Journal of Scientific & Industrial Research
Vol 74, June 2015, pp. 354-357
S Karunambigai 1 *, K Geetha 2 and H A Shabeer 3
*1 Tirupur Electricity Distribution, Tirupur- 641604, Tamil Nadu, India
2 Karpagam Institute of Technology, Coimbatore-641105, Tamil Nadu, India
3 AVS Engineering College, Salem-636008, Tamil Nadu, India
Received 5 March 2014; revised 27 December 2014; accepted 6 April 2015
The need to generate pollution free energy has triggered the effect towards the usage of solar energy interconnection with the grid. Consequently, the Photovoltaic [PV] panel interfaced with the grid causes the power quality problems such as a harmonics, voltage sag etc., Active power filters are the powerful tool for mitigation of harmonics. This proposed work describes the methodology for improving power quality of the grid interfaced with renewable energy. The inverter used in this methodology can also be used as a power converter for injecting power from solar to grid along with harmonic compensation. The proposed concept is validated through dynamic simulation using MATLAB/Simulink Power system toolbox.
Keywords:
Power Quality, Active Power Filter, Fuzzy controller, harmonics compensation
Introduction
Increase in demand for power and depletion of conventional energy sources have made it necessary to move towards the renewable energy sources for power generation. Among the renewable energy sources, solar energy is available in abundance and the photovoltaic cell generates electric power directly from the solar energy. The incursion of photovoltaic cells with the distribution grid may cause thread to the power quality issues. For the improvement of power quality issues, Traditional controllers such as passive filters such as synchronous capacitors and phase advances can eliminate harmonics 1 . But they possess reasonable problems, bulkiness, electromagnetic interface and fixed compensation. Apart from traditional controller, the shunt APF are used to compensate reactive power, harmonic current 8,12,3,14 . So Efforts have been made to combine shunt active filter with the gird interfaced to renewable energy source.
Many researches have a made research on control strategies of grid interfaced renewable energy 5,7,6,11,4 .
This work proposes and validates an enhanced control Strategy of multilevel shunt active filter for solar system interfaced with the grid. In this proposed technique, the grid interfaced inverter can
__________
 Author for correspondence
E-mail:skarunambigai@yahoo.com be effectively utilized to transfer the active power from the renewable resource along with the compensation of reactive power and load current harmonics.
System Description
The proposed system consists of PV array connected to dc link of a grid interfacing inverter. The photovoltaic energy source delivers power at variable low voltage. Hence, the generated power needs power conditioning before connected to dc-link .
PV Energy Conversion
PV arrays are coupled to the DC bus and parallel to
DC-bus capacitor. The amount of power injected from
PV panels is determined by the PV output voltage.
The MPPT control circuit maximizes the PV output.
The PV output voltage and current are measured by using a sensor at the PV output terminal. Then, the
PV output power is calculated by multiplying the PV voltage and current. The MPPT controller is to set up the DC-bus voltage corresponding to the PV maximum power.
Inverter Deign
The inverter is a key element of system as it interfaces a PV panels to the grid and delivers power. The diode is used as the clamping device to clamp the dc bus voltage. For a N level diode clamped inverter, for each leg 2 (N-1) switching

∆e/e
NB
NM
NS
ZE
PS
PM
PB
KARUNAMBIGAI et al
.: POWER QUALITY IMPROVEMENT OF SOLAR SYSTEM devices, (N-1) * (N-2) clamping diodes and (N-1) dc link capacitors are required. The diodes are used to
355 inputs have seven subsets a rule base formulated for this application is given in table 2. make the connection with the point of reference
0 to obtain Midpoint voltages. Three kinds of voltage level V d/2, 0 and −V d/2 can be output corresponding to three kinds of switching states
A, 0, B, listed in table 1.
In the operation of APF, APF should correctly trace the reference so that the source current will be free from harmonic. This APF will draw small power from the source to compensate the switching loss and capacitor losses, so the DC voltage of each converter should be balanced filter 9, 10
2 . Studies have been conducted on fuzzy logic controller for shunt active
. Thus dynamic characteristics of the fuzzy controller being fast and robust over traditional controller, this work proposes Fuzzy controller for dc voltage control in APF.
Reference Current Generation
The reference current has great impact on steady state performance of the SAF. In this scheme, synchronous reference frame theory [SRFT] is used to calculate the reference current. SRFT transforms the three phase voltage and current into stationary reference frame using Park’s transformation. The d-q transformation output depends upon the load currents and the PLL circuit. The PLL provides sinθ and cosθ for synchronization. If AC source currents are I sa
, I sb
, I sc
, load currents are I
La filter compensating currents are I fa
, I
Lb
, I
, I fb
, I fc
Lc
and the
then the load currents are converted into d-q reference frame is shown in the equation (1)
I d
=√2/3 [cos θ I
La
+ cos (θ-2П/3) I
Lb
+ cos (θ+2П/3) I
Lc
]
Fuzzy Based DC Voltage Control
Variable which represents the dynamic performance of the system to be controlled is chosen as input to the controller 13 . Generally error and the change in error controller input. In this, the capacitor voltage and its derivative are considered as the input of fuzzy controller and the I max is taken as the output of the controller. The proposed controller implements mandani’s fuzzy inference method and centroid defuzzification for fuzzification and defuzzification process. The fuzzy values are presented by triangular membership function having linguistic variable of NL
(Negative Large), NM (Negative Medium), NS
(Negative Small), ZE (Zero), PS (Positive Small), PM
(Positive Medium) and (Positive Large. As both the
A
O
B
Switching
States
Table 1-Switching states of inverter
Output
Voltage
V d
/2
-V
0 d
/2
IGBT1 IGBT2 IGBT3 IGBT4
ON
OFF
OFF
ON
ON
OFF
OFF OFF
ON OFF
ON ON
I q = √2/3
[ sin θ I
La
- sin (θ- 2П/3) I
Lb
-sin (θ+2П/3) I
Lc
]
I dh
=I
L
-LPF (I d
I fa
* = √2/3 [cos θ I dh
+ sin θ I qh
]
… (1)
These currents composed of DC component and harmonic component. These d-q currents are passed through LPF which allows only the fundamental frequency component thereby eliminating harmonic component of the load current. Thus the harmonic component obtained using LPF is shown in equation (2).
) I qh
=I
L
-LPF (I q
) … (2)
The LPF is designed using second order Butterworth filter with a cut off frequency of 75 Hz. The output of the fuzzy controller is subtracted from harmonic component of direct axis in order to eliminate the steady state error. The inverse transformation from d-q to a-b-c is achieved through equation (3).
Table 2- Rule Base of Fuzzy Controller
I fb
* = √2/3 [cos (θ-2П/3) I dh
- sin (θ-2П/3) I qh
] … (3)
I fc
* = √2/3 [cos (θ+2П/3) I dh
- sin (θ-2П/3) I qh
]
NB NM NS ZE PS PM PB
NB NB NB NM NM NS ZE
NB NB NM NS
NB NM NS
NM
NM
NS
ZE
NS
NS
ZE
PS
NS
ZE
PS
NS
ZE
PS
PS
NS ZE PS
ZE PS PM
PS
PS
PS PM
PM PB
PM PB PB
PM PM PB PB PB
Thus, the AC components of d axis and q axis are used for harmonics elimination and reactive power compensation.
PWM Three-Level Inverter Control
The PWM controller calculates the difference between the injected current and the reference current.

356 J SCI IND RES VOL 74 JUNE 2015
This difference is compared with two identical carrying triangular waves shifted one from other by a half period of chopping and generate switching pulses.
Simulation Result and Analysis
The test consists of a three phase AC source of voltage 4500 v (peak) and 50 Hz frequency to a nonlinear diode rectifier load through a source and line combined reactance of 15mH/Phase. The R-L
Load on the DC side of diode rectifier is about
20 ohm and 0.1 mH. The simulation results of the proposed multilevel inverter based SAPF compensation. The Figure 1 shows the single phase voltage and current waveforms after compensation.
The three phase compensating currents of multilevel inverter based SAPF compensates the load current harmonics and thus the source current approached to sinusoidal is shown in Figure 2. The
THD in source current is reduced to 0.57% as shown in Figure 3. Thus, the multilevel inverter based SAPF successfully injects the power from solar panel into the grid along with harmonic compensation.
Fig.1-voltage and current waveforms after compensation
Fig.2-Three phase source current after compensation
Fig.3-Harmonic Spectrum of Source Current of SAF with controller

Conclusion
The proposed system couples a PV arrays with shunt active power filter (SAPF). This approach not only accomplishes the harmonic compensation, but also transfers the active power at unity power factor to the grid. It can be used to fuse real power generated from renewable energy source to the grid and function as a
SAPF. From the simulated results, it is obvious that the proposed method can be efficiently used for reactive power compensation and current harmonics reduction along with injection of active power from solar energy.
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