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

Single Phase NPC Inverter Controller with Integrated MPPT for PV Grid Connection

ABSTRACT:  

This paper presents a single-stage three-level Neutral Point Clamped (NPC) inverter for connection to the electrical power grid, with integrated Maximum Power Point Tracking (MPPT) algorithm to extract the maximum power available from solar photovoltaic (PV) panels. This single-stage topology is more compact than the traditional topology, it was chosen because with the proper control strategy. It is suitable to connect the PV panels to the power grid. The paper describes the design of a 5 kW NPC inverter for the interface of PV panels with the power grid, presenting the circuit parameters and the description of the control algorithms. A phase locked loop control is used to connect the inverter into the grid. Then, a proposed DC Link voltage control to regulate the input voltage of the inverter. Although an MPPT algorithm was used to optimize the energy extraction and the system efficiency. Inverter Output Current control to produce an output current (current injected in the power grid) with low Total Harmonic Distortion (THD) implemented in a DSP. Simulation and experimental results verify the correct operation of the proposed system, even with fluctuations in the solar radiation.

KEYWORDS:

1.      Photovoltaic System

2.       Maximum Power Point Tracking (MPPT)

3.      Neutral Point Clamped (NPC) Inverter

4.      Phase-Locked Loop (PLL)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Block diagram of the NPC converter control system.

 EXPECTED SIMULATION RESULTS:

Figure 2. Block diagram of the E-PLL.

Figure 3. Startup of the proposed system with maximum solar radiation: (a)

PV current (ipanels); (b) PV panels voltage (vpanels);

(c) PV panels power (ppanels).

Figure 4. Operation with fluctuations in the solar radiation, from1000 W/m² to

800 W/m² and to 600 W/m: (a) Maximum theoretical power (pmax); (b)

Extracted power PV panels (ppanels); (c) Inverter output current (iout).

Figure 5. Reference current (iref *) and current injected into the power grid (iout).

Figure 6. Power grid voltage (vgrid) and inverter output current (iout).

Figure 7. Voltages in the two capacitors of the DC-link (vc1, vc2).

CONCLUSION:

This paper presents the design, simulation and experimental results of a 5 kW single-stage three-level Neutral Point Clamped (NPC) inverter for connection to the electrical power grid, with integrated Maximum Power Point Tracking (MPPT) algorithm to extract the maximum available power from solar photovoltaic (PV) panels. It also describes the design of the PLL controller, used to track the fundamental power grid voltage in order to synchronize the NPC inverter with the power grid, and to generate a reference for the inverter output current (which consists in the injected power grid current). All the controllers have been implemented using C code, validated by simulation in PSIM, and executed in a DSP. Experimental results indicate that the current injected in the power grid follows the reference, and that the voltages in the two DC-link capacitors are kept balanced. It is shown that the proposed system is able to always extract the maximum power available from the solar PV panels, even when there are solar radiation fluctuations.

REFERENCES:

[1] S. V. Araújo, S. Member, P. Zacharias, and R. Mallwitz, “Highly Efficient Single-Phase Transformerless Inverters for Grid-Connected Photovoltaic Systems,” Ind. Electron. IEEE Trans., vol. 57, no. 9, pp. 3118–3128, 2010.

[2] S. Saridakis, E. Koutroulis, and F. Blaabjerg, “Optimal  Design of Modern Transformerless PV Inverter Topologies,” Energy Conversion, IEEE Trans., vol. 28, no. 2, pp. 394–404, 2013.

[3] R.Teodorescu, M.Liserre, and P.Rodriguez, Grid Converters for Photovoltaic and Wind Power Systems. 2011.

[4] S. Busquets-monge, J. