical assessment of the power reliability improvement shall be done by means of SIER

Wind

turbineRotor

DC-link

capacitors

Aerodynamic

losses

Mechanical

losses

Generator

and switching

losses

Switching and

filter losses

Injected

power

Generated

powerWind

Power

Kinetic stored

energy

MPPT LOSSES

LOADb )

)

P

a P P

WT MPPT

WTb

) P P

) P

a

WT LOAD LOSSESb )

a )

P ( P P )

0

a )Grid connec

b ) Is

te

d

d

lan

Chopper

losses

0 10 20 30 40 500

5

10

15

20

Power (kW)

Pro

bab

ilit

y (%

)

Generation

Load P1

=15 kW

Load P2

=20 kW

Load P3

=25 kW

Load P4

=30 kW

Load P5

=35 kW

Load P6

=40 kW


Universal operation without storage




UWT can be used to reduce the average interruption time

The reduction in the average interruption time obtained by means of the Universal Operation is quite remarkable, being at least 22.27 % and 60.5 % in the best case

'Tμ (s)

Average Load Consumption

P1μ P2μ P3μ P4μ P5μ P6μ

Avera

ge

Inte

rru

pti

on

Du

rati

on

T 1μ 3.95 4.64 5.26 5.69 6.19 6.52

T 2μ 62.50 71-02 78.32 83.37 87.82 91.59

T 3μ 321.83 364.82 401.08 427.83 446.63 466.39


Calculation of reduction of interruption time




The last challenge





Common failure locations of power module packaging


Reliability




The killer is the temperature swing because of different thermal

coefficients

T1

D1

T2

D2

T3

D3

T4

D4

D5

D6

Time(s)

Ju

nctio

n te

mp

era

ture

(℃

)

Dnpc

T1

T2 D1

D2

Time (s)

Temperature vs reliability





Thermal stress is determined by many factors & time constants.

Mechanical ElectricalEnvironmental

sec

Medium term

(Mechanical control)

Long term

(Ambient change)

Short term

(Converter control)

houryear millisec

1 year, 3 hours step 3 hours, 1 second step 0.2 second, 0. 01 millsec step


Thermal stress of IGBT in wind power converter




Co

nsu

me

d B

10

life

tim

e (

%)

Wind speed (m/s)C

on

su

me

d B

10

life

tim

e (

%)

Consumed life time vs. different wind speeds.

Consumed life time vs. different failure mechanisms.


Lifetime of IGBT by medium term thermal loading




0

25

75

90

100

150 500 750 1000 1500

Voltage(%)

Time (ms)

DenmarkSpain

Germany

US

Keep connected

above the curves

Grid voltage dips vs. Withstand time

100%

Iq /Irated

Vg (p.u.)

0.5

0

Dead band

0.9 1.0

20%

Reactive current vs. Grid voltage dips

Withstand extreme grid voltage dips

Contribute to grid recovery by injecting reactive Iq. (up to 100% capacity)

Higher challenges for the wind turbine system


Low Voltage Ride Through challenges reliability




0

500

1000

1500

2000

2500

3000

3500

4000

4500

Tout Dout Tin Din Dnpc

Normal

phase B

phase A

phase C

Lo

ss (

W)

0

500

1000

1500

2000

2500

3000

3500

4000

4500


Normal

phase C

phase A

phase B

Lo

ss (

W)

0

500

1000

1500

2000

2500

3000

3500

4000

4500


Normal

phase A

phase B

phase C

Lo

ss (

W)

1 phase grounded 2 phase connected

3 phase grounded

(D1=0 p.u., vw=12 m/s, no negative seq. I, 110 % DC bus)

LVRT operations impose the diodes and inner switches with significant larger losses than the most stressed normal operation.

Loss distribution among the three phases is asymmetrical under the unbalance faults.


Loss distribution




Different sensors can be employed:

ambient sensors (temperature, humidity and pollution);

internal sensors (module temperature, vibration, electric parameters)

Data acquisition is very important: there are issues related to the amount of data that is possible to store and how to use those data.

Two main goals: a proactive maintenance plan or proactive control schemes

Wind power converters under operation

Wind speed

Sensors

Temperature

Sensors

Humidity

Sensors

Voltage

Sensor

s

Current

Sensors

Vibration

Sensors

Wireless Wiredor

Communication

Co

ntr

ol

On-line remaining life

prediction

Condition monitoring

Failure cause and location

analysis

Proactive control scheme

Workstation


Real time monitoring




The reactive power changes the losses distribution among the power devices hence can be used to control the thermal cycling and the peak temperature of some of them

Many new WTS topologies are based on a modular design that allows circulating reactive power among them

...

...Multi winding

generator

To grid

AC

DC

DC

AC

AC

DC

DC

AC

...


Active Thermal control by means of reactive power




Generator

AC

DC

DC

ACFilter FilterGear

Full scale converter

PV PV PV PV PV

Capacitor for Local

Reactive Power

Compensation STS

1000kVA

20kV

Grid

0.4kV

1 2 3 4 n

In a park either a wind one or a photovoltaic one, it is possible to circulate the reactive power among the power converters

An optimization procedure can be carried out to select minimum reactive power circulation (or minimum losses) versus minimum thermal excursion


Active Thermal control by means of reactive power




Reactive power (p.u.)

Ph

ase

cu

rre

nt a

mp

litu

de

Ig

(p.u

.)

8 m/s

10 m/s

12 m/s

Underexcited Overexcited

Reactive power (p.u.)

