New Three-Phase Symmetrical MultilevelVoltage Source Inverter

ABSTRACT:  

This paper presents a new design and implementation of a three-phase multilevel inverter (MLI) for distributed power generation system using low frequency modulation and sinusoidal pulse width modulation (SPWM) as well. It is a modular type and it can be extended for extra number of output voltage levels by adding additional modular stages. The impact of the proposed topology is its proficiency to maximize the number of voltage levels using a reduced number of isolated dc voltage sources and electronic switches. Moreover, this paper proposes a significant factor (F_C/L), which is developed to define the number of the required components per pole voltage level. A detailed comparison based on (F_C/L) is provided in order to categorize the different topologies of the MLIs addressed in the literature. In addition, a prototype has been developed and tested for various modulation indexes to verify the control technique and performance of the topology. Experimental results show a well-matching and good similarity with the simulation results.

KEYWORDS:

1.      Low frequency modulation

2.      Multi-level inverter

3.      Multi-level inverter comparison factor

4.      Sinusoidal pulse-width modulation (SPWM)

5.      Symmetrical DC power sources

6.      Three-phase

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed three-phase MLI topology.

EXPECTED SIMULATION RESULTS:

Fig. 2. Output line-to-line voltages ( V_AB,V_BC , and V_CA ) with low frequency (50 Hz) modulation technique. (a) Simulation.

Fig. 3. Output phase voltages ( V_AN,V_BN , and V_CN ) with low frequency modulation technique. (a) Simulation.

Fig. 4. Inverter outputs with R-L load (V_AB ,V_AN , and I_AN) with low frequency modulation technique. (a) Simulation.

Fig. 5. Pole voltages for scheme I, m_i =0.95 and f_s=2.5kHz. (a) Simulation.

Fig. 6. Line-to-line voltages for scheme I, m_i =0.95 and f_s=2.5kHz . (a) Simulation.

Fig. 7. Phase voltages for scheme I, m_i =0.95 and f_s=2.5kHz . (a) Simulation.

Fig. 8. Pole voltages for scheme II, m_i =0.95 and f_s=2.5kHz . (a) Simulation.

Fig. 9. Line-to-line voltages for scheme II, m_i =0.95 and f_s=2.5kHz  . (a) Simulation.

Fig. 10. Phase voltages for scheme II, m_i =0.95 and f_s=2.5kHz. (a) Simulation.

Fig. 11. Line-to-line voltage and phase voltage at for scheme I, m_i =0.95 and f_s=2.5kHz . (a) Simulation.

Fig. 12. Line-to-line voltage and phase voltage for scheme II, m_i =0.95 and f_s=2.5kHz . (a) Simulation.

Fig. 13. Inverter output voltages: (a) three phase line-to-line voltages ( V_AB, V_BC, and V_CA ), (b) line-to-line voltage, phase voltage and the phase current under R-L load.

CONCLUSION:

A new modular multilevel inverter topology using two modulation control techniques is presented. The proposed has several advantages compared with existing topologies. A lower number of components count such as isolated dc-power supplies, switching devices, electrolyte capacitors, and power diodes are required. So it exhibits the merits of high efficiency, lower cost, simplified control algorithm, smaller inverter's foot print and increased the overall system reliability. Due to the modularity of the presented topology, it can be extended to higher stages number leads to a good performance issues such as low, low, and low and eliminating the output filter will be obtained. Beside the low frequency modulation, two schemes are successfully applied to control the suggested . This paper also suggests a significant factor, which defines the required components to generate one voltage level across the output pole terminals. The issue related to the cost of each used component is out of scope of this paper. The system simulation model and its control algorithm are developed using PSIM and MATLAB software package tools to validate the proposed topology. A laboratory prototype has been developed and tested for various modulation indexes to verify the control techniques and performance of the topology, the similarity between the simulation and obtained experimental results was confirmed.

REFERENCES:

[1] S. J. Park, F. S. Kang, M. H. Lee, and C. U. Kim, “A new single-phase five-level PWM inverter employing a deadbeat control scheme,” IEEE Trans. Power Electron., vol. 18, no. 3, pp. 831–843, May 2003.

