ISSN Vol.05,Issue.01, January-2017, Pages:

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1 ISSN Vol.05,Issue.01, January-2017, Pages: Fuzzy Logic Modular Cascaded H-Bridge Multi Level Inverter with Distributed MPPT Grid Interconnection PVA KOLA ARAVINDA 1, K. VAMSEE KRISHNA 2 1 PG Scholar, Dept of EEE, Vignana Bharthi Institute of Technology, Ghatkesar, TS, India, aravindakola@gmail.com. 2 Associate Professor, Dept of EEE, Vignana Bharthi Institute of Technology, Ghatkesar, TS, India, kvkvbit@gmail.com. Abstract: The modular cascaded H-bridge inverters are in verge of increasing utilization in modern day technology. The modular cascaded H-bridge inverters reduce the THD in the output voltage of the converter with DC renewable input sources. In this paper we introduce a new control topology which operates as a MPPT booster converter and also multi level inverter. As compared to conventional grid connected converters, reduction in switching states and also reduction in switching losses is achieved with the proposed topology. The control topology is modeled with fuzzy controllers to decrease the reaction time of the converter with change in solar irradiation. Multiple PVA panels are used as input sources to the cascaded H-bridge converter. The output voltage THD and power exchange are observed using MATLAB software with all graphical representations. is causing global warming. Due to this the efficiency of the PVA has to be increased by adding silicon surface on the panel. And also employ MPPT techniques to track maximum power during any irradiation and atmospheric conditions. The design of PVA is done in MATLAB with Simulink block, with mathematical representation. Keywords: Photovoltaic (PV), THD, PVA (Photo Voltaic Array), Fuzzy Controllers. I. INTRODUCTION Recently, the multilevel converter is emerging as a new breed of power converter option for high power applications, which can create high voltage and reduce harmonics by its own circuit topology as shown in Fig.1. From the research on it before, it is shown that the multi level converter bas better performance than conventional converter in output harmonics spectra, efficiency, stress on devices and power factor etc. There are three reported basic topologies of multilevel converter: 1)Diode lamp; 2) Flying Capacitors; 3) Cascade- Inverter with separated DC Sources (CISDCS) comparatively, CISDCS has many dominant advantages The structure based on conventional two level full bridge inverter units, so the topology is very simple. Modularized circuit layout and packaging is possible because each level has the same structure, and there are no extra clamping diodes or voltage balancing capacitors. There is no neutral point voltage unbalance problem, for each bridge is fed with a separated DC sources. Fig. 1. Cascaded H-bridge. Voltage of PVA completely depends on solar irradiation (Sx) and ambient temperature (Tx). PVA (Photo voltaic array) is a combination of series and parallel solar cells arranged in an array to generated the required voltage and current. Each series combination of cells can be considered as photo voltaic module. Increase in series cells increases the voltage and increase in parallel cells increases the current capacity. Formulation for voltage of each cell is given below II. PVA AND MPPT MODELING For efficient renewable power generation PVA is used to generate power from solar irradiation. As the load demand is increasing day by day the power generation also has to be increased, but due to the traditional way of power generation Where, k = Boltzmann constant ( J/oK). I c = cell output current, Amp. I ph = photocurrent (1) 2017 IJIT. All rights reserved.

2 I 0 = reverse saturation current of diode R s = series resistance of cell T c = reference cell operating temperature V c = cell voltage, V. The Boltzmann constant and the reference temperature have to be in same units ie., either 0 C or 0 K. The mathematical modeling of the above equation can be constructed using simulink blocks is as below Fig.2. KOLA ARAVINDA, K. VAMSEE KRISHNA The correction factors are given as (3) (4) Where, β T = and T = 0.06 T a = reference temperature T x = ambient temperature S c = reference solar irradiation S x = ambient solar irradiation (5) Fig. 2. Simulink model of Vc. The above design is for a single cell voltage, in order to increase the voltage of the PVA the cell voltage has to be multiplied to a desired values considering each cell voltage as 0.4V. So, the number of series connected cells (N s ) can be calculated as The values of Tx and Sx changes depending upon the Sun rays which change continuously and unpredictably. The effect of change in solar irradiation varies the cell photocurrent and also the cell voltage (Vc). Let us consider the initial solar irradiation is I sx1 & the increase of the irradiation is I sx2 which in turn increases the temperature from T x1 to T x2, photocurrent from I phx1 to I phx2. The mathematical modeling of the correction factors in simulink is given below Fig.4. (2) To get each cell current, the total current output from the dependable source has to be divided by number of parallel connected cells (N p ) as shown in Fig.3. Therefore, parallel connected cells are considered as The representation in simulink is taken as (2) Fig. 4. CI & CV modeling. Depending upon the solar irradiation and temperature the values of CV & CI are calculated which is fed to Vc block to get the cell voltage value as shown below Fig.5. Fig. 3. Simulink modeling of Ns &Np. For the calculation of Vcx (cell voltage) and Iphx (Photocurrent) we need correction factors C TV C TI C SV C SI. Fig. 5. Combined diagram of CV CI &Vc mathematical The formulation is given as models.

