SINGLE PHASE THIRTY ONE LEVEL INVERTER USING EIGHT SWITCHES TOWARDS THD REDUCTION

Transcription

1 SINGLE PHASE THIRTY ONE LEVEL INVERTER USING EIGHT SWITCHES TOWARDS THD REDUCTION T.Ramachandran 1, P. Ebby Darney 2 and T. Sreedhar 3 1 Assistant Professor, Dept of EEE, U.P, Subharti Institute of Technology and Engineering 2 Head of the Department of EEE, Tirunelveli, Scad College of Engineering & Technology 3 Executive Director, Tirunelveli,Nice Panel Electrical & Automation Abstract This project proposes a single-phase thirty one level inverter with reduced switches, with a novel pulse width-modulated (PWM) control scheme. The Proposed multilevel inverter output voltage level increasing by using eight numbers of switches driven by the multicarrier modulation techniques. The inverter is capable of producing thirty one levels of output-voltage (Vdc, 14Vdc/15, 13Vdc/15, 12Vdc/15, 11Vdc/15, 10Vdc/15, 9Vdc/15, 8Vdc/15, 7Vdc/15, 6Vdc/15, 5Vdc/15, 4Vdc/15, 3Vdc/15, 2Vdc/15, Vdc/15,0, -Vdc/15,- 2Vdc/15,- 3Vdc/15,- 4Vdc/15,- 5Vdc/15,- 6Vdc/15,- 7Vdc/15,- 8Vdc/15,-) 9Vdc/15,- 10Vdc/15,- 11Vdc/15,- 12Vdc/15,- 13Vdc/15,- 14Vdc/15,- Vdc) from the dc supply voltage. This topology achieves very less THD with less number of switches. The proposed system was verified through MATLAB simulation. Keywords Multi Carrier, THD, PWM, Symmetrical, MLI. I. INTRODUCTION Multilevel inverters are promising; they have nearly sinusoidal output-voltage waveforms, Output current with better harmonic profile, less stressing of electronic components owing to decreased voltages, switching losses that are lower than those of conventional two-level inverters, a smaller filter size, and lower EMI, all of which make them cheaper, lighter, and more compact. Various topologies for multilevel inverters have been proposed over the years. Common ones are diode-clamped, flying capacitor or multi cell, cascaded H-bridge, and modified H-bridge multilevel. This paper recounts the development of one novel modified H-bridge single-phase multilevel inverter that has one diode embedded bidirectional switches and a novel pulse width modulated (PWM) technique. Multilevel inverter is the generation of high voltage using lower voltage rating devices connected in series. Also it has the potential to get a high quality output voltage by producing multi output voltage levels. However it increases the number of switching devices and other components, which result in an increase of complexity problems and systems cost. Many multilevel inverter configurations have been researched to get a sinusoidal like output voltage wave with minimum circuit components. A multilevel inverter has several advantages over a conventional two level converter that uses high switching frequency pulse width modulation (PWM).The nice features of a multi level inverter can be briefly summarized as follows. Staircase waveform quality: Multilevel inverters not only can generate the output voltages with low distortion, but also can reduce the dv/dt stresses; therefore electromagnetic compatibility (EMC) problems can be reduced. Common mode voltage: Multilevel inverters produce small CM voltage, therefore the stress in the bearings of a motor connected to a multilevel motor drive can be reduced. Furthermore CM voltages can be eliminated by using advanced modulation technique. Input current: Multilevel inverters can draw input current with low distortion. Switching frequency: Multilevel inverters can operate at both fundamental frequency and high switching frequency PWM. It should be noted that lower switching frequency means lower switching loss and higher efficiency. DOI: /IJMTER SHOMX 40

