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ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 1, July 2012 Real Time Simulation of Solar Powered Cascaded Multilevel Inverter Shimi S.L, Dr. Thilak Thakur, Dr. Jagadeesh, Dr.S.Chatterji Abstract— This paper deals with the design and simulation of solar powered cascaded H-bridge multilevel inverter. The Pulse Width Modulated (PWM) technique of switching pattern is used to to improve the power quality of the supply voltage and current and thus to reduce the Total Harmonic Distortion (THD) . A detailed simulation has been carried out for the 11 level inverter and the validation of the system is verified through MATLAB/SIMULINK and the results in terms of THD are simulated. Index Terms—Total Harmonic Distortion (THD), Solar Powered Multilevel Inverter. problem. The methods to solve such polynomial equations using elimination theory are discussed in [8]. The solar powered multilevel inverter introduces a lot of harmonics. In this paper a PWM algorithm is used for the elimination the higher order harmonics. To eliminate the low order harmonics like 5th, 7th, 11th and 13th the fundamental frequency switching scheme can be used. The knowledge of harmonic elimination for multilevel inverter is very necessary as it gives an idea about the switching pattern for harmonic elimination in case of 11 level cascade multilevel inverter [9]. II. MULTILEVEL INVERTER DRIVES (MLIDS) I. INTRODUCTION The industry has begun to stipulate higher power ratings. The medium voltage applications require medium voltage and megawatt power level. The solution for such an application is the multilevel power converter structure. The investigators in [1] have discussed the two topologies of multilevel inverters for electric drive application. The high VA rating of cascade multilevel inverter makes it fit for large automotive electric drives and it uses several dc voltage sources which would be available from batteries or fuel cells [2]. One of the advantage of multilevel inverter is that it enables the interface of renewable energy sources such as photovoltaic, wind, and fuel cells in the dc input portion of the multilevel inverter and can be used for a high power application [1, 2]. Multilevel converters have received more and more attention because of their capability of high voltage operation, high efficiency, and low electromagnetic interference (EMI) [3][1]. The multilevel inverters use large number of power semiconductor devices for their switching thus results in more switching losses and is less reliable. But the industrial applications such as industrial manufacturing are more dependent on induction motors and their inverter systems for process control. The IEEE 519 standard limits of THD of the output voltage of the converter circuit should be maintained for such applications [4]. In industries the harmonics mitigation of multilevel inverter circuit is a very important issue. In [5-7] the investigators have proposed the elimination theory to determine the switching patterns to eliminate the specific harmonics, such as 5th, 7th, 11th, and the 13th. In case of 3 phase 11 level multilevel inverter there are 15 dc sources, as the number of dc sources increases the degrees of the polynomials in these equations increases and thus it becomes difficult to solve such a In industrial drives the conventional inverter drives are most commonly used. They consist of six power switches with pulse width modulation (PWM) switching. By using such conventional converters the output voltage and current waveform qualities has deteriorated. To overcome this problem and improve the waveform quality the switching frequency should be increased, but these results in higher switching losses. Compared to the conventional two level inverters the multilevel inverters have a number of advantages from which some of them are listed below. (i) As the number of levels of multilevel inverter is increased the output staircase waveform is more close to a sine wave thus very low distortion is produced in the output. (ii) The dv/dt stress is reduced. (iii) The stress in the motor bearings connected to a multilevel motor drive is small as the commonmode (CM) voltage produced in the multilevel inverters is very small. [10] (iv) Low distortion input current. (v) Multilevel inverter can work at both low and high switching frequencies. The investigator of [1] has mainly discussed two topologies of multilevel inverters for electric drive application [1]. (a) The cascade MLID (b) The back-to-back diode-clamped converter The cascaded MLID is the main focus of this paper. The Fig. 1 shows the single-phase structure of a m-level cascaded inverter. 