Enhancement of Power Quality in Grid Connected Photovoltaic System Using Predictive Current Control Technique

International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 5 Issue: 7 549 – 553
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549
IJRITCC | July 2017, Available @ http://www.ijritcc.org
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Enhancement of Power Quality in Grid Connected Photovoltaic System Using
Predictive Current Control Technique
Neha Bhole,
SSBT‟S COET Bhambhori, Jalgaon.
North Maharashtra University
bholeneha21@gmail.com
Dr. P. J. Shah
Professor of Electrical Engineering Dept.
SSBT‟S COET Bhambhori, Jalgaon.
North Maharashtra University
pjshahj@yahoo.com
Abstract—Now- a days the increased use of power electronic devices has resulted in power quality problems such as voltage sag, swell,
harmonics and voltage flicker. Non-linear loads affect system power quality. PV systems are grid connected via an interfacing converter. Single
phase shunt active power filter (APF) can be used to develop the power quality in terms of current harmonic mitigation and reactive power
compensation. In this paper a PV interfacing inverter which acts as a shunt an APF is controlled using predictive current control (PCC)
technique for current harmonics mitigation. The MATLAB Simulink model is used to study the performance of system.
Keywords-PV system, Power quality, Shunt APF, Predictive current control (PCC), Total harmonic distortion (THD).
__________________________________________________*****_________________________________________________
1. Introduction
The power quality issues are obtained in power system
and one of them is harmonics that influence to a great extent
transformer overheating, rotary machine vibration, voltage
quality degradation, damage of electric power components,
and faulty medical facilities [1]. According to IEEE 519,
harmonic voltage distortion on power system 69 kV and
below is limited to 5.0% total harmonic distortion with each
individual harmonic limited to 3%. The current harmonic
limits vary based on the short circuit strength of the system
they are being injected into. Essentially, the more the system
is able to handle harmonic currents, the more the customer is
allowed to inject. The goal of applying the harmonic limit
specified in IEEE 519 is to prevent one customer. The
intensive use of nonlinear loads, power quality improvement
are important consideration and the limitations required by
international standards according to IEEE519-
1992[2].Those limitations were set to limit the disturbances
and escape major problems in electrical power system. Since
linear or non-linear single-phase loads are quickly
increasing, zero sequence component and current harmonics
are produced. This causes overheating of the associate
distribution transformers that may lead to a system failure,
especially in weak networks [3]-[5].
There is an increase in electric power demand in the
world. The energy obtained from conventional sources such
as coal is accompanied with environmental pollution. The
fossil fuels are non-renewable. So the entire world is
looking towards non-renewable sources of energy like solar
PV systems, wind energy, tidal energy. These sources of
energy are clean, free from environmental pollution and are
renewable. These energy sources are used with distributed
Generation (DG).There is also an increase in non-linear
loads used in industrial and domestic applications. Non-
linear loads affect system power quality such as voltage sag,
voltage swell, current harmonics, and voltage flicker.
Overheating of transformers, rotary machine vibrations,
malfunctioning of electric power equipment‟s and medical
facilities, saturations of distribution transformers are the
effects of harmonics in system. In order to avoids these
effects, the IEEE has imposed certain standards and
limitations on the maximum allowable DC currents injected
into the grid IEEE 519-1992. The harmonic current can be
blocked by using a passive or APF [6]. Passive filter are
used due to some advantages such as their simplicity, ease
of maintenance and low cost. However, it has several
drawbacks like the risk of series and parallel resonances,
system impedance dependency and aging effect of the filter
passive components. Generally, APFs sort out the classical
problems of passive filters [7]. Shunt APF can be used to
mitigate both of the line current harmonics and the neutral
current in order to improve the system power quality and
enhance the grid connection [8].The single-phase shunt APF
uses a predictive current control technique to mitigate of the
grid current harmonics as well as improve the power factor.
The suggested control strategy provides a multifunction
with a simple controller incorporating phase locked loop
independency, less sensors, ease of practical
implementation, and reduced system size and cost. This
paper discusses the predictive current control technique of
inverter current control to mitigate current harmonics and
improve power factor. The MATLAB SIMULINK modelis
used to study the performance of the system.

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2. System Descriptions
There are two configurations to connect the PV
system to the grid; two stage and single stage PV system. A
conventional two stage system has a DC-DC converter
directly coupled with PV array and grid connected inverter.
A single stage PV system consists of a DC-AC inverter
whose control is complex. In spite of having complex
control a single stage system is more efficient and cheaper
as compared to a two stage system.In this paper, a single
stage system is used. In this system, the inverter is
controlled using a predictive current control technique for
current harmonics mitigation. For connection PV system to
the grid, there are three commonly used grid interactive PV
systems; the centralized inverter system, the string inverter
system and the AC module / the Module Integrated
Converter (MIC) system. Among these, the MIC system
offers “plug and play” concept as well as significantly
optimizes the energy yield. Also the MIC idea has become
the trend for the future PV system development but
challenges remain in terms of cost, reliability and stability
for the grid connection. Usually single-phase shunt APF
usages an inverter for harmonics elimination as well as
reactivepower compensation [9]-[10].A grid connected PV
systemwith active power filtering feature has been presented
in [11]-[13].The single-phase shunt active power filter
(APF) uses a predictive control technique to mitigate of the
grid current harmonics and improve the power factor.
However, measuring the load current is mandatory. Figure 1
shows general block diagram of grid connected PV unit.
Figure 1 General block diagram of grid connected PV unit
Figure 2 shows the single phase single stage grid connected
system with control signals. It consists of PV array, inverter,
PWM, inverter control, nonlinear load and grid.
Figure 2 Overall systems modeling with control signal
3. Controller Design
The projected system shown in figure 3 consists of
PV array, DC-link capacitor, and a multifunctional inverter
connected at the point of common coupling to a single-phase
grid through the interface inductances. The compensator
reference current is calculated from the sensed grid current
drawn by nonlinear and single-phase loads connected to the
grid. The reference current is calculated by using capacitor
voltage control. The compensation objective is to
compensate for load current harmonics, reactive power
compensation and to control the DC bus during bidirectional
active power exchange between the DC side load or source
and the power system grid. The controller is used to obtain
the predicted voltage at the (𝐾 + 1)𝑡ℎ
instant. This predicted
voltage is compared with repeating sequence to generate the
gate pulses for the inverter. The proposed control system is
shown in figure 3. The multifunctional inverter is controlled
with a predictive control scheme. It needs the measurement
of the grid voltage and grid current at PCC and the inverter
DC-link voltage. The measurement of the load current and
the injected inverter current are not essential. The inverter
reference current is removed using DC-link capacitor
voltage control method.The DC-link voltage, 𝑉𝑑𝑐 are
subtracted from the reference voltage 𝑉𝑑𝑐
∗
. A PI-controller
acts on the resultant error. The DC-link voltage is
maintained constant and the power balance between the
grid, inverter, and the load is achieved as the capacitors
compensate instantaneously the difference between the grid
and the load power.

