chair of power electronics

Chair of Power Electronics | Marco Liserre| [email protected] slide 0

- Associate Prof. at Politecnico di Bari, Italy

- Professor – Reliable Power Electronics at Aalborg University, Denmark

- Professor and Head of Power Electronics Chair at Christian-

Albrechts-Universität zu Kiel, September 2013

Listed in ISI-Thomson report World’s Most Influential Minds

Active in international scientific organization

(IEEE Fellow, journals, Vice-President, conferences organization)

EU ERC Consolidator Grant (only one in EU in the field of power sys.)

Created or contributed to the creation of several scientific laboratories

Grid-connected converters (15 years) and reliability (last 5 years)

Chair of Power Electronics

Head of the Chair


Staff


Professors2

Secretaries &

Technicians3

Graduate Research Assistants

17Scientific Guests/ye

artyp. 1 - 3

Student Research Assistants

10

Master's and

Bachelor's theses/ye

arca. 10

Third part funding (2013-2015)

MV Grid Analysis(BMWI, 2015-

2018)2.320.000 €

HEART(EU, 2014-2019)

1.800.000 €

PE Region(EU)

1.049.963 €

Mediumvoltage laboratory and

instruments (SH, DFG, EKSH,

CAU)1.522.340 €

LIFE-Wind(EKSH, 2015-

2016)150.000 €

Active Thermal Control

(EKSH, 2015-2018)

55.000 €

2 Von Humboldt Fellowship

(2014-2016)140.000 €

Reliability Issues in PE

(ECPE)12.500 €

Teaching(CAU, 2015-

2016)10.000 €


Power system and Thermal managment

RTDS System

Rack 1 Rack 2Synchronization

and Communication

System

Analogue

Input \ OutputDigital

Input \ Output

Power

Amplifier

Power-

Hardware-

In-Loop

MV/LV

Grid

Hardware-

In-Loop

Complex

Real Time

Algorithm


Medium Voltage Laboratory

Geplante Baumaßnahmen in Gebäude B

(Stand Oktober 2015).

Geplante Tests im Mittelspannungslabor.


Sm

art

Tra

nsfo

rme

r


Christian-Albrechts-Universität zu Kiel

Kaiserstraße 2

24143 Kiel

Smart Transformers: System-Level Challenges

Marco Liserre, Giampaolo Buticchi, Markus Andresen, Giovanni De Carne, Levy Costa


Outline

From the Solid-State-Trasformer (SST) to the Smart

Transformer

Smart Transformer impact on the eletric grid

The challenges that the system poses to the component


Concept and Definition of SST

Definition

• by Mr. McMurray, 1968 : Electronic Transformer is a device based on solid state switches which

behaves in the same manner as a conventional power transformer.

• by Mr. Brooker, 1980 : Solid State Transformer is a apparatus for providing the voltage transformation

functions of a conventional electrical power transformer with waveform conditioning capability.

• Currently: Power electronic based solution to replace the standard LF transformer, with the features:

– galvanic isolation between the input and the output of the converter.

– active control of power flow in both directions

– compensation to disturbances in the power grid, such as variations of input voltage, short-term sag or swell.

– provide ports or interfaces to connect distributed power generators or energy storage device

• Smart Transformer: Solid State Transformer with control functionalities and communication.


Traction application

Main concern:

• Reduce volume and weight (increase power

density)

• Efficiency improvement

Traditional solution

• LF transformer (16 2/3 Hz) – very bulky and heavy

• Low efficiency: 90 ~ 92 %

• Around 7tons


Distribution application

Main requirements

• Replace the traditional LF distribution

tranformer

• HF/MF isolation

• Provide additional functionalities

Functionalities

• Voltage sag and harmonics

compensation

• Load voltage regulation

• Disturbance Rejection

• Power Factor Correction

• VAR Compensation and Active

filtering

• Overload and short-circuit

protection

(available dc-link)


The Smart Transformer

The Smart Transformer is:

a solid-state transformer

a power system management node

a link to different ac or dc infrastructures

a link to other energy sources (gas, heat, hydrogen)

a support for the EV infrastructure


The Smart Transformer

The Smart Transformer features shall be:

LV and MV DC-links available

Advanced control of all the three-stages

The system should be able to work even with faulty modules

During partial loading conditions it should be able to fully use its rating for other services


