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1.0 INTRODUCTION

Presently more renewable energy systems have been implemented in power generation sector due to the environmental protectionregulations and the shortage of conventional energy sources.PV generation is the technique which usesphotovoltaic cell to convert solar energy to electric energy.Photovoltaic energy is important as arenewable energy source because of its distinctive advantages,such as simple configuration, no fuel cost,and low maintenance cost, etc. However, the disadvantage is thatphotovoltaic generationinherently depends uponweather conditions. Thus, energy storage element is necessaryto help get stable and reliable power from PV system to meet regularloads. To improve both steady anddynamic behaviors of the whole generation system, the concept of grid connected HES comes into picture.

HES are inter-connected renewable and non renewable energy sources like wind, photovoltaic,fuel cell and diesel generators to feed power to local load and connecting to grid/micro grids. Because of the inherent nature of the solar energy and the wind energy, the electric power generations of the PV array and the wind turbine are complementary. The hybrid PV & wind power system has higher reliability to deliver continuous power than individual source. HES are necessary in order to draw maximum power from PV arrays or wind turbines and to deliver stable power to the load. The PV with fuel cell generation system is another preferable option in hybrid energy generation.

To avoid battery requirement to store energy in renewable energy generation system, grid connected system is the best possible solution.

Performance study of grid-connected wind and photovoltaic hybrid energy system under variation of generation

Nagendra K*, Vinatha U**, Krishnamurthy N*** and Raghu N****

The aim of this work is to analyze typical configuration of grid connected wind and photovoltaic hybrid energy system. Nowadays hybrid energy systems (HES) are widely used because of inherent problems with solar energy. HES includes several (two or more) energy sources with appropriate energy conversion technologies connected together to feed power to local load/grid. These allowa wide variety of primary energy sources, frequently generated from renewable sources as the stand alone system for rural electrification and also for grid extension. Mainly the work presents the system response under generation variation of HES with grid interface. Application represents a useful tool in research activityand also in teaching.

Keywords: Renewable energy systems,Photovoltaic(PV) systems, Wind energy system and grid connected energy system.

* & **** Research Scholars, EEE Department, SET, Jain University, Kanakapura, Bengaluru-562112. E-mail: kbnagendra@gmail.com & raghu1987n@gmail.com**Associate Professor, EEE Department, National Institute of Technology Surathkal, Karnataka-575025. E-mail: u_vinatha@yahoo.co.in***Professor, EEE Department, SET, Jain University, Kanakapura, Bengaluru -562112. E-mail: Krishnamurthy.access@gmail.com

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The advantages of grid connected systems are it is environmental friendly due to absence of battery bank and uninterrupted supply can be given from the grid even in the absence of renewable energy generation.

The objective of this paper is to discuss about grid-connected wind and photovoltaic HES and to present performance of the modeled system under variation of generation condition.

2.0 LITERATURE REVIEW

Design and simulation of DC/DC boost converter has implemented for photovoltaic energy system connected to the isolated load by (B. M Hasaneen et al. 2008). The input of DC/DC boost converter is an unregulated DC voltage, which is obtained by distributed energy resources (DER) and it will be fluctuating due to changes in inputs of DER. The DC/DC boost converter will give regulated DC voltage.

Survey of hybrid energy systems with wind energy system has carried out by (Chen Wang et al. 2007). Majorly there are two applications of wind hybrid energy system, one is wind and photovoltaic hybrid energy system another one is wind and fuel cell hybrid energy system.

Modeling and simulation of grid-connected hybrid photovoltaic/battery distributed generation system has implemented by (Fei Ding et al. 2010). This paper gives the basics of photovoltaic system, the effect of irradiance on the I-V characteristic at constant cell temperature and the effect of temperature on the I-V characteristic at constant irradiance is discussed.

The IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems has been discussed by Standards Coordinating Committee 21 on Fuel Cells, Photovoltaics, Dispersed Generation, and Energy Storage (IEEE 1547-2003). Mainly the required parameters are discussed for grid interactive renewable energy sources implementation.

The PID Control System Analysis is carried out for closed loop control system by (KiamHeongAng et al. 2005). The objectives of PID controller are to achieve short transient and high stability. The short transient and high stability are achieved by proper tuning of Kp, Ki and Kdvalues in PID controller. In this paper the table of effects of P, I and D tuning values on rise time, overshoot, settling time, and steady state error of closed loop system response has given.

Modeling of photovoltaic arrays has been implemented by (M. G. Villalva et al. 2009). The method is used to obtain the parameters of the array model using information from the datasheet. The photovoltaic array model can be simulated with any circuit simulator. The equations of the model are presented in details and the model is validated with experimental data and simulation examples are presented.

Modeling and simulation of fuel cell based distributed generation system was implemented in (Santhoshakumar A 2010). The modeling of Proton exchange membrane fuel cell, DC/DC boost converter control and design, control of VSI from PQ control scheme for grid connection of modelled fuel cell system is discussed.

The control strategy of power converters for microgrids (MG) was implemented by (Vechiu et al. 2009). The renewable sources and the storage system are connected on DC-bus which is interconnected with a main grid trough VSI. The attention focuses on the control technique of the VSI during grid connection. Renewable energy sources with MG have been investigated on simulation using a MATLAB/Simulink model.

Different circuit topologies for grid-connected hybrid photovoltaic and Wind power systems like, The ac-shunted grid-connected hybrid PV/Wind power system, the dc-shunted grid-connected hybrid PV/Wind power system and the multi-input grid-connected hybrid PV/Wind power system are discussed by (Yaow-Ming Chen et al. 2006).

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The simulation and performance study of grid-connected wind and photovoltaic hybrid energy system has been discussed and the results are presented by (Nagendra K et al. 2014).

3.0 INTEGRATION OF PV & WIND HES TO GRID

FIG. 1 CoNFIGURATIoN oF HES [10]

The configuration of hybrid energy system is shown in Figure 1, it contains wind, photovoltaic and fuel cell power system connected to the grid. But in general case hybrid energy system can be a combination of different renewable/non renewable energy systems.

FIG. 2 BLoCK DIAGRAM oF MoDELED GRID CoNNECTED PV & WIND HES [10]

The Block diagram of modeled grid connected PV & wind HES consists of PV model with boost converter, wind model with boost converter

connected to the grid with power electronic interface. Power electronic interface consists of DC link connected to voltage source inverter (VSI), VSI output is connected through LC filter. The inverter is controlled by PQ control [10].

FIG. 3 PoWER FLoW BETWEEN A VSI AND GRID [7]

Where,

Vinv = Inverter voltage.

Vgrid = Grid voltage.

R = Resistance of filter, transformers and transmission line.

L = Inductance of filter, transformers and transmission line.

The Figure 3 shows power flow between a VSI and grid, where the impedance represents the combined filter, transformer and transmission line inductance. The active and reactive power flows from the converter are controlled by magnitude and phase of the converter output voltages relative with grid parameters. The active power flow is controlled by varying the phase difference and reactive power flow is by varying the magnitude of inverter output. The phase difference and amplitude are varied with reference of constant grid voltage. The control of modulation index controls amplitude, and synchronization and phase angle control of modulating sine wave controls the phase variation. The real and reactive power delivered to the utility is given by following relations,

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....(1)

....(2)

Where,

Inverter can be controlled typically by two ways. The active and reactive power control scheme (PQ control), when the inverter is operated to meet grid connected operation and active power and voltage scheme (PV control), when the inverter is operated to meet isolated operation. In this work the PQ control method is used to control the inverter.