179 ……(1) ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 1, July 2012 Rs I + Rs V H _ Fig. 2 Single Diode Model of a PV Cell In literature a number of approaches and models can be found to analyze the behavior of PVs [12-14]. The PV cell model used in this work is based on the single diode cell . The VI characteristics (in green) of a typical solar cell are as shown in the 3 Fig. 3. 1 . PMPP 14 . 21 Cell current in A IMP P MP P 2 . 25 1 . 5 1 0 . 05 Cell voltage in V V oc 0 . 80 . 60 . 40 . 20 0 0 0 0 0 0 0 0 . . . . . . . 1 2 3 Curve 4 of 5Photovoltaic 6 7 Cell Fig. 3 V-I and P-V Characteristics When the voltage and the current characteristics are multiplied we get the P-V characteristics (in blue) as shown in Fig. 4. The point highlighted as MPP is the point at which the panel power output is maximum [15]. The equation (2) is the basic equation for the photovoltaic current. Fig. 1 Single-Phase Structure of a M-Level Cascaded Inverter III. PV MODELING Modeling of a solar cell is done by connecting a current source in parallel with an inverted diode along with a series and a parallel resistance as shown in Fig.2. The series resistance is due to hindrance in the path of flow of electrons from n to p junction and parallel resistance is due to the leakage current. The single diode model shown in Fig. 2 [11] was adopted for simulating the PV module under different irradiance and temperature levels. The modeling of the PV cell was done in MATLAB/SIMULINK by writing the code in the embedded block. The PV cell subsystems were modeled and connected to the 11 level cascade multilevel inverter. …………………(2) Where, Ipv : photovoltaic current I0 : saturation current Vt : thermal voltage Rs : equivalent series resistance Rp : equivalent parallel resistance a: diode ideality constant IV. PROPOSED DESIGN In this proposed method of the solar powered 11 level cascade inverter, has five input stages, all the five stages are alike in the construction module. All the modules are 180 Cell power in W . 3 5 ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 1, July 2012 connected as new hybrid with each module having power the FFT analysis tool and is shown in Fig.6 . The total switches. The IGBT, MOSFET or any other power devices harmonic distortion is found to be 8.50 %. can be used as the power switches in these modules. The GTO’s are used in this system. Fig. 5. Inverter Output Voltage Fig. 4. Three-Phase Wye-Connection Structure for Solar Powered 11 Level Cascade Inverter In the switching mode of the power switches any two switches are in operating conditions at a time and the other two power switches remain in open condition. To attain +Va, the switches S1 and S4 of Fig. 4 are turned on, whereas to attain -Va switches S2 and S3 are turned on. If power switches S1 and S2 or S3 and S4 are on , the output voltage is 0, this method is adopted to protect the circuit from short circuiting . Each H bridge module is connected with a PV cell as shown in Fig. 4. V. SIMULATED CIRCUITS AND WAVEFORMS Figure 7. Shows the MATLAB/SIMULINK diagram of the proposed three-phase wye-connection structure for solar powered 11 level cascade multilevel inverter fed induction motor. The subsystem of the solar powered 11 level cascade multilevel inverter is shown in Fig 8. The Inverter’s phase voltage and line voltage during simulation are shown in Fig. 5. The FFT spectrum of the line voltage is found using Fig. 6. FFT Spectrum 181 ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 1, July 2012 Fig 7 Simulation Diagram Of Proposed System Fig 