Load parameter identification with respect

to Voltage and Frequency

Load identification


Measured resonance due a PV-plant

Impedance identification

Multiple resonance peaks due to several connected inverters


Storage integration

Intermittent nature of Renewable Energy System and

EV charging stations

Fast Voltage Variation due to faults in MV grid


DG impacts on LV voltage profilesminimized by voltage regulation

Reactive power injection and voltage control

Reduction of losses in MV grid, Black-start funtionality, sustain otherdistribution feeders in case of faults

ST can block the reverse power flow in the MV-line



LV-grid Static test(hosting capacity)

LV-grid Dynamic Test(load step change)

MV-grid Dual grid(fault test)



OLTC TT+STATCOM Smart Transformer


Power quality

MV currents

LV Voltage

UnbalanceST

Harmonics control

-80

-40

0

40

80

-80

-40

0

40

80

Unbalanced distorted MV grid currents in conventional scheme

Curren

ts (A

)

Curren

ts (A

)

Balanced sinusoidal MV grid currents in proposed scheme

Multifrequency power transfer

Microgrid

Smart

Transformer

direct path at 150 Hz

Residential

Loads

Industrial

Loads

Current

Source

Current/Voltage

Source

Solar power

plants,

wind power

plants,

electric vehicles,

battery storages,

active loads

Solar power

plants,

wind power

plants,

electric vehicles,

battery storages,

active loads

Main Grid


Faults handling and islanding

Fault current limiting Allowing a controlled island


Resonance damping

Possible

resonance

Multiple resonance peaks can be damped with a system which works as active damper


Overload Control

Hard Limit

Voltage control

Frequency Control


Challenges

low-gain (m-grid)

medium/low efficiency

medium/low reliability

medium-gain (storage)

medium/high efficiency

high reliability

high-gain (reactive power)

high efficiency

medium/high reliability

replaces dispersed power

electronics solutions (STATCOM,

DVR, etc)

Higher hosting capacity of

DG and EV

Fault isolation and limitation

Embedding storage and

allowing and managing dc

connectivity


Challenges: modularity as a solution

A modular solution allow:

A 1 pu Smart Transformer makes no sense !

Expanding the

reactive power of

the MV converter

capability

ST-assisted m-

grid which could

become often

independent

It can work as a

weak connected

MV/LV system


Facing the challenges: efficiency

Voltage sharing Current sharing

constant ac voltage Uconstant ac current I

constant modulation index m

Module

s on/o

ff

Variable

sharing

Module

s on/o

ff

Variable

sharing


Current sharing

Efficiency curve for converters with similar power realized with different components: (a) not interleaved (for constant switching frequency),(b) interleaved (for constant current ripple by reduction

of switching frequency).

(a) (b)


Voltage sharing

Efficiency curve for converters with similar power realized with different components and constant current and modulation index: (a) for constant switching frequency, (b) for constant output current ripple.

(a) (b)


2 Level

VSI

MV AC

LV AC

QAB

QAB

QAB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

HB

QAB

MV

dc-link

LV

dc-link

UVW

U1

V1

W1

MV DC

LV DC

Junction temperatures, thermal cycles andaccumulated damage of T1 in the MMC.

Junction temperatures, thermal cycles andaccumulated damage of T4 in the QAB.

Normalized damage High load

profile

MMC (Transistor) 0.56

MMC (Diode) 0.24

QAB (Transistor) 0.03

QAB (Diode) 0

2 level VSI (Transistor) 1

2 level VSI (Diode) 0.1

Facing the challenges: reliability

Mission profile tests of an ST in thedistribution system:- Simulation of different profiles

(high/medium/low)- Evaluation of the the thermal stress for

the power semiconductors in all stages

Junction temperatures, thermal cycles andaccumulated damage of T4 in the QAB.

Investigated ST topology consiting of MMC, QAB and 2 level converter.


Thermal stress of the parallel modules

Influence of the number of activated parallel modules on the junction temperature in dependence of the load

current (without Arrhenius term).

How is reliability affected for load sharing with interleaved operation?

Influence of the number of activated parallel modules on the junction temperature in dependence of the load

current.


Activation/deactivation of modules

Efficiency based module activation

Activation of modules as the power increases


Summary

• Difference between SST and ST is in functionalities

• Identification/services/protection

• Design key: not a 1 pu System + modularity

• Modular system alternatives: energy routing or activating/deactivating modules

chair of power electronics

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