4.0 SIMULATION STUDY

HES are implemented using MATLAB/Simulink and performance study has been presented under variation of HES generation with change of solar irradiation, temperature and wind speed. The load value is kept constant. The wind speed is changed from 12 m/s to 14 m/s at 0.7s, temperature is changed from 250C to 300C at 0.9s, solar irradiation is changed from 1000 W/m2 to 1800 W/m2 at 1.25s, and load parameters 100 kW active power, 60 kVAR reactive power are given as inputs to the simulated model and 415 Vr.m.s, 50 Hz is taken for grid parameter. The results are as follows:

FIG. 4 (A) DC LINK VoLTAGE

FIG. 4 (B) VoLTAGE & CURRENTS AT AC BUS

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FIG. 4 (C) ACTIVE & REACTIVE PoWERS

FIG. 4 (D) FREQUENCY VARIATIoN

From the Figure [4(a)–4(d)], the variation of HES generation of PV & wind HES is studied. From Figure 4(a) it can be realized that, the DC Link voltage is constant throughout the simulation after it reaches steady state value irrespective of variation of generation. In Figure 4(b), load current & system voltages are constant, the increase in PV & wind current due to increase in irradiation at 1.25s, is shared to grid as shown. In Figure 4(c), PV & wind reactive power is decreased at 0.9s due to decrease in temperature &PV & wind active power is increased at 1.25s due to increase in irradiation. The Figure 4(d) shows the system frequency variation throughout the simulation time & it is within the limit of grid connection requirement, which is specified in the standard IEEE-1547.

5.0 CONCLUSIONS

The performances of modeled system are meeting the RES grid interconnection requirements which are specified in IEEE 1547, under generation variation of HES with grid interface.

6.0 ACKNOWLEDGEMENT

Authors would like to extend the gratitude to EEE dept. faculties of NITK Surathkal, Karnataka and EEE dept. faculties of SET, Jain University, Karnataka.

Authors would like to extend special thanks to Mr. Mohan Krishna S, Research scholar, VIT and Santhosha Kumar A, Research scholar, NITK Surathkal.

REFERENCES

[1] B. M Hasaneen and Adel A. Elbaset Mohammed, “Design and Simulation of DC/DC Boost Converter”, IEEE, 2008.

[2] Chen Wang, Liming Wang, Libao Shi and Yixin Ni, “A Survey on Wind Power Technologies in Power Systems”, IEEE, 2007.

[3] Fei Ding, Peng Li, Bibin Huang, Fei Gao, Chengdi Ding and Chengshan

506 The Journal of CPRI, Vol. 10, No. 3, September 2014

Wang, “Modeling and Simulation of Grid-connected Hybrid Photovoltaic/Battery Distributed Generation System”, China International Conference on Electricity Distribution, 2010.

[4] IEEE 1547 “IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems”. IEEE Standards Coordinating Committee 21 on Fuel Cells, Photovoltaics, Dispersed Generation, and Energy Storage, 2008.

[5] KiamHeongAng, Gregory Chong and Yun Li, “PID Control System Analysis, Design, and Technology”, IEEE Transactions on Control Systems Technology, vol. 13, no. 4, 2005.

[6] M. G. Villalva, J. R. Gazoli, E and Ruppert F, “Modeling and Circuit-Based Simulation of Photovoltaic Arrays”, Brazilian Journal of Power Electronics Vol. 14, no. 1, pp. 35-45, 2009.

[7] Santhosha Kumar A, “Modeling and simulation of fuel cell based distributed generation system”, Project report submitted in electrical and electronics department at national institute of technology Karnataka, Chapter 3, 30-33, 2010.

[8] Vechiu, A. Llaria, o. Curea and H. Camblong, “Control of Power Converters for Microgrids”, MoNACo, 2009.

[9] Yaow-Ming Chen, Chung-Sheng Cheng, and Hsu-Chin Wu, “Grid-Connected Hybrid PV/Wind Power Generation System with Improved DC Bus Voltage Regulation Strategy”, IEEE, 2006.

[10] Nagendra K, Dr. Vinatha U and Dr. N Krishnamurthy, “Simulation and performance study of grid-connected wind and photovoltaic hybrid energy system”, CPRI June 2014.