smart transformers: which impact of the sic technology

Chair of Power ElectronicsChristian-Albrechts-Universität zu KielKaiserstraße 224143 Kiel

Smart Transformers: which impact of the SiC technology ?

Prof. Marco Liserre

Chair of Power Electronics | Marco Liserre| [email protected] slide 1

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.


Impact of the „Smart“ Transformer

Wind/PV systemsHarbours Charging stations Data centers

Line

mile

s

70´s

centralized peak

decentralized peak

massive investments to modernize the electric grid:

- Higher mobility of people- Electric vehicles charging infrastructure

- Renewables Energies- Booming of internet -> large data centres

Smart Infrastructures are also „lighter“ infrastructures


“power electronics based” transformer in traction application

Main concern:• Reduce volume and weight• Efficiency improvement

Traditional solution• LF transformer (16 2/3 Hz) – very bulky and heavy• Low efficiency: 90 ~ 92 %• Around 7tons


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)

“power electronics based” transformer in distribution application

The Smart Transformer



A system level optimization !

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

Project Overview


Bringing valuable functionalities to the 11kV/LV network…

• Voltage regulation

• Power flow control

• Harmonic filtering

• Reactive power injection

• LVDC supply

The LV-Engine Network Concept


SST

Substation A

11kVSubstation B

11kV

NOP

0.4kV0.4kV

P &

Q c

ontr

ol

Voltage control

SST

Substation A 11kV

Substation B 11kV

NOP-1

Substation C

11kV

NOP-2

SST

0.4kV 0.4kV

0.4kV

P &

Q c

ontr

ol

Voltage control

P &

Q c

ontr

ol

Voltage control

SST

Substation A 11kV

DC

SST

Substation A 11kV

DC0.4kV Voltage

control

SST

Substation A 11kV

Substation B 11kV

NOP-1

Substation C

11kV

NOP-2

0.4kV 0.4kV

0.4kV

P &

Q c

ontr

ol

Voltage control

Scheme 1 Scheme 2

Scheme 3 Scheme 4 Scheme 5

LV-Engine Network Trial Schems


• Releases capacity within existing LV network for connection of future LCT generationand load prior to costly reinforcement.

• Provides distribution network with increased flexibility and adaptability to cope withuncertainties in how energy will be generated and consumed.

• Significant reduction in 11kV/LV network reinforcement caused by theuptake of LCTs & electrification of heat & transport sectors.

• Lay ground works for future LVDC network reducing customer losses(avoided losses of ~£100m annually by 2040 in EV charging)

Financial Savings:

• £62m by 2030• £528m by 2050• 16% of GBs 11kV/LV GM subs by 2050

Carbon Savings:

• 523 kt.CO2 by 2030• 2,032 kt.CO2 by 2050

Projected Network and Customer benefit


Architectures Classification

1-stage 2-stage 3-stage

• Based on direct matrix converter

• High power density (No DC link capacitoes)

• Limited functionalities

• Based on matrix converter• Funcionalities are integrated in the LV

side converter

• Input and output completly decoupled• More bulky elements (capacitors and

inductors)• All required functionalities are aggregated

to this structure

Classification:

Number of power processing stages



• Based on WBG semiconductors• Concept of modules and cells are

not used.• Disadvantageous for fault tolerance

scheme implemenation• No scalability in voltage

Classification:

Modularity level



• Based on single multiwinding transformer

• Cell level modularization• Simple to implement a fault tolerance scheme

• No scalability on voltage and power

Classification:

Modularity level



• Fully modular• Scalability in voltage and

power• Simple to implement a fault tolerance scheme

• More components

Classification:

Modularity level



Architecture performance comparison

Eff x Power Isolation freq x Power

• The number of power stages are not directly related to efficiency• SiC-based converter has achieved higher efficiency with high frequency• Trasformer design is also a important issue for he ST implementation


Overview - Traction

Concept:• SR LLC dc-dc converter

Prototype:• Single-phase 1.2 MVA/ 1.8 kHz• 9 modules (8+1 redundant)

Features:• Modular• Standard 6.5 and 3.3 kV IGBT• Total of 72 semiconductors

Efficiency: 96.2%Weight: 4.5 tons

• Zhao / ABB (2011)


Overview - Distribution

Concept:• Indirect matrix converter• No capacitor on the dc link

Prototype:• Three-phase 1 MVA / 20 kHz• 13.8 kV to 415 V• 4 modules in series

Features:• Modular• SiC 10 kV Mosfets• Three power stage

• Das / GE (2009)

