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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

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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

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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

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