2 There are several multilevel converters are commercialized for high power applications such as Flexible AC transmission systems (FACTS) Controllers, HVDC, Train Traction, Automotive applications, renewable energy power conversion and transmission etc. II. PROPOSED SYSTEM- THIRTY ONE LEVEL INVERTER The proposed single-phase thirty one-level inverter is developed from the existing system. It comprises a Single phase conventional H-bridge inverter, three switches, and three voltage sources. The switching devices used here is MOSFET. Since its operating frequency is higher and produces lower switching losses as compared to the other transistors like BJT and IGBT. Also it is small in size and economical. This H-bridge topology is significantly advantageous over other topologies, i.e., lesser the number of power switches, power diodes, and preferably no capacitors as compared to the inverters of the same number of levels. Proper switching of the inverter can produce thirty one output-voltage levels (Vdc, 14Vdc/15, 13Vdc/15, 12Vdc/15, 11Vdc/15, 10Vdc/15, 9Vdc/15, 8Vdc/15, 7Vdc/15, 6Vdc/15, 5Vdc/15, 4Vdc/15, 3Vdc/15, 2Vdc/15, Vdc/15,0, -Vdc/15,- 2Vdc/15,- 3Vdc/15,- 4Vdc/15,- 5Vdc/15,- 6Vdc/15,- 7Vdc/15,- 8Vdc/15,-)) from the dc supply voltage. Using this technique any number of levels can be achieved with reduced number of switching devices. But here we are implementing a thirty one level inverter topology. Multi carrier topology is used for generating the PWM signals for both the H bridge inverter circuit and the bidirectional switching devices. By using the matlab program will be developed for generating the PWM signals. H-BRIDGE INVERTER: Here the MOSFET based full bridge inverter circuit is cascaded for this thirty one level inverter. Three switches are also connected with this H bridge inverter circuit. The snubber circuit (RC) is connected across all the switches for protecting the switching devices from dv/dt and di/dt ratings. Three diodes are connected parallel to the three switches. It completes the circuit when the corresponding switch is in off position. LOAD: In this project the maximum output power level of the inverter is 10w. The maximum output voltage level of the inverter is 42 volts. For this power rating we can use lamp or small size motors. This project implemented in a prototype. The voltage levels of the three sources are different. So this method of configuration is called as asymmetrical multilevel inverter. The inverter level is decided by both the modulation index and the applied DC voltage level of the inverter. By adjusting the different voltage level we can able to increase the number of levels of the inverter. MCM controller is used for generating the PWM signals the inverter circuit. The switching devices used in this inverter are MOSFET (IRF840). The power handling capacity of the inverter is low because the hardware is developed in a prototype. Figure level Inverter block All rights Reserved 41

3 Figure level Inverter circuit diagram The proposed single-phase thirty one-level inverter was developed from the seven-level inverter. It comprises a Single phase conventional H-bridge inverter, three switches, and three voltage sources. This H-bridge topology is significantly advantageous over other topologies, i.e., less power switch, power diodes, for inverters of the same number of levels. Proper switching of the inverter can produce thirty one output-voltage levels (Vdc, 14Vdc/15, 13Vdc/15, 12Vdc/15, 11Vdc/15, 10Vdc/15, 9Vdc/15, 8Vdc/15, 7Vdc/15, 6Vdc/15, 5Vdc/15, 4Vdc/15, 3Vdc/15, 2Vdc/15, Vdc/15,0, -Vdc/15,- 2Vdc/15,- 3Vdc/15,- 4Vdc/15,- 5Vdc/15,- 6Vdc/15,- 7Vdc/15,- 8Vdc/15,-) 9Vdc/15,- 10Vdc/15,- 11Vdc/15,- 12Vdc/15,- 13Vdc/15,- 14Vdc/15,- Vdc) from the dc supply voltage. Figure level Inverter operation In this project multi carrier pulse width modulation technique is used to generate the thirty one level output voltage. Seven equal amplitude carrier triangular signals with offset is All rights Reserved 42

4 with the sinusoidal reference signal. These PWM signals are given to the switches S1, S2, S3, S4. Then the two sinusoidal signals having 180 degree displacement signals are compared with the carrier triangular signal, these PWM pulses are having dead band, it will avoid the shoot through problem between two devices. These PWM pulses are given to the single phase inverter circuit switches H1, H2, H3, and H4. Here the switching device is MOSFET. III. SIMULATION STUDIES Figure 4. Proposed system Simulink model The figure shows the Simulink model developed in matlab simulation with multi carrier modulation All rights Reserved 43

5 Figure 5. Proposed system MCM comparison The figure shows the PWM generation using multi carrier modulation techniques. The 15 carrier signal and single reference signal is used to generate the PWM pulses. Figure 6. Proposed system PWM pulse to the inverter switches The figure shows the PWM pulses to the inverter switches, the pulses are produced using MCM modulation technique with 10 KHz switching All rights Reserved 44

6 Figure 7. Proposed system PWM pulse to the H bridge inverter The figure shows the PWM pulses to the H bridge inverter switches, it s having 180 degree displacement. It s developed with sinusoidal pulse width modulation technique. Figure 8. Proposed system thirty one level inverter output voltage Figure 9. Proposed system thirty one level inverter output All rights Reserved 45

7 The figure shows the thirty one level inverter voltage and current waveform. The output voltage is nearly sinusoidal waveform. This proposed topology achieved the thirty one level output voltage with only eight switches. Also its THD value also obeys IEEE harmonics standard. The following figure shows the THD value of the thirty one level output voltage waveform. Figure 10. Proposed system thirty one level inverter THD IV. CONCLUSION Multilevel inverters offer improved output waveforms and lower THD. This paper has presented a novel PWM switching scheme for the proposed multilevel inverter. In this project only one reference signal and is compared with a triangular wave signal to generate the PWM signals. Here there are three different DC voltage levels are used in this multi-level inverters. So this method of configuration is known as asymmetrical cascaded inverter. By controlling the modulation index and different levels of DC voltages the thirty one levels of the output voltage s achieved. REFERENCES [1] Peng, M. Calais and V. G. Agelidis, Multilevel converters for single-phase grid connected photovoltaic systems an overview, in Proc. IEEE Int. Symp. Ind. Electron, 1998, vol. 1, pp [2] Single-Phase Seven-Level Grid-Connected Inverter for Photovoltaic System Nasrudin A. Rahim, Senior Member, IEEE, Krismadinata Chaniago, Student Member, IEEE, and Jeyraj Selvaraj [3] 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 [4] P. K. Hinga, T. Ohnishi, and T. Suzuki, A new PWM inverter for pho-tovoltaic power generation system, in Conf. Rec. IEEE Power Electron. Spec. Conf., 1994, pp [5] Y. Cheng, C. Qian, M. L. Crow, S. Pekarek, and S. Atcitty, A comparison of diode-clamped and cascaded multilevel converters for a STATCOM with energy storage, IEEE Trans. Ind. Electron., vol. 53, no. 5, pp , Oct [6] M. Saeedifard, R. Iravani, and J. Pou, A space vector modulation strategy for a back-to-back five-level HVDC converter system, IEEE Trans. Ind. Electron., vol. 56, no. 2, pp , Feb [7] S. Alepuz, S. Busquets-Monge, J. Bordonau, J. A. M. Velasco, C. A. Silva, J.Pontt, and J. Rodríguez, Control strategies based on sym-metrical components for grid-connected converters under voltage dips, IEEE Trans. Ind. Electron., vol. 56, no. 6, pp , Jun [8] J. Rodríguez, J. S. Lai, and F. Z. Peng, Multilevel inverters: A survey of topologies, controls, and applications, IEEE Trans. Ind. Electron., vol. 49, no. 4, pp , Aug [9] J. Rodriguez, S. Bernet, B. Wu, J. O. Pontt, and S. Kouro, Multi-level voltage-source-converter topologies for industrial medium-voltage drives, IEEE Trans. vol. 54, no. 6, pp , Dec [10] M. M. Renge and H. M. Suryawanshi, Five-level diode clamped inverter to eliminate common mode voltage and reduce dv/dt in medium voltage rating induction motor drives, IEEE Trans. Power Electron., vol. 23, no. 4, pp , Jul. All rights Reserved 46