Universal Droop Controller for Inverters Operated in Parallel

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Universal Droop Controller for

Inverters Operated in Parallel

UKACC PhD Presentation Showcase

Yu Zeng

Supervisor: Prof. Qing-Chang Zhong

Control and Power Systems

Dept. of Automatic Control and Systems Engineering

The University of Sheffield

Control and Power Systems

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Outline

Background and motivation

The output impedance of the inverter

The universal droop controller

Simulation results

Conclusion and future work

Control and Power Systems

Univ logo UKACC PhD Presentation Showcase Slide 3/15

What is an inverter?

Inverter

DC source AC output

www.xantrex.com www.theengineeringprojects.com www.victronenergy.com

Control and Power Systems

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Micro Grids

www.diytrade.com

www.marlec.co.uk

Wind Turbine

Solar Panel

Fuel Cell

Micro

Grids

AC

DC

Inverter

AC

DC

Inverter

AC

DC

Inverter

www.engadget.com

Utility Grid

AC Load

DC

AC

converter

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Parallel operation of inverters

Micro

Grids

AC

DC

Inverter 2

AC

DC

Inverter 3

AC

DC

Inverter 1

AC Load

10 kVA

S1*=4 kVA

S2*=6 kVA

S3*=10 kVA

Univ logo Slide 5/15

Parallel operation of inverters

Micro

Grids

AC

DC

Inverter 2

AC

DC

Inverter 3

AC

DC

Inverter 1

AC Load

10 kVA

S1*=4 kVA

S2*=6 kVA

S3*=10 kVA

S1=2 kVA

S1=3 kVA

S1=5 kVA

Power sharing

Without communication

Univ logo Slide 5/15

Parallel operation of inverters

Micro

Grids

AC

DC

Inverter 2

AC

DC

Inverter 3

AC

DC

Inverter 1

AC Load

10 kVA

S1*=4 kVA

S2*=6 kVA

S3*=10 kVA

S1=2 kVA

S1=3 kVA

S1=5 kVA

Power sharing

Without communication

Droop Controller

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Control and Power Systems

Different types of output impedance

UKACC PhD Presentation Showcase Slide 6/15

Because of the filter inductor,

it is inductive

L-inverters

R-inverters C-inverters

PWM

i

L

IGBT

bridge

u C

+ - V DC

u f

AC bus

CB

vo

~ E

oZ 0oV

( rv ) ( ov )

oi

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Different droop controller forms

Inverters with inductive output impedance (L-inverters)

Inverters with capacitive output

impedance (C-inverters)

Inverters with resistive output

impedance (R-inverters)

i

Pi 0

*

Pi*

iii QnEE *

Ei

Qi 0

E*

Qi*

iii Pm *

Inductive Capacitive

Ei

Pi 0

E*

Pi*

iii PnEE *

i

Qi 0

*

Qi*

iii Qm *

Inductive Capacitive

i

Pi 0

*

Pi*

iii QnEE *

Ei

Qi 0

E*

Qi*

iii Pm *

Inductive Capacitive

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Parallel operation of L-, R-, C-inverters

Micro

Grids

AC

DC

R-Inverter

AC

DC

C-Inverter

AC

DC

L-Inverter

How to operate inverters with

different types of output

impedance in parallel?

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Parallel operation of L-, R-, C-inverters

Micro

Grids

AC

DC

R-Inverter

AC

DC

C-Inverter

AC

DC

L-Inverter

How to operate inverters with

different types of output

impedance in parallel?

Droop controller with the

same form

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Droop controller with the same form

UKACC PhD Presentation Showcase Slide 9/15

Control and Power Systems

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Droop controller with the same form

UKACC PhD Presentation Showcase Slide 9/15

Control and Power Systems

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Droop controller with the same form

UKACC PhD Presentation Showcase Slide 9/15

Control and Power Systems

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Droop controller with the same form

UKACC PhD Presentation Showcase Slide 9/15

Control and Power Systems

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Universal droop controller

UKACC PhD Presentation Showcase Slide 10/15

-

vri

s

1

*

vo

i

Ei

it+ i

Pi

Qi

ni

mi

eK -

E*

RMS

s

1

Control and Power Systems

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Simulation results (L&L, R&R)

UKACC PhD Presentation Showcase Slide 11/15

Reactive Power

Parallel operated L-inverters Parallel operated R-inverters

Active Power

Control and Power Systems

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Simulation results (C&C, L&R)

UKACC PhD Presentation Showcase Slide 12/15

Reactive Power

Parallel operated C-inverters Parallel operated L-and R-inverters

Active Power

Control and Power Systems

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Simulation results (L&C, R&C)

UKACC PhD Presentation Showcase Slide 13/15

Reactive Power

Active Power

Parallel operated L- and C-inverters Parallel operated R- and C-inverters

Control and Power Systems

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Conclusion and future work

Conclusion:

A universal droop controller that facilitates the parallel

operation of inverters with different types of output impedance

is presented.

It is with a E ∼ P and f ∼ Q droop.

Accurate load sharing can be achieved.

Future Work: Improvement on universal droop controller.

Control and Power Systems

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EPSRC Grant EP/J01558X/1 on Developing Fundamental

Theory and Enabling Technologies for Parallel Operation of

Inverters to Facilitate Large-scale Utilisation of Renewable

Energy.

EPSRC Grant EP/J001333/2 on International Collaboration

Sabbatical: To Foster Long term Collaboration with Leading

Control and Power Electronics Experts in the USA.

Industrial Advisory Board Members:

UKACC PhD Presentation Showcase Slide15/15

Acknowledgement

Control and Power Systems