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A NOVEL HIGH PERFORMANCE DUAL CONTROL STRATEGY FOR ISLANDING OPERATIONS WITH PV GENERATION USING FUZZY Ch. naga sai kalyan1, M. seshu2 II year M.Tech, power systems and automation, PVPSIT, vijayawada, India 1 Assistant Professor of Electrical Engineering, PVPSIT, vijayawada, India 2 Abstract-The Distributed Generation (DG) technologies, which include both conventional and non-conventional type of energy sources for generating power, are gaining momentum and play major role in distribution system. This paper presents a high performance fuzzy based dual control strategy that enables both islanded and grid-tied operations of three-phase inverter in distributed generation, with no need for switching between two corresponding controllers or critical islanding detection. The proposed control strategy composes of an inner inductor current loop, and a novel voltage loop in the synchronous reference frame. The inverter is regulated as a current source just by the inner inductor current loop in grid-tied operation, and the voltage controller is automatically activated to regulate the load voltage upon the occurrence of islanding .The waveforms of the grid current in the grid-tied mode and the load voltage in the islanding mode are distorted under nonlinear local load with the conventional strategy. so, in this paper i want to propose a high performance fuzzy based dual control method for islanding operations and the effectiveness of the control method is validated by using simulation results. Key words: Distributed generation (DG), Feed forward, Islanding, Total harmonic distortion (THD). 1.INTRODUCTION The Renewable Energy Source (RES) integrated at distribution level is termed as Distributed Generation (DG). DG is emerging as a viable alternative when renewable or nonconventional energy resources are available, such as wind turbines, photovoltaic arrays, fuel cells, microturbines [1], [3]. Most of these resources are connected to the utility through power electronic interfacing converters, i.e., three-phase inverter. Moreover, DG is a suitable form to offer high reliable electrical power supply, as it is able to operate either in the gridtied mode or in the islanded mode [2]. In the grid-tied operation, DG deliveries power to the utility and the local critical load. Upon the occurrence of utility outage, the islanding is formed. Under this circumstance, the DG must be tripped and cease to energize the portion of utility as soon as possible. However, in order to improve the power reliability of some local critical load, the DG should disconnect to the utility and continue to feed the local critical load [5]. The load voltage is key issue of these two operation modes, because it is fixed by the utility in the grid-tied operation, and formed by the DG in the islanded mode, respectively. Therefore, upon the happening of islanding, DG must take over the load voltage as soon as possible, in order to reduce the transient in the load voltage. 2.SYSTEM DESCRIPTION Fig1: Schematic diagram of DG based on proposed control strategy. This paper presents a high performance fuzzy based dual control strategy for a three phase inverter in DG to operate in both islanded and grid-tied modes. The schematic diagram of the DG based on the proposed control strategy is shown by Fig. 1. The DG is equipped with a three-phase interface inverter terminated with a LC filter. The primary energy is converted to the electrical energy, which is then converted to dc by the front-end power converter, and the output dc voltage is regulated by it. In the ac side of inverter, the local critical load is connected directly. It should be noted that there are two switches, denoted by Su and Si, respectively, in Fig.1, and their functions are different. The inverter transfer switch Si is controlled by the DG, and the utility protection switch Su is governed by the utility. When the utility is normal, both switches Si and Su are ON, and the DG in the grid-tied mode injects power to the utility. When the utility is in fault, the switch Su is tripped by the utility instantly, and then the islanding is formed. After the islanding has been confirmed by the DG with the islanding detection scheme [6]–[10], the switch Si is disconnected, and the DG is transferred from the grid-tied mode to the islanded mode. When the utility is restored, the DG should be resynchronized with the utility first, and then the switch Si is turned ON to connect the DG with the grid. 3.RELATED WORK 3.1. HARMONIC DISTORTION Harmonic problems are almost always introduced by the consumers’ equipment and installation practices. Harmonic distortion is caused by the high use of nonlinear load equipment such as computer power supplies, electronic ballasts, compact fluorescent lamps and variable speed drives etc., which create high current flow with harmonic frequency components. The limiting rating for most electrical circuit elements is determined by the amount of heat that can be dissipated to avoid overheating of bus bars, circuit breakers, neutral conductors, transformer windings or generator alternators. Ratio of the square root of the sum of squares of the rms value of harmonic component to the rms value of the fundamental components defined as Total Harmonic Distortion (THD) If the waveform under discussion is current, then the THD definition is called Current Harmonic Distortion. 