3 Fuzzy Logic Modular Cascaded H-Bridge Multi Level Inverter with Distributed MPPT Grid Interconnection PVA The total system diagram of the PVA with all the mathematical formulation are put into a subsystem to make it clear and understandable. The output of the Vc multiplied with the Ns constant block defining the total voltage of the combined cells of the PVA is fed to the voltage controlled voltage source block so as to generate the required voltage. A diode is connected in series at the positive terminal of the PVA to avoid reverse currents passing into the PVA. To reduce the ripples a capacitor can be added later after the diode in parallel as the capacitor doesn t allow sudden change of voltages dv/dt. The complete PVA module with internal block construction is shown in the fig. 6 below module in phase a. After multiplied by the modulation index of phase a, n 1 modulation indices can be obtained. Also, the modulation index for the first H-bridge can be obtained by subtraction. The control schemes in phases b and c are almost the same. The only difference is that all dc-link voltages are regulated through PI controllers, and n modulation index proportions are obtained for each phase. A phase-shifted sinusoidal pulse width modulation switching scheme is then applied to control the switching devices of each H-bridge. Fig. 6. Complete diagram of PVA. A. Distributed MPPT Control In order to eliminate the adverse effect of the mismatches and increase the efficiency of the PV system, the PV modules need to operate at different voltages to improve the utilization per PV module. The separate dc links in the cascaded H- bridge multilevel inverter make independent voltage control possible. To realize individual MPPT control in each PV module, the control scheme proposed is updated for this application. The distributed MPPT control of the three-phase cascaded H-bridge inverter is shown in Fig. 7. In each H- bridge module, an MPPT controller is added to generate the dc-link voltage reference. Each dc-link voltage is compared to the corresponding voltage reference, and the sum of all errors is controlled through a total voltage controller that determines the current reference Idref. The reactive current reference Iqref can be set to zero, or if reactive power compensation is required, Iqref can also be given by a reactive current calculator. The synchronous reference frame phase-locked loop (PLL) has been used to find the phase angle of the grid voltage. As the classic control scheme in three-phase systems, the grid currents in abc coordinates are converted to dq coordinates and regulated through proportional integral (PI) controllers to generate the modulation index in the dq coordinates, which is then converted back to three phases. The distributed MPPT control scheme for the single-phase system is nearly the same. The total voltage controller gives the magnitude of the active current reference, and a PLL provides the frequency and phase angle of the active current reference. The current loop then gives the modulation index. To make each PV module operate at its own MPP, take phase a as an example; the voltages vdca2 to vd can are controlled individually through n 1 loops. Each voltage controller gives the modulation index proportion of one H-bridge Fig. 7. Three phase H-bridge inverter. It can be seen that there is one H-bridge module out of N modules whose modulation index is obtained by subtraction. For single-phase systems, N = n, and for three-phase systems, N =3n, where n is the number of H-bridge modules per phase. The reason is that N voltage loops are necessary to manage different voltage levels on N H-bridges, and one is the total voltage loop, which gives the current reference. So, only N 1 modulation indices can be determined by the last N 1 voltage loops, and one modulation index has to be obtained by subtraction. Many MPPT methods have been developed and implemented N. The incremental conductance method has been used in this paper as shown in Fig.8. It lends itself well to digital control, which can easily keep track of previous values of voltage and current and make all decisions. Fig. 8. Cascaded H-bridge inverter Control structure with MPPT algorithm.

