A Three-Phase Inverter for a Standalone Distributed Generation System: Adaptive Voltage Control Design and Stability Analysis

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46 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 29, NO. 1, MARCH 2014
A Three-Phase Inverter for a Standalone Distributed
Generation System: Adaptive Voltage Control
Design and Stability Analysis
Jin-Woo Jung, Member, IEEE, Nga Thi-Thuy Vu, Dong Quang Dang, Ton Duc Do, Student Member, IEEE,
Young-Sik Choi, and Han Ho Choi, Member, IEEE
Abstract—This paper proposes a robust adaptive voltage control
of three-phase voltage source inverter for a distributed generation
system in a standalone operation. First, the state-space model of
the load-side inverter, which considers the uncertainties of system
parameters, is established. The proposed adaptive voltage control
technique combines an adaption control term and a state feedback
control term. The former compensates for system uncertainties,
while the latter forces the error dynamics to converge to zero. In
addition, the proposed algorithm is easy to implement, but it is
very robust to system uncertainties and sudden load disturbances.
In this paper, a stability analysis is also carried out to show the
robustness of the closed-loop control system. The proposed control
strategy guarantees excellent voltage regulation performance (i.e.,
fast transient response, zero steady-state error, and low THD) un-
der various types of loads such as balanced load, unbalanced load,
and nonlinear load. The simulation and experimental results are
presented under the parameter uncertainties and are compared to
the performances of the corresponding nonadaptive voltage con-
troller to validate the effectiveness of the proposed control scheme.
Index Terms—Adaptive voltage control, distributed generation
system (DGS), robust control, stability analysis, standalone opera-
tion, uncertainties, voltage source inverter.
NOMENCLATURE
Vi Inverter output line to line voltage vector (Vi = [ViAB
ViB C ViC A ]T
).
Ii Inverter phase current vector (Ii = [IiA IiB IiC ]T
).
VL Load line to neutral voltage vector (VL = [VLAn VLB n
VLC n ]T
).
IL Load phase current vector (IL = [ILA ILB ILC ]T
).
Vidq d–q frame voltage vector (Vidq = [Vid Viq ]T
) of Vi.
Iidq d–q frame current vector (Iidq = [Iid Iiq ]T
) of Ii.
Iidqr Reference current vector (Iidqr = [Iidr Iiqr ]T
) of Iidq .
VLdq d–q frame voltage vector (VLdq = [VLd VLq ]T
) of VL .
VLdqr Reference voltage vector (VLdqr = [VLdr VLqr ]T
) of
VLdq .
Manuscript received November 13, 2012; revised March 6, 2013, July 14,
2013, and October 16, 2013; accepted October 17, 2013. Date of publication
November 20, 2013; date of current version February 14, 2014. This work was
supported by the National Research Foundation of Korea (NRF) under Grant
2012R1A2A2A01045312 funded by the Korea government (MSIP). Paper no.
TEC-00593-2012.
The authors are with the Division of Electronics and Electrical Engineering,
Dongguk University, Seoul 100–715, Korea (e-mail: tonducdo@dongguk.edu).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TEC.2013.2288774
ILdq d–q frame current vector (ILdq = [ILd ILq ]T
) of IL .
ω Angular frequency (ω = 2π·60 rad/s) of VL .
Vdc DC-link voltage.
Lf Filter inductance.
Cf Filter capacitance.
I. INTRODUCTION
IN recent years, eco-friendly distributed generation systems
(DGS) such as wind turbines, solar cells, and fuel cells are
dramatically growing because they can fulfill the increasing
demand of electric power due to the rapid growth of the econ-
omy and strict environmental regulations regarding greenhouse
gas emissions [1]–[8]. Generally, the DGSs are interconnected
in parallel with the electric utility grid and provide maximum
electric power to the grid. However, there are some areas (e.g.,
remote islands or villages) where the connection to the grid
is expensive or impractical and then small scaled standalone
DGSs are the only efficient and economical options. In such
DGSs, depending on consumers’ power demand, there are sit-
uations where some DGSs operate in parallel [9]–[11] or inde-
pendently [12]–[14]. In either case, a stable operation of each
DGS unit is as important as the stability of the parallel operating
DGSs in which the proper load sharing of each unit is one of
main research issues since the voltage controller is commonly
used in a single DGS unit or multiple DGS units. For this rea-
son, the voltage controller design for a single DGS unit, which
can guarantee a good voltage regulation under unbalanced and
nonlinear loads, is an interesting topic in the field of the DGSs
control.
For the purpose of improving the quality of inverter output
voltage, many researchers are working on designing the con-
trollers for dc–ac power converters. In [15], a control scheme
based on the transfer function of the nominal plant is proposed
for an electronically coupled DG unit in an islanded mode. This
control method is suitable for a prespecified and balanced load
condition, but cannot cover the large load variations. In [16], a
robust controller is developed for balanced and unbalanced sys-
tems, which considers the uncertainties of the load parameters.
However, nonlinear load is not fully addressed. In [17], a repet-
itive control is used to regulate the UPS inverters. However, the
slow response and lack of the systematic method to stabilize the
error dynamics with the repetitive control are being the main
problems. In [18], an alternative control strategy with a feed-
forward compensation component can significantly mitigate the
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