Theoretical Efficiency: 97%



• Huang / FREEDM (2015)

Concept:• Based on 13 kV SiC Mosfets• Classic structures

Efficiency: 93.4 %Max eff: 94.59 @40% of load• Rectifier: 99%• Dc/dc: 95.5 (max of 97.3%)• Inverter: 98.6%

Prototype:• Three-phase 10 kVA / 15 kHz• 3.6 kV to 120/240 V• dc grid: 400V

6kV

Features:• Not modular• Customized 13 kV SiC Mosfet• Total of 12 semiconductors• 3 processing stages



• ETH (2011)Concept:• 3 Port SST for to improve the power management• Distribution application: 1 MVA / 10 kV to 400V

Features:• Modular• Three power stage• Available LVDC link



• HEART (2017)Concept:

• Semi-modular• Based on asimmetrical QAB• Inter-phase arrangment of the QAB

Features:• Power delivered to dc-buses is always

balanced• Multi dc-buses easly possible• Low-voltage dc-link has no double

frequency oscillation • Easy maintenance


Challenges of the DC-DC Stage

• High voltage Isolation• High Input voltage • High output current• Galvanic Isolation in Medium/High frequency• Power flow control – dc link control• Dc breacker feature (short circuit current

proctection)

DC-DC Stage: The most challenge stage

IsolationEfficiencyCost

Deserves more attention


Implementation: DC-DC Stage

Dual-Active-Bridge (DAB) Series-Resonant Converter (SRC) Multicell converter

•Less number of HF transformer

•Operates similarly to eh DAB converter

•Easy to control (degree of freedom)•Efficiency: ~ 97%

•Open loop operation (no control / less sensors)

•Efficiency: ~ 98%

• Operate at high frequency and high power

• Most challenging converter: high voltage in the MV side and current in the LV side

.


DC-DC Stage: Implementation Concept

• Low voltage/current rating semiconductors• Scalability in voltage/power• Fault tolerance capability• Reduced dV/dt and dI/dt

• Fewer number of components• High Voltage WBG devices• Simple control/communication system

Non-Modular Vs Modular


Challenges of the DC-DC Stage

• High Voltage Isolation• Bidirectional power flow• Galvanic Isolation in Medium/High frequency• Power flow control – dc link control• Dc breacker feature (short circuit current

proctection)

DC-DC Stage: Building Block Converter

Efficiency


Review on high efficiency dc-dc converter

Relevant converters: Phase-shift Full-Bridge Series-Resonant Converter

Dual-Active-Bridge Multiple-Active-Bridge


Special Section Scope

Topics DC-connectivity in MV and MW range

Impact of asynchronous AC networks

Modular and non-modular approaches

Direct and indirect conversion

Feasibility and impact of 10 kV SiC


Special Section Program- Part 1

Short Introduction to the Smart Transformer Technology, Marco Liserre, University of Kiel, Germany

15 min 12:30-12:45

1. Medium voltage direct power conversion for medium voltage solid state transformer, Alex Huang, University of Texas at Austin, USA, 25 min 12:45-13:10

2. Intelligent Solid-State DC Substation for Flexible Electrical Grids, Rik W. De Doncker, RWTH Aachen University, Aachen, Germany, 25 min 13:10-13:35

3. Measuring Impact of WBG Semiconductors on Solid State Transformers, Deepak Divan, GeorgiaTech, USA, 25 min 13:35-14:00

Short Discussion 10 min 14:00-14:10



5. Medium-Voltage Asynchronous Microgrid Power Conditioning System Enabled by HV SiC power devices, Subhashish Bhattacharya, NC State University, USA, 25 min 14:20-14:45

6. A Bidirectional Isolated DAB DC-DC Converter Using 1.2-kV 400-A SiC-MOSFET Modules WithoutSBD, Hirofumi Akagi, Tokyo Institute of Technology, Japan, 25 min 14:45-15:10

7. Design and Experimental Analysis of a 10 kV SiC MOSFET Based 50 kHz Soft-Switching Single-Phase 3.8 kV AC / 400 V DC Solid-State Transformer, Johannes Kolar, ETH, Switzerland, 25 min 15:10-15:35

8. 10 kV SiC MOSFET based power electronics building blocks (PEBB) for modular medium-voltagegrid-tied converter, Rolando Burgos, VirginiaTech, USA, 25 min 15:35-16:00

9. A Semi-modular-based and SiC-based Smart Transformer, Marco Liserre, University of Kiel, Germany, 15 min 16:00-16:15

Short Discussion 10 min 16:15-16:25

smart transformers: which impact of the sic technology

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