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Figure 3 Block diagram of proposed control system
The predicted controller voltage in terms of reference
current, measured grid current is given by
𝑉𝐶
∗
𝐾 + 1 = 𝐿𝑖
𝑖 𝑠 𝐾 −𝑖 𝑠
∗ 𝐾
𝑇𝑠
𝑉𝑔 𝐾 (1)
Where,𝐿𝑖 is the interfacing inductance, 𝑇𝑠is sampling time,
𝑖 𝑠
∗
𝐾 and 𝑖 𝑠 𝐾 are the sinusoidal reference and the
measured grid current at sampling instant k and 𝑉𝑔is the grid
voltage.
3.1 Input Voltage
For a single phase full bridge inverter output voltage is
given by,
𝑣𝑜 =
2 2
𝑛𝜋
𝑣 𝑑𝑐 (2)
Where, 𝑣 𝑑𝑐 is inverter input voltage, n is order of harmonics
and 𝑣𝑜 is the r.m.s output voltage of inverter
3.2 Generation of Reference Current
The output of PV array is compared with reference
of 420V. The reference signal is given to PI controller which
reduces steady state error. The output of PI controller
multiplied with sinusoidal signal gives the reference current
for the controller 𝑖 𝑟(k).The p.u sine wave is given by
V=1*sin 𝑤 ∗ 𝑡 (3)
𝑖 𝑟 𝑘 = 𝑒 ∗V (4)
Where, e is the output of PI controller.
3.3 Generation of Voltage
The reference current obtained is compared with current
measured from the grid. The signal obtained is scaled by a
factor
𝐿 𝑖
𝑇𝑠
and added to the measured grid voltage 𝑣𝑔 𝑘 .The
resulting signal is the predicted voltage which is compared
with repeating sequence to obtain pulses for the gate circuit
of inverter.
4. Performance Analysis of the Proposed System
The analysis of the proposed system shown in
figure 2 is simulated using a MATLAB Simulink model.
The system factors are listed in table 1.
Table1: The System Factors
Symbol Quantity Values
F Line frequency 50Hz
𝑉𝑑𝑐
∗
DC reference voltage 420V
𝑉𝑠 Grid voltage in RMS 220V
C PV module capacitor 4700µF
𝑇𝑐 Atmospheric Temperature 25ºC
𝐿 𝑠 Grid tied inductor 3.2mH
𝐶𝑑𝑐 DC bus Capacitor 5 µF
𝑅𝑖 Resistance of inverter 0.05 Ω
𝐿𝑖 Inductance of inverter 3.2mH
The controller is modeled using MATLAB Simulink for
inverter which is connected to grid and nonlinear loads.In
this paper a single phase 50 Hz full bridge inverter is
connected to grid and to nonlinear loads .For different
nonlinear loads, the currents injected into the grid have THD
less than 5% which is according to IEEE standards. The grid
current THD is compared before and after compensation.
The APF increases the THD from 3.1% to 3.2% which obey
with the IEEE Std. 519-1992.The grid current THD is
measured for different nonlinear loads. Table 2 shows grid
current THD for different nonlinear loads.
Figure 5 Simulation results: (a) Voltage drop across load,
(b) Grid current, (c) Grid voltage, (d) Predicted voltage.

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Fast Fourier Transform (FFT) Analysis:
The FFT analysis of grid current waveform for load of
impedance is 5+j 3.14 Ω and having 0.45% THD. Figure 6
shows the FFT analysis of grid Current waveform.
Figure 6 FFT analysis
Table 2: Grid current THD for different nonlinear load
Sr. No. R(Ω) L( mH) THD (%)
1 90 50 4.451
2 80 60 4.262
3 70 40 4.033
4 25 30 3.877
5 50 30 3.918
6 30 13 3.731
7 20 5 3.742
8 10 10 3.768
5. Conclusion
In this paper, a PV system is interfaced to the grid via a
multifunctional interfacing inverter. A simple Predictive
current control method is used. Predictive controller gives
better performance while the mathematical model is
accurate, linear and time invariant. The system performance
is investigated using MATLAB /Simulink model at different
case of load variation. The inverter achieves function of
supplying the available power from the PV unit into the
loads in addition to improving the power quality in terms of
grid current THD and power factor. Hence enhance power
quality in grid connected PV system with current harmonic
mitigation and reactive power compensation.
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Enhancement of Power Quality in Grid Connected Photovoltaic System Using Predictive Current Control Technique

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