8. Subsystem of the Solar Powered 11 Level Cascades Multilevel Inverter VIII. CONCLUSION A three-phase solar powered 11 level cascade inverter has been proposed, and its principle of operation has been conﬁrmed by simulation results. The PV cell modeling was performed and the dc supply for all the H-bridges were supplied through the PV cells. PWM switching pattern is used to fire the GTOs of multilevel inverter for reducing the Total Harmonic Distortion (THD) and to improve the power quality of the supply voltage and current. The total harmonic distortion is found to be 8.50 % for the proposed model. Using the optimization and artificial intelligent techniques and fractional order controllers in this proposed model the THD can still be minimized. REFERENCES [1] L.M. Tolbert, F. Z. Peng, T. G. Habetler, “Multilevel converters for large electric drives, ” IEEE Transactions on Industry Applications, vol. 35, no. 1, Jan./Feb. 1999, pp. 3644. [2] J. Rodriguez, J. S. Lai, and F. Z. Peng, “Multilevel Inverters: Survey of Topologies, Controls, and Applications,” IEEE 182 ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 1, July 2012 Transactions on Industry Applications, vol. 49, no. 4, Aug. 2002, pp. 724-738. Engineering and Technology Research Center, Vol No. 1, Issue No. 1, pp 043-049, 2011. [3] J. S. Lai and F. Z. Peng, “Multilevel converters – A new breed of power converters,” IEEE Transactions on Industry Applications, vol. 32, no. 3, May /June 1996, pp. 509-517. [10] E. Cengelci, S. U. Sulistijo, B. O. Woom, P. Enjeti, R. Teodorescu, and F. Blaabjerg, “A New Medium Voltage PWM Inverter Topology for Adjustable Speed Drives,” in Conf. Rec. IEEE-IAS Annual Meeting, St. Louis, MO, Oct. 1998, pp. 1416-1423. [4] C. K. Duffey and R. P. Stratford, “Update of harmonic standard IEEE-519: IEEE recommended practices and requirements for harmonic control in electric power systems,” IEEE Transactions on Industry Applications, vol. 25, no. 6, Nov./Dec. 1989, pp. 1025-1034. [5] H. S. Patel and R. G. Hoft, “Generalized harmonic elimination and voltage control in thyristor inverters: Part I – harmonic elimination,” IEEE Transactions on Industry Applications, vol. 9, May/June 1973, pp. 310-317. [6] H. S. Patel and R. G. Hoft, “Generalized harmonic elimination and voltage control in thyristor inverters: Part II – voltage control technique,” IEEE Transactions on Industry Applications, vol. 10, Sept./Oct. 1974, pp. 666-673. [7] P. N. Enjeti, P. D. Ziogas, J. F. Lindsay, “Programmed PWM techniques to eliminate harmonics: A critical evaluation” IEEE Transactions on Industry Applications, vol. 26, no. 2, March/April. 1990. pp. 302 – 316. [8] J. N. Chiasson, L. M. Tolbert, K. J. McKenzie, Z. Du, “A new approach to solving the harmonic elimination equations for a multilevel converter,” IEEE Industry Applications Society Annual Meeting, October 12-16, 2003, Salt Lake City, Utah, pp. 640-645. [11] F. Filho, L. M. Tolbert, B. Ozpineci, Y. Cao, "Real Time Selective Harmonic Minimization for Multilevel Inverters Connected to Solar Panels Using Artificial Neural Network Angle Generation," IEEE Transactions on Industry Applications, vol. 47, no. 5, Sept.-Oct. 2011, pp. 2117-2124 [12] U. Boke, “A simple model of photovoltaic module electric characteristics,” European Conference on Power Electronics and Applications, pp.1-8,Sept. 2007. [13] O. Gil-Arias, E. I. Ortiz-Rivera, “A general purpose tool for simulating the behavior of PV solar cells, modules and arrays,” 11th Workshop on Control and Modeling for Power Electronics, pp. 1-5, Aug. 2008. [14] R. Ramaprabha, B. L. Mathur, “MATLAB based modeling to study the influence of shading on series connected SPVA,” 2nd International Conference on Emerging Trends in Engineering and Technology, pp. 30-34, Dec. 2009. [15] Marcelo G, Gazoli J. and Filho E., “Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays”, IEEE Transactions On Power Electronics, vol. 24, no. 5, May 2009, p.p.1198-1208. [9] T. Sripal Reddy, Dr. B.V.Sanker Ram, Dr. K. Raghu Ram “The Simulation And Analysis Of Multilevel Inverter Fed Induction Motor Drive”, International Institute of 183