[2] V. G. Agelidis, D. M. Baker, W. B. Lawrance, and C. V. Nayar, “A multilevel PWM inverter topology for photovoltaic applications,” in Proc. Int. Symp. Ind. Electron., Jul. 1997, vol. 2, pp. 589–594.

[3] G. J. Su, “Multilevel DC-link inverter,” IEEE Trans. Ind. Appl., vol. 41, no. 3, pp. 848–854, May–Jun. 2005.

[4] M. Calais, L. J. Borle, and V. G. Agelidis, “Analysis of multicarrier PWM methods for a single-phase five level inverter,” in Proc. Power Electron. Specialists Conf., 2001, vol. 3, pp. 1351–1356.

[5] C. T. Pan, C. M. Lai, and Y. L. Juan, “Output current ripple-free PWM inverters,” IEEE Trans. Circuits Syst. II, Exp. Briefs., vol. 57, no. 10, pp. 823–827, Oct. 2010.

An Efficient Constant Current Controller for PV Solar Power Generator Integrated with the Grid

ABSTRACT:  

This paper presents the detailed design and modeling of grid integrated with the Photovoltaic Solar Power Generator. As the Photovoltaic System uses the solar energy as one of the renewable energies for the electrical energy production has an enormous potential. The PV system is developing very rapidly as compared to its counterparts of the renewable energies. The DC voltage generated by the PV system is boosted by the DC-DC Boost converter. The utility grid is incorporated with the PV Solar Power Generator through the 3-ı PWM DC-AC inverter, whose control is provided by a constant current controller. This controller uses a 3-ı phase locked loop (PLL) for tracking the phase angle of the utility grid and reacts fast enough to the changes in load or grid connection states, as a result, it seems to be efficient in supplying to load the constant voltage without phase jump. The complete mathematical model for the grid connected PV system is developed and simulated. The results verify that the proposed system is proficient to supply the local loads.

KEYWORDS:

1.      PV Solar Power Generator

2.      DC-DC Boost Converter

3.      PWM inverter

4.      PLL

5.      Constant Current Controller (CCC)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 Switching Model of Solar Inverter

EXPECTED SIMULATION RESULTS:

Fig.2 P-V Curve of the Solar Array

Fig. 3 V-I Curve of the Solar Array

Fig. 4 DC voltage delivered by the Boost converter

Fig. 5Inverter output voltage before filtering

Fig. 6 Inverter output voltage after filtering

Fig. 7 Load current for supplying the 2 MW load.

Fig.8 Load current for supplying the load of about 30 MW, 2 MVAr

CONCLUSION:

For improving the energy efficiency and power quality issues with the increment of the world energy demand, the power generation using the renewable energy source is the only solution. There are several countries located in the tropical and temperature regions, where the direct solar density may reach up to 1000W/m2. Hence PV system is considered as a primary resource. In this paper, the detailed modeling of grid connected PV generation system is developed. The DC-DC boost converter is used to optimize the PV array output with the closed loop control for keeping the DC bus voltage to be constant. The 2 level 3-phase inverter is converting the DC into the sinusoidal AC voltage. The control of the solar inverter is provided through the constant current controller. This controller tracks the phase and frequency of the utility grid voltage using the Phase- Locked-Loop (PLL) system and generates the switching pulses for the solar inverter. Using this controller the output voltage of the solar inverter and the grid voltage are in phase. Thus the PV system can be integrated to the grid. The simulation results the presented in this paper to validate the grid connected PV system model and the applied control scheme.

REFERENCES:

[1] A. M. Hava, T. A. Lipo and W. L. Erdman. “Utility interface issues for line connected PWM voltage source converters: a comparative study”, Proceeding of APEC’95, Dallas (USA), pp. 125-132, March 1995.

[2] L. J. BORLE, M. S. DYMOND and C. V. NAYAR, “Development and testing of a 20 kW grid interactive photovoltaic power conditioning system in Western Australia”, IEEE Transaction, Vol. 33, No. 2, pp. 502-508, 1997.

[3] M. Calais, J. Myrzik, T. Spooner, V. Agelidis, “Inverters for single- phase grid connected photovoltaic systems – an overview”, IEEE 33rd Annual Power Electronics Specialists Conference, Volume 4, 23-27 June 2002

[4] S. K. Chung, “Phase-Locked Loop for Grid connected Three-phase Power Conversion Systems”, IEE Proceeding on Electronic Power Application, Vol. 147, No. 3, pp. 213-219, 2000.

