Power Electronics for Distribution Grid and WBG Opportunities

Fred Wang University of Tennessee and Oak Ridge National Lab

NIST/DOE Workshop on MV WBG Power Electronics for Advanced Distribution Grids

NIST, Gaithersburg, MD April 15, 2014

Power Grid Wide Area Control of

Power Grid with High RES Penetration

Measurement &Monitoring

Communication

Actuation

Communication

FDR PMU

Storage

HVDC

Wind Farm

FACTS

Solar Farm

Responsive Load

CURENT Vision

2

Smart and Flexible Microgrid

PCC

PCC

PCC

Local protective devices

Local controllers

Microgrid central controller

System control

Normal open smart switch Normal closed smart switch

Electrical network Communication and control network

3

Reconfigurable Grid Emulator

4

Reconfigurable Grid Emulator

5

Power Electronics for Distribution Grid – Custom Power

• Power system conditioning and compensation

• Power flow control/interruption

SSTS SSCB SSFCL

• Active filters

SVC TCVR DSTATCOM DVR

Shunt AF UPQC 6

Power Electronics for Distribution Grid – Emerging Needs

• Microgrid (AC or DC)

• RES Interface

• Energy Storage/Charging

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Power Electronics for Distribution Grid – More Recent Development

Solid-state Transformer Controllable Network Transformer

Continuously Variable Series Reactor 8

HV WBG Devices in MV Applications

Applications should take advantages of • Low loss • Fast switching speed • High frequency application

Benefits of HV SiC can be realized in several ways • Direct substitution – improved efficiency and power density

• Simplified topology – further loss reduction and increased power density

• Enable new capability and functionality for system-level

• Enable new applications or replace the non-PE equipment

Wide band-gap (WBG) vs. Silicon • High breakdown electric field, high voltage rating, low conduction loss • Fast switching speed, high switching frequency • Superior thermal characteristics

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Impact of DC Breaker Speed

10

With Fast DC Breaker

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Cur

rent

(p.u

.)

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Cur

rent

(p.u

.)

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Cur

rent

(p.u

.)

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Time(s)

Cur

rent

(p.u

.)

VSC 3

AC Grid I

VSC 1

VSC 4 VSC 2

AC Grid II

Wind Farm I

Wind Farm II

DC cable 1

DC cable 2

DC

cable 4

DC

cable 3

With Slow DC Breaker VSC 1 AC Currents

VSC 2 AC Currents

VSC 3 AC Currents

VSC 4 AC Currents

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Cur

rent

(p.u

.)

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Cur

rent

(p.u

.)

0.9 1 1.1 1.2 1.3 1.4-2

0

2C

urre

nt (p

.u.)

0.9 1 1.1 1.2 1.3 1.4-2

0

2

Time(s)

Cur

rent

(p.u

.)

VSC 1 AC Currents

VSC 2 AC Currents

VSC 3 AC Currents

VSC 4 AC Currents

Impact of Switching Frequency on Stability

is

it

vt

+

−

Yoc

Zg vg

+

−

Inverter Grid

196° (unstable)

162° (stable)

Passive region

Inverter admittance Yoc (with fsw = 10 kHz)Grid admittance Yg

Inverter admittance Yoc (with fsw = 20 kHz)

Frequency [Hz]

Phas

e [D

egre

e]M

agni

tude

[dB

]

Time [s]

Grid current

Inverter current

[A]

[A]

Time [s]

Grid current

Inverter current

[A]

[ A]

fsw = 10 kHz

fsw = 20 kHz

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WBG Potential Applications in Distribution Grid

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• Improve the performance of the existing PE equipment Efficiency improvement for all; density improvement for some;

performance improvement (e.g. CB)

• Replace non-PE equipment SST

• Enhance functionality/capability Smart inverter

• Enable new applications DC grid high bandwidth conditioner direct-tied PV inverter

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Potential Research Needs • A benchmark study to understand the system benefits of HV SiC

for distribution grid applications and help to identify the potential early adopters and killer applications.

• System architecture, topology and control of the identified applications

• Identify the required performance characteristics of HV SiC and associated components and subsystems for grid applications:

Required and/or desired SiC device characteristics and performance (normal and abnormal conditions)

Control and protection

Passive components and filters (for dv/dt, di/dt, EMI etc.)

Thermal management

Standardization/building block for cost and reliability?

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Acknowledgements

This work was supported by the ERC Program of the National Science Foundation and DOE under NSF Award Number EEC-1041877 and the CURENT Industry Partnership Program. Other government and industry sponsors are also acknowledged.

Thank You!

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