3.2. PV GENERATION Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into a flow of electrons. The photovoltaic effect refers to photons of light exciting electrons into a higher state of energy, allowing them to act as charge carriers for an electric current. Fig2: Schematic diagram of PV generation 4.PROPOSED STRATEGY Fig3: Simulink diagram of proposed control strategy 4.1. Fuzzy logic controller The disadvantage of PI controller is its inability to react to abrupt changes in the error signal, ε, because it is only capable of determining the instantaneous value of the error signal without considering the change of the rise and fall of the error, which in mathematical terms is the derivative of the error denoted as Δε. To solve this problem, [11][12] Fuzzy logic control as it is shown in Fig 4 is proposed. T he determination of the output control signal, is done in an inference engine with a rule base having if-then rules in the form of "IF ε is ....... AND Δε is ......., THEN output is ........" With the rule base, the value of the output is changed according to the value of the error signal ε, and the rate-of- error Δε. The structure and determination of the rule base is done using trial-and-error methods and is also done through experimentation TABLE-1 FUZZY LOGIC CONTROL RULES ε NL NM NS EZ PS PM PL NL NM NS EZ PS PM PL NL NL NL NL NM NS EZ NL NL NM NM NS EZ PS NL NM NS NS EZ PS PM NL NM NS EZ PS PM PL NM NS EZ PS PS PM PL NS EZ PS PM PM PL PL EZ PS PM PL PL PL PL Fig4: member ship function plots 5.SIMULATION RESULTS An extensive simulation study is carried out using MATLAB/Simulink in order to verify the proposed control strategy. Fig5: simulation wave forms of a. load voltage, b.grid current c.inductor current When DG is in grid tied mode. Fig6: simulation wave forms of a. load voltage, b.grid current c.inductor current When DG is transferred from grid tied to islanding mode. Fig7: simulation wave forms of a. load voltage, b.grid current c.inductor current When DG is in islanding mode (conventional method) Fig8: simulation wave forms of a. load voltage, b.inductor current c. current at load, d.grid current When DG is in islanding mode using proposed fuzzy control Strategy. 5.CONCLUSION The proposed control strategy for three-phase inverter in dg to operate in both islanded and grid tied mode, a novel voltage controller was inactivated in the grid tied mode, and the dg operates as a current source with fast dynamic performance. Upon the utility outage, the voltage controller can automatically be activated to regulate the load voltage. The proposed unified control strategy was verified by the simulation results. The total harmonic distortion in the islanding mode when using PI controller is 1.74% and it comes down when fuzzy logic is used, it is about 1.59%. REFERENCES [1] R. C. Dugan and T. E. McDermott, “Distributed generation,” IEEE Ind. Appl. Mag., vol. 8, no. 2, pp. 19–25, Mar./Apr. 2002. [2] R. H. Lasseter, “Microgrids and distributed generation,” J. Energy Eng., vol. 133, no. 3, pp. 144–149, Sep. 2007. [3] C. Mozina, “Impact of green power distributed generation,” IEEE Ind. Appl. Mag., vol. 16, no. 4, pp. 55–62, Jul./Aug. 2010. [4] IEEE Recommended Practice for Utility Interface of Photovoltaic(PV) Systems, IEEE Standard 929-2000, 2000. [5] IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, IEEE Standard 1547-2003, 2003. [6] J. Stevens, R. Bonn, J. Ginn, and S. Gonzalez, Development and Testing of an Approach to Anti-Islanding in Utility-Interconnected Photovoltaic Systems. Livermore, CA, USA: Sandia National Laboratories, 2000. [7] A. M. Massoud, K. H. Ahmed, S. J. Finney, and B. W. Williams, “Harmonic distortionbased island detection technique for inverter-based distributed generation,” IET Renewable Power Gener., vol. 3, no. 4, pp. 493– 507, Dec. 2009. [8] T. Thacker, R. Burgos, F. Wang, and D. Boroyevich, “Single-phase islanding detection based on phase-locked loop stability,” in Proc. 1st IEEE Energy Convers. Congr. Expo., San Jose, CA, USA, 2009, pp. 3371–3377. [9] S.-K. Kim, J.-H. Jeon, J.-B. Ahn, B. Lee, and S.-H. Kwon, “Frequencyshift acceleration control for anti-islanding of a distributed-generation inverter,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 494–504, Feb. 2010. [10] A. Yafaoui, B. Wu, and S. Kouro, “Improved active frequency drift antiislanding detection method for grid connected photovoltaic systems,” IEEE Trans. Power Electron., vol. 27, no. 5, pp. 2367–2375, May 2012. [11] Rachid Dehini, Brahim Ferdi "STATCOM Dc-bus Voltage ControllerBased on Fuzzy logic" IJAEST vol.11.,pp.281-285. [12] M.Bhanu Siva, M.R.P Reddy, Ch.Rambabu "Power Quality Improvement of Threephase four-wire DSTATCOM with Fuzzy logic Controller" ICSIT.,vol.2,pp. 22732273.,2011.