4 KOLA ARAVINDA, K. VAMSEE KRISHNA Fig. 12.Linearization rules. Fig. 9. Modulation compensation structure. As mentioned earlier, a PV mismatch may cause more problems to a three-phase modular cascaded H-bridge multilevel PV inverter. With the individual MPPT control in each H-bridge module, the input solar power of each phase would be different, which introduces unbalanced current to the grid. To solve the issue, a zero sequence voltage can be imposed upon the phase legs in order to affect the current flowing into each phase. If the updated inverter output phase voltage is proportional to the unbalanced power, the current will be balanced. Thus, the modulation compensation block, as shown in Fig. 9, is added to the control system of threephase modular cascaded multilevel PV inverters. The key is how to update the modulation index of each phase without increasing the complexity of the control system. First, the unbalanced power is weighted by ratio r. As it can be seen in the above figs.10 to 12 the output generates the nearest value of the modulation index which is integrated to the PWM generator generating optimal power outputs for a change in the system parameters or devices. IV. SIMULINK RESULTS AND OUTPUTS Simulation results of this paper is as shown in bellow Figs.13 to 17. Fig. 13. Simulink system with Cascaded PVA connected to grid. III. FUZZY CONTROL A fuzzy control is basically used to make the system react faster and get nearest values and making the system more reliable. In our paper we are considering seven input and output membership functions. The output of the fuzzy follow linearization rule. The memebership functions with rule table is given below. Fig. 14. Integration of fuzzy in control structure. Fig. 10. Input membership functions. Fig. 15. Voltage output of each PVA. Fig. 11.Output membership functions. Fig. 16.Total power output of PVA.

5 Fuzzy Logic Modular Cascaded H-Bridge Multi Level Inverter with Distributed MPPT Grid Interconnection PVA Fig. 17.Comparison of Active and reactive powers of PI and fuzzy control. V. CONCLUSION With the above results and discussion on implementation of fuzzy in modular cascaded H-bridge inverter control structure the power quality is improvised. The comparison of Active and reactive powers are shown with respect to the injection of powers from PVA to grid. The reaction time of the injected power by fuzzy are more responsive and reliable as compared to PVA control. VI. REFERENCES [1] J. M. Carrasco et al., Power-electronic systems for the grid integration of renewable energy sources: A survey, IEEE Trans. Ind. Electron., vol. 53, no. 4, pp , Jun [2] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, A review of single-phase grid connected inverters for photovoltaic modules, IEEE Trans. Ind. Appl., vol. 41, no. 5, pp , Sep./Oct [3] M. Meinhardt and G. Cramer, Past, present and future of grid connected photovoltaic- and hybrid power-systems, in Proc. IEEE PES Summer Meet., 2000, vol. 2, pp [4] M. Calais, J. Myrzik, T. Spooner, and V. G. Agelidis, Inverter for single-phase grid connected photovoltaic systems An overview, in Proc. IEEE PESC, 2002, vol. 2, pp [5] J. M. A. Myrzik and M. Calais, String and module integrated inverters for single-phase grid connected photovoltaic systems A review, in Proc. IEEE Bologna Power Tech Conf., 2003, vol. 2, pp [6] F. Schimpf and L. Norum, Grid connected converters for photovoltaic, state of the art, ideas for improvement of transformerless inverters, in Proc. NORPIE, Espoo, Finland, Jun. 2008, pp [7] B. Liu, S. Duan, and T. Cai, Photovoltaic DC-buildingmodule-based BIPV system Concept and design considerations, IEEE Trans. Power Electron., vol. 26, no. 5, pp , May [8] L. M. Tolbert and F. Z. Peng, Multilevel converters as a utility interface for renewable energy systems, in Proc. IEEE Power Eng. Soc. Summer Meet., Seattle, WA, USA, Jul. 2000, pp [9] H. Ertl, J. Kolar, and F. Zach, A novel multicell DC AC converter for applications in renewable energy systems, IEEE Trans. Ind. Electron., vol. 49, no. 5, pp , Oct [10] S. Daher, J. Schmid, and F. L. M. Antunes, Multilevel inverter topologies for stand-alone PV systems, IEEE Trans. Ind. Electron., vol. 55, no. 7, pp , Jul [11] G. R. Walker and P. C. Sernia, Cascaded DC DC converter connection of photovoltaic modules, IEEE Trans. Power Electron., vol. 19, no. 4, pp , Jul [12] E. Roman, R. Alonso, P. Ibanez, S. Elorduizapatarietxe, and D. Goitia, Intelligent PV module for grid-connected PV systems, IEEE Trans. Ind. Electron., vol. 53, no. 4, pp , Jun [13] F. Filho, Y. Cao, and L. M. Tolbert, 11-level cascaded H-bridge grid-tied inverter interface with solar panels, in Proc. IEEE APEC Expo., Feb. 2010, pp [14] C. D. Townsend, T. J. Summers, and R. E. Betz, Control and modulation scheme for a cascaded H-bridge multi-level converter in large scale photovoltaic systems, in Proc. IEEE ECCE, Sep. 2012, pp [15] B. Xiao, L. Hang, and L. M. Tolbert, Control of threephase cascaded voltage source inverter for grid-connected photovoltaic systems, in Proc. IEEE APEC Expo., Mar. 2013, pp