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Inverters with Capacitive Output
Impedance (C-inverters)
Yu Zeng
Supervisor: Prof. Qing-Chang Zhong Department of Automatic Control and System Engineering
The University of Sheffield
UKACC PhD Presentation Showcase
Univ logo UKACC PhD Presentation Showcase Slide 2
Content
Background and Motivation
Controller Design to Achieve C-Inverters
Experimental Results
Conclusion and Future Work
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An inverter is an electrical power converter that changes a DC source
into an AC source.
UKACC PhD Presentation Showcase Slide 3
Background and Motivation
Smart grids
DGs and renewable
energy sources
Univ logo
An inverter is an electrical power converter that changes a DC source
into an AC source.
UKACC PhD Presentation Showcase Slide 4
Background and Motivation
Smart grids
DGs and renewable
energy sources
Inverters are widely
used to integrate the
distributed generations
(DGs) and renewable
energy sources into
smart grids.
Univ logo
An inverter is an electrical power converter that changes a DC source
into an AC source.
UKACC PhD Presentation Showcase Slide 5
Background and Motivation
Smart grids
DGs and renewable
energy sources
Inverters are widely
used to integrate the
distributed generations
(DGs) and renewable
energy sources into
smart grids.
How to control inverters
to achieve good power
quality is critical for
these applications. The
output impedance of the inverter plays an important role.
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The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
UKACC PhD Presentation Showcase Slide 6
Background and Motivation
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The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
UKACC PhD Presentation Showcase Slide 7
Background and Motivation
L-inverter
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The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
UKACC PhD Presentation Showcase Slide 8
Background and Motivation
It could be designed to be resistive
L-inverter
R-inverter
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The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
R-inverters achieve better
power quality than L-inverters.
UKACC PhD Presentation Showcase Slide 9
Background and Motivation
It could be designed to be resistive
L-inverter
R-inverter
Univ logo
The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
R-inverters achieve better
power quality than L-inverters.
UKACC PhD Presentation Showcase Slide 10
Background and Motivation
It could be designed to be resistive
Can the output impedance
of the inverter be designed
capacitive?
L-inverter
R-inverter
C-inverter?
Univ logo
The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
R-inverters achieve better
power quality than L-inverters.
UKACC PhD Presentation Showcase Slide 11
Background and Motivation
It could be designed to be resistive
Can the output impedance
of the inverter be designed
capacitive?
L-inverter
Yes!
R-inverter
C-inverter?
Univ logo
The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
R-inverters achieve better
power quality than L-inverters.
UKACC PhD Presentation Showcase Slide 12
Background and Motivation
It could be designed to be resistive
Can the output impedance
of the inverter be designed
capacitive?
L-inverter
Yes!
Why do we need C-inverters?
R-inverter
C-inverter?
Univ logo
The output Impedance of the inverter is the equivalent impedance looking
back into the output terminals of the inverter.
R-inverters achieve better
power quality than L-inverters.
UKACC PhD Presentation Showcase Slide 13
Background and Motivation
It could be designed to be resistive
Can the output impedance
of the inverter be designed
capacitive?
L-inverter
Yes!
Why do we need C-inverters?
They achieve better power
quality than L-inverters and
R-inverters.
R-inverter
C-inverter?
Univ logo UKACC PhD Presentation Showcase Slide 14
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
Univ logo UKACC PhD Presentation Showcase Slide 15
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
Univ logo UKACC PhD Presentation Showcase Slide 16
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
fu u
Univ logo UKACC PhD Presentation Showcase Slide 17
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
fu u
Univ logo UKACC PhD Presentation Showcase Slide 18
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
fu u small oC
Univ logo UKACC PhD Presentation Showcase Slide 19
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
fu u small oC
Univ logo UKACC PhD Presentation Showcase Slide 20
Controller Design
The output impedance of an inverter can be designed to be capacitive
via the feedback of the filter inductor current through an integrator.
fu u small oC
could be designed to optimise the voltage quality: oC
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The instantaneous Output Voltage
UKACC PhD Presentation Showcase Slide 21
Experimental Results
The Output Voltage Total Harmonic Distortion (THD)
(a) C-inverter (b) R-inverter
(a) C-inverter (b) R-inverter
Univ logo UKACC PhD Presentation Showcase Slide 22
Conclusion and Future Work
Conclusion: The output impedance of an inverter can be designed to be
capacitive.
C-inverters achieve better voltage quality than L-inverters and R-
inverters.
Univ logo UKACC PhD Presentation Showcase Slide 23
Conclusion and Future Work
Conclusion: The output impedance of an inverter can be designed to be
capacitive.
C-inverters achieve better voltage quality than L-inverters and R-
inverters.
Current Achievements: Design to optimise the voltage quality.
Parallel operation of C-inverters.
Active capacitors implemented by inverters.
oC
Univ logo UKACC PhD Presentation Showcase Slide 24
Conclusion and Future Work
Conclusion: The output impedance of an inverter can be designed to be
capacitive.
C-inverters achieve better voltage quality than L-inverters and R-
inverters.
Future Work: Parallel operation of combinations of L-inverters, R-inverters and
C-inverters.
Find out an universal droop controller for inverters with different type
of output impedance.
Current Achievements: Design to optimise the voltage quality.
Parallel operation of C-inverters.
Active capacitors implemented by inverters.
oC
Univ logo UKACC PhD Presentation Showcase Slide 25
Acknowledgement
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.
Industrial Partners:
