Efficiency Enhancement of PV based Dynamic

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 18 (2015) pp 38724-38728 © Research India Publications. http://www.ripublication.com

Efficiency Enhancement of PV based Dynamic Voltage Restorer using Zeta converter P.Rajakumar* Research scholar SELECT,VIT University, Vellore, & Assistant Professor / EEE, Sri Sairam Engineering College, Chennai. [email protected] Dr.R.Saravanakumar, Professor SELECT, VIT University, Vellore [email protected] R.Thirumalaivasan Associate Professor SELECT,VIT University, Vellore [email protected]

Abstract This exertion explains the method to improve the efficiency of photovoltaic based dynamic voltage restorer (DVR) used for reduction of voltage sink and other transients in Power distribution. Local grid Model with DVR powered from Photo Voltaic (PV) system and Zeta Inverter is developed. The Zeta inverter with reduced number of switches enhances the efficiency of DVR by effectively removing the harmonic distortion in the distribution voltage profile. In order to enhance the effectiveness of the PV system, perturb and observe (P&O) algorithm based Maximum Power Point Tracker (MPPT) is connected. This Proposed system is modeled and simulated by MATALB Simulink. The replacement of conventional Voltage Source Converter or multilevel inverter by Zeta inverter in DVR improves the system performance and yields a cost effective solution for power quality enhancement.

discontinuous control laws to drive the system state trajectory onto a specified surface in the state space, the so called sliding or switching surface, and to keep the system state on this assorted for all the subsequent times. Photo Voltaic systems can generate direct current electricity without environmental impact and contamination when exposed to solar radiation. Recently many new methods are proposed for modelling and simulation of photovoltaic arrays (PVA) having higher accuracy and lower assumptions [6]-[7]. Being a semiconductor device, the PV system is static, quiet, free of moving parts, and has little operation and maintenance costs. But due to relatively high initial cost and low efficiency, maximum power point tracking (MPPT) is essential. Accordingly many literatures have dealt on MPPT [8]. For the effective incorporation of the solar power into the power system, competent controlling method should be incorporated using power electronics devices. In this work PV power generation as input for DVR, when disturbance occurs in the system it will supply power to dump loads. It happens through different converter topologies. The zeta converter interfaced to advanced power is to use a series of power semiconductor switches with several lesser number of voltage dc sources, which is most suitable for the proposed system collecting power from PV. In section-II proposed power system model is presented and discussed. The simulation results are discussed for different conditions in section-III. Conclusion and future scope of work is given in section-IV.

Keywords-component: Dynamic Voltage Restorer, Maximum Power Point Tracker, Zeta inverter, Perturb and observe

I. INTRODUCTION The major snag in power system is voltage droop and swell, voltage flicker, transient [1]. DVR is one among the devices that have an analogous structure of sequence form of FACTS contrivance. The connotation of this contrivance is to safeguard a perceptive load from voltage droop or voltage engorges and deviations in the distribution side. This is done by the technique of quick string voltage booster. When there is a distortion in the source voltage, the proposed series device may also have to inject a distorted voltage to counteract the harmonic voltage [2]-[4].Existing methods of DVR model with the help of conventional VSC or Cascaded multilevel inverter needs multifarious intend in the control perspective point of view. The proposed system has reduced number of switches for the implementation of DVR to enhance the quality of power in the distribution side. Among the existing methods of DVR, the SMC technique has its high simplicity and robustness. A sliding-mode input–output linearization controller for the zero-voltage switching (ZVS) is presented [5]. The proposed controller extensively improves the ephemeral response and disturbance, rejection of the converter while preserving the closed-loop stability and SMC utilizes

II. PROPOSED SYSTEM MODELING The proposed power system model comprises PV system, DVR, SMC, energy storage devices and Zeta converter as shown in Fig.1. The integrated model of PV system with DVR as shown in Fig 2.

0


Fig 1 Proposed block diagram of PV based DVR for voltage alleviation.

Fig 4 Equivalent circuit of Zeta converter

Where

Tr

is the cell reference temperature, Irr is the reverse

saturation current at Trr , and

EG is the band-gap energy of a

cell. The PV current, I ph depends on irradiation level and the cell temperature as: I ph  0 . 01 I scr  K v T  T r S

(3)

Where I scr , is the cell short-circuit current at the reference temperature and radiation, Fig 2 Built-in PV based DVR.

2

A. Solar Cell Model A general dynamical analysis of I-V output characteristics of Photo voltaic cell was discussed in [6]-[8]. This equivalent circuit-based model is mainly used for the MPPT technologies. The voltage-current characteristic equation of a solar cell is given as equation (1). Equivalent circuit of generalized model of PV cell is shown in Fig 3. The ideal PV cell, the PV array can be described by the following equation [1][2] I pv  n p I

ph

  q v dc  n p I rs  exp   kTA n s 

    1   

K v is a temperature coefficient,

and S is the irradiation level in kW / m . Multiplying both sides of equation (1) by Vdc , the power delivered by the PV array is expressed as:  Ppv  n p I ph v dc  n p I rs v dc  exp 

    1  

(4)

Dynamics of the DC-link voltage are described based on the principle of power balance, as: 2 C dv dc  P pv  Pdc 2 dt

(1 )

Reverse saturation current (Irs) which varies with temperature according to the following equation: 3  qE G  1 T  1  (2) I rs  I rr   exp      Tr   kA  T r T  

 q v dc   kTA n s

(5)

B. Energy Storage Devices Energy storage unit is dependable for energy storage in DC form, Super-Capacitors, Superconducting Magnetic Energy Storage (SMES), lead acid batteries and Flywheels are generally used as energy storage devices. In proposed model energy generated from PV is stored in battery and supply to DVR at the time of unavailability of solar irradiation. C. Dynamic Voltage Restorer (DVR) DVR is the most competent and successful modern custom power device used in power distribution networks. Usually it is installed in a distribution system between the supply and the load feeder at the point of common coupling (PCC). In addition to reducing voltage dip and engorge, DVR can also ensure of ephemeral in voltage, line voltage harmonics mitigation and fault current margins. Fig.2 shows integrated PV based DVR.

Fig 3 Generalized PV circuit.

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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 18 (2015) pp 38724-38728 © Research India Publications. http://www.ripublication.com D. Zeta Converter A zeta converter is a higher order non linear system with reference to energy excitation, and it is analogous to buckboost converter and relating to the response. The ideal switch based perception of zeta converter is depicted. A nondetached zeta converter circuit is revealed. Numerous working modes are feasible for this converter depending on inductance value, load resistance and working frequency. Zeta converter is used along with VSI in this system. E. Sliding Mode Controller Sliding mode control design requires merely the collection of parameter τ. Selection, should be made with the purpose of guarantee the following three constraints (i) the hitting condition, which requires that the system trajectories cross the sliding line irrespective of their starting point in the phase plane; (ii) the existence condition. (iii) the stability condition of the system motion on the sliding line (i.e. the motion must be toward the equilibrium point). Another important consideration concerning physical systems is that not all points in the phase plane are reachable. In the previous example, since inductor Current and output voltage is always non negative, the regions under the line left of line = − ∗ are left out.

=

From equation (6) that the position error x1(t) will congregate to zero exponentially if the pole of the system is intentionally located on the left hand plane. The principle of SMC is shown in fig 5. Thus the occurrence of overshoot will not occur, and the system dynamic will behave as a state feedback control system [9]. F.MPPT Controller To achieve maximum power point tracking with the help of perturb and observe algorithm to take a sample data (k), and take previous data (k-1) and comparing these two and maintain the maximum power point track controller algorithm as shown in fig 7.

∗

and to the

Fig 7 Perturb and Observe algorithm

G.DC-DC Converter Proposed system has buck converter and it is interfaced with zeta converter PV system for maintaining the desired stiff output voltage.

Fig 5 Sliding mode for the buck converter

Fig 6 Buck converter.

If the state trajectory of system is trapped on the switching surface, namely S(t) = 0, then the equivalent dynamics of system is governed by the following equation x t

  A

 BK

X t 

III SIMULATION RESULTS AND DISCUSSIONS Simulation results are given from fig.8 to fig.11. Now, the disturbances in voltage are compared with the desired voltage. Based on this comparison, a sag and swell detector provides an error signal to the SMC. This in turn reduces the error signal to as small as a value possible. Depending upon this error signal, the modulating signal is varied which in turn changes the PWM signals obtained. Accordingly, the desired MOSFETS are gated and the necessary voltage is obtained at the inverter output. Fig 11 shows that load voltage before interfaced with DVR. Fig 12 shows that load voltage after interfaced with DVR. Fig 13 & 14 shows that THD of the proposed system without and with DVR. The inverter output is injected into the distribution lines to compensate for the sag or swell in voltage created. Voltage disturbances are sensed by the DVR and depending upon the requirement, the required switches in the inverter are triggered. This in turn makes sure that the inverter provides the necessary voltage which is injected into the distribution lines by means of a coupling transformer.

(6)

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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 18 (2015) pp 38724-38728 © Research India Publications. http://www.ripublication.com The voltage waveform after compensation by means of a DVR is shown in fig 12. It can be seen that the terms guiding power quality namely voltage and frequency are well within the limits required. In this way, the power supplied to the sensitive load is well within the limits thereby ensuring efficient operation and long life of equipments.

0.035

0. 03

0.025

TH D

0. 02

0.015

0. 01

0.005

0

-0.005

0

0.1

0. 2

0.3

0. 4

0.5 Ti me in Sec onds

0.6

0. 7

0.8

0. 9

1

Fig 14 THD of the proposed system with DVR

IV.CONCLUSION In this work, the prominence of the power in the distribution side was superior with the help of DVR, when the interlude occurs in the sensitive load feeder. Scrutiny was carried out to different custom power devices, DVR has admirable reparation for voltage disagreement. Simulation was carried out for PV interfaced with Zeta converter based DVR employing SPWM technique with MATLAB/SIMULINK. Limitless paper was worked on voltage mitigation for sag or swell, but in the probable model both are mitigated whichever is mandatory. Although it is a PV with MPPT algorithm incorporating this techniques into a DVR can significantly recuperate its recital and make sure consistent operation of the sensitive loads.

Fig 9 Simulation diagram of Zeta converter

References [1] Fig 10 Proposed simulation diagram [2] 600 Load Voltage before c om pens ation 400

V ol tage in Vol ts

200

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-400

-600

0

0.1

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0. 4


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[3]

Fig 11 Load Voltage without DVR Load Voltage Aft er C ompens at ion

500

[4]

400 300

V ol tage in Vol ts

200 100 0 -100 -200 -300 -400 -500

0

0.1

0. 2

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[5]

Fig 12 Load Voltage with DVR 0. 14 0. 12

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THD

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[6]

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Fig 13 THD of the proposed system without DVR

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