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LeMenizInfotech
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The Master of IEEE Projects
Delay-Dependent Stability of Single-Loop
Controlled Grid-Connected Inverters with
LCL Filters
Introduction:
Grid-connected inverters form an important interface between
distributed power generation systems and the power grid. LCL filters
have been commonly adopted to mitigate switching harmonics
generated by the inverters. Compared with L filters, LCL filters have
better attenuating ability and allow the use of low inductance
inductors, resulting in a cost-effective solution. However, the inherent
resonance of LCL filters has the tendency to destabilize the inverter
systems. Different passive and active damping methods have been
proposed to improve system stability. The passive damping strategy
increases the power loss. The active damping methods, multiloop or
filter-based, are complex in the realization and design of the controller
Existing system:
The stability is closely related to the ratio of sampling frequency
to the LCL resonance frequency, but the nature of this relationship is
not known. The damping characteristic of the time delay in the GCF
loop, and the GCF loop can be stable if the resonance frequency is
smaller than 1 / 6 of the sampling frequency. However, only the GCF
with a delay of 1.5Ts (Ts is the sampling period) is studied. The GCF
loop is stable when the time delay is between 0.53Ts and 1.33Ts, but
this range is only valid for the controller parameters used by the
authors. A method to obtain the stable ranges of time delay for ICF
Copyright © 2016LeMenizInfotech. All rights reserved
LeMenizInfotech
36, 100 Feet Road, Natesan Nagar, Near Indira Gandhi Statue,
Pondicherry-605 005.
Call: 0413-4205444, +91 9566355386, 99625 88976.
Web :www.lemenizinfotech.com/ www.ieeemaster.com
Mail : [email protected]
The Master of IEEE Projects
and GCF loops. However, the method is not based on precise
derivation, and the deduced stable ranges, which are different to the
result, are only for specified LCL and controller parameters.
Disadvantages:
 Passive damping strategy increases the power loss
 Active damping methods are complex in the realization
Proposed system:
A Thorough theoretical study is carried out on the relationship
between the time delay and stability of single loop controlled gridconnected inverters with LCL filters. It is found that the time delay is
a key factor that affects the system stability. The main contributions
of this paper are summarized below. First, the stable ranges of the
time delay (the ranges of the time delay within which the system can
be made stable) are deduced in the continuous s-domain as well as the
discrete z domain, applicable for any LCL parameters. The present
study explains why different conclusions on the stability of the single
loop control systems are drawn in previous papers, i.e., the time delay
in these cases falls into different ranges. Furthermore, it can be
deduced that the stable ranges of time delay for the loop with
capacitor current feedback are same as those of the ICF loop.
Therefore, the study can also facilitate the analysis of the active
damping methods which employ an inner ICF or capacitor current
feedback loop. Second, to improve the stability of the single-loop
control systems, time delay compensation methods are proposed.
Copyright © 2016LeMenizInfotech. All rights reserved
LeMenizInfotech
36, 100 Feet Road, Natesan Nagar, Near Indira Gandhi Statue,
Pondicherry-605 005.
Call: 0413-4205444, +91 9566355386, 99625 88976.
Web :www.lemenizinfotech.com/ www.ieeemaster.com
The Master of IEEE Projects
Mail : [email protected]
Advantages:
 Improved stability
 High performance of the system
Applications:
 High voltage and high power transmission applications
Copyright © 2016LeMenizInfotech. All rights reserved
LeMenizInfotech
36, 100 Feet Road, Natesan Nagar, Near Indira Gandhi Statue,
Pondicherry-605 005.
Call: 0413-4205444, +91 9566355386, 99625 88976.
Web :www.lemenizinfotech.com/ www.ieeemaster.com
Mail : [email protected]
The Master of IEEE Projects
Block diagram:
Unbalanced
Load
AC
LCL filter
Input DC
supply
Three phase
inverter
Gate driver circuit
12 V
DC
Buffer circuit
5V
DC
Micro-controller
circuit
Supply
Copyright © 2016LeMenizInfotech. All rights reserved