The 6th Inteational Power Electronics Drive Systems and Technologies Conference (PEDSTC2015)
3-4 February 2015, Shahid Beheshti University, Tehran, Iran
A Modified Model Predictive Control Method for
Voltage Control of an Inverter in Islanded Microgrids
Nima Naeiji, Mohsen Hamzeh, Ashkan Rahimi Kian
School of Electrical and computer engineering, College of engineering, University of Tehran, Tehran, Iran
Department of Electrical and computer engineering, Shahid Beheshti University, Tehran, Iran
n.naeiji@ut.ac.ir, mo hamzeh@sbu.ac.ir, arkian@ut.ac.ir
Abstract-In this paper, a modified model predictive control
method has been proposed for voltage control of an inverter in
an islanded microgrid. The main objective of this method is to
reduce voltage THD and the reference tracking error. In the
proposed scheme, some vectors are added to existing vectors,
available in FCS-MPC method to reduce the error between the
reference voltage and the output voltage. In this control scheme,
the model of the system is used to predict the behavior of the
output voltage. Then based on a quadratic cost function, the
predictions are evaluated to select the optimized control signal
which should be applied to the system in the next sampling
interval. The performance of the proposed control scheme is
evaluated using MATLAB/Simulink environment.
Keywords-model predictive control; islanded microgrid; cost
function; three phase inveer
I. INTRODUCTION
In recent years, renewable energy sources such as wind and
solar energies have been increasingly employed to reduce the
consumption of fossil el and problems such as environmental
pollution. Renewable energies are usually used in disibuted
generation (DG). Interconnection between DG units and the
local loads form the microgrid systems. The microgrid can
operate in grid-connected mode or autonomous islanding mode
and benefits both the utility and customers [1]. In the grid-
connected mode, the voltage and equency are determined by
the main grid, but in islanded mode, if control methods are the
same as the grid-connected mode, the voltage and equency
will deviate om their nominal values, which might make the
microgrid unstable.
Various control techniques have been proposed to control
the ouut voltage of the inverter in islanded microgrids. In
[2],[3], an adaptive proportional resonant (PR) conoller is
used to regulate the load voltage in an islanded microgrid. In
[4], the conol sategy consists of a multi-proportional
resonant conoller whose parameters are assigned with PSO
optimization algorithm. In [5], a robust conol technique,
including H � and robust state predictor is proposed to conol
the ouut voltage of the inverter for UPS application. In [6], a
robust conoller is used to regulate the ouut voltage of the
inverter in islanded microgrid. In [7], [8], deadbeat conol is
used for the ouut voltage control of single-phase and three-
978-1-4799-7653-9115/$31.00 ©2015 IEEE 555
phase inverter. A disturbance observer for deadbeat conoller
is suggested in [9] in order to estimate the load cuent and
other sources of error. Another technique to conol the
islanded inverter is sliding mode conol [10], [11], which has
problems such as chattering in ouut control signal and
computational complexity. An adaptive control method is
proposed in [12] to control the inverter for UPS application. In
[13], a neural controller with online optimization is proposed
for UPS inverters.
Another technique to conol power converters, including
inverter is model predictive control (MPC). MPC uses a model
of the system to predict the ture ouut om cuent
measurements and control signals. Then a cost nction is used
to select the optimized control signal which has been applied to
the system in the next sampling interval. One type of MPC that
can be used in power eleconic converters, called finite conol
set MPC (FCS-MPC) and takes advantage of the inherent
discrete nature of power converters. Since the power converter
has a [mite number of switching states, the MPC optimization
problem can be simplified and reduced to the prediction of the
system behavior only for those possible switching states. Then
each prediction is used to evaluate a cost nction, and the state
with minimum cost is selected and generated [14]. In [15], a
MPC conoller is employed to regulate the ouut voltage of
four-leg inverter used in the UPS system.
In this paper, a modified FCS-MPC method is proposed for
a three-phase inverter in islanded microgrids. In the proposed
method which is called inter vector model predictive control,
some vectors are added to existing vectors, available in FCS-
MPC method, to reduce the error between the reference voltage
and the ouut voltage.
The rest of the paper is organized as follows: Section II
describes the FCS-MPC technique for ouut voltage conol of
the inverter. In section III, the proposed conol method has
been presented. Results are discussed in Section IV and
followed by conclusions in section V.
II. FCS-MPC CONTROL OF INVERTER IN ISLANDED MICROGRID
The sucture of the system is shown in Fig. 1. In this
structure, the system has one DG unit. The dynamical