Ph

ase

an

gle

Ig

- U

c (

de

gre

e)

8 m/s

10 m/s

12 m/s

Underexcited Overexcited

Current amplitude Ig vs. reactive power Q

Phase angle α vs. reactive power Q

0

1000

2000

3000

4000

5000

T1 D1 T2 D2 Dnpc

Q- max

No Q

Q+ max

Lo

ss (

W)

Loss distribution of 3-NPC inverter with different extreme Q (10m/s, P=6.3 MW)

The reactive power increases the losses, but the loss distribution is modified


Modified loss distribution by reactive current in WTS




Wind gust from 10 m/s to 8m/s then to16 m/s in 10 seconds

Junction temperature in clamping diode Dnpc fluctuates up to 43K

Large ΔTj results in reduced life time of devices

Cu

rre

nt re

fere

nce

s (

A)

Active current IP

Reactive current IQ

Time (s)

Win

d s

pe

ed

(m

/s)

Ju

nctio

n te

mp

era

ture

(℃

)

T1

T2 D1

D2

Time (s)

Dnpc43 K

Thermal cycling of 3L-NPC inverter Wind gust and current references

Prated=10 MW, Vll=3.3 kV, fs=800 Hz


Thermal cycling during a wind gust




The idea: since the temperature fluctuation is the most dangerous for reliability, during rough wind condition the reactive power can be used to warm-up the most –stressed device. When the wind gust hits the WTS, reactive power is imposed to zero

Thermal cycling of 3L-NPC inverter Wind gust and current references

Prated=10 MW, Vll=3.3 kV, fs=800 Hz

Cu

rre

nt re

fere

nce

s (

A)

Active current IP

Reactive current IQ

Time (s)

Win

d s

pe

ed

(m

/s)

Ju

nctio

n te

mp

era

ture

(℃

)

T1

T2

D1

D2

Time (s)

Dnpc 24 K


Reducing thermal cycling using reactive power




Q is circulated among paralleled converters

Larger Q range can be achieved

Grid codes can be still satisfied

T1

Dnpc1

D1

T2

D2 Grid

Converter 2 (Overexcited operation)

...

Converter N

P1

P2

Underexcited

-Q

Dnpc2

T3

D3

D4T4

Overexcited

+Q

Converter 1 (Underexcited operation)

T1

Dnpc1

D1

T2

D2

Grid

Converter 2 (Overexcited operation)

...

Converter N

P1

P2

-Q

Dnpc2

T3

D3

D4T4

+Q

Converter 1 (Underexcited operation)

Parallel converters in single wind turbine system Parallel converters in wind park


Idea to extend to Q range




Cu

rre

nt re

fere

nce

s (

A)

Active current IP

Reactive current IQ

Time (s)

Win

d s

pe

ed

(m

/s)

Cu

rre

nt re

fere

nce

s (

A)

Active current IP

Reactive current IQ

Time (s)

Win

d s

pe

ed

(m

/s)

Cu

rre

nt re

fere

nce

s (

A)

Active current IP

Reactive current IQ

Time (s)

Win

d s

pe

ed

(m

/s)

Ju

nctio

n te

mp

era

ture

(℃

)

T1

T2 D1

D2

Time (s)

Dnpc43 K

Ju

nctio

n te

mp

era

ture

(℃

)

T1

T2

D1

D2

Time (s)

Dnpc 24 K

Ju

nctio

n te

mp

era

ture

(℃

)

T1

T2

D1

D2

Time (s)

Dnpc

39 K

Without reactive power With underexcited reactive power With overexcited reactive power

Thermal fluctuation during wind gust can be improved

Thermal fluctuation in compensating converter are not significantly enlarge


Parallel operation of WTS




What’s next ?






Critical issues of the future electric grid





A possible solution: the Smart Transformer




- Power quality enhancement: disturbance isolation, harmonics and transients

- DC-connectivity: future MVDC, low voltage DC grids and renewable

energy

- Fault reclosing coordination

- Energy storage: Electric vehicle batteries (challenges and opportunities)


Capabilities of the Smart Transformer




One stage (AC-MV/AC-LV)/ Two stage (AC-MV/DC-MV /AC-LV)

Reduced component counts

Does not allow integration of either MV/LV DC network

disturbances on one side may also affect the other side

Three Stage (AC-MV/DC-MV/DC-LV/AC-LV)

DC-links on both sides and performing three stages of conversion

Allows direct integration of renewable DC sources

Modularity


ST Architecture





Several architectures

1

2

4

3

5




- Cascaded H-bridge seems to be the best solution but it does not allow MVDC connectivity

- MVDC connectivity is at the expense of efficiency


Comparison




Power electronics converters connected to the grid have unexplored opportunities (e.g. multifrequencies)

Many applications such as PVS, WTS or HVDC still have had recent innovation both in the adopted power converter topologies and their control

Harmonic/resonance propagation/damping at system level and universal operation are still open points

Design and Control for reliability of power electronics systems is important for the electric grid

The Smart Transformer is the next big thing !


Conclusions




The work on power converter and the grid has been developed in the last 13 years within or in cooperation with

Politecnico di Bari (Italy)

Aalborg University (Denmark)

Alcalá University (Spain)


Acknowledgement

Copy7 of Liserre Keynote Speech Electrimacs - Prof. Dr ...

Documents

Transcript of Copy7 of Liserre Keynote Speech Electrimacs - Prof. Dr ...