[5] S. Rahman, “Going green: the growth of renewable energy”, IEEE Power and Energy Magazine, 16-18 Nov./Dec. 2003.

A 5-level High Efficiency Low Cost Hybrid Neutral Point Clamped Transformerless Inverter for Grid Connected Photovoltaic Application

ABSTRACT:  

With the increase in the level of solar energy integration into the power grid, there arises a need for highly efficient multilevel transformerless grid connected inverter which is able to inject more power into the grid. In this paper, a novel 5-level Hybrid Neutral Point Clamped transformerless  inverter topology is proposed which has no inherent ground leakage current. The proposed inverter is analyzed in detail and its switching pattern to generate multilevel output is discussed. The proposed inverter is compared with some popular transformerless inverter topologies. Simulations and experiments results confirm the feasibility and good performance of the proposed inverter.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1. Proposed hybrid neutral point clamped inverter

EXPECTED SIMULATION RESULTS:

Fig. 2. Inverter operation at UPF

Fig. 3. Inverter operation at 30⁰ lag PF

Fig. 4. Inverter output for increase of modulation index from 0.45 to 0.95

Fig. 5. Inverter output for decrease of modulation index from 0.95 to 0.45

Fig. 6. Dynamic performance of inverter for increase of load

Fig. 7. Dynamic performance of inverter for decrease of load

Fig. 8. Inverter operation with chopper balancing circuit activated

Fig. 9. Inverter operation with chopper balancing circuit deactivated

CONCLUSION:

A 5-level Hybrid neutral point clamped transformerless PV grid connected inverter is presented in this paper. The main characteristics of proposed transformerless inverter are:

1) Lower stress on the grid interfacing inductor, thereby reducing the filtering cost and size as compared to conventional 3-level inverters like H5 and HERIC  inverter.

2) Lower cost as compared to 5L-DCMLI as the proposed inverter requires less no of clamping diodes.

3) Higher power handling capability as compared to conventional 3-level inverters.

4) Higher efficiency as compared to 5L-DCMLI and H5 inverter.

5) No common mode leakage current as the proposed inverter belongs to the family of half bridge inverters.

6) The proposed inverter is capable of exchanging reactive power with the grid.

Therefore, with excellent performance in eliminating the CM current, multilevel output voltage and high efficiency, the proposed inverter provides an exciting alternative to the conventional transformerless grid-connected PV inverters. Moreover, due to its superiority over the 5L-DCMLI in terms of efficiency and cost parameters, the pertinence of the proposed inverter is not limited to grid connected PV inverters and it can find its way for all the applications where currently 5L-DCMLI are employed.

REFERENCES:

[1] M. Calais and V. G. Agelidis,“Multilevel converters for single-phase grid connected photovoltaic systems-an overview,” Industrial Electronics, 1998. Proceedings. ISIE ’98. IEEE International Symposium on, Pretoria, 1998, pp. 224-229 vol.1. doi: 10.1109/ISIE.1998.707781 [2] R. Teodorescu, M. Liserre et al., “Grid converters for photovoltaic and wind power systems”. John Wiley & Sons, 2011, vol. 29.

[3] E. Gubia, P. Sanchis, A. Ursua, J. Lopez, and L. Marroyo, “Ground currents in single phase transformerless photovoltaic systems”, Progress in Photovoltaics: Research and Applications, vol. 15, no. 7, pp. 629650, 2007.

[4] H. Xiao and S. Xie, “Leakage current analytical model and application in single-phase transformerless photovoltaic grid-connected inverter”, IEEE Transactions on Electromagnetic Compatibility, vol. 52, DOI 10.1109/TEMC.2010.2064169, no. 4, pp. 902913, Nov. 2010.

[5] S. Busquets-Monge, J. Rocabert, P. Rodriguez, S. Alepuz and J. Bordonau, “Multilevel Diode-Clamped Converter for Photovoltaic Generators With Independent Voltage Control of Each Solar Array”, in IEEE Transactions on Industrial Electronics, vol. 55, no. 7, pp. 2713-2723, July 2008. Doi: 10.1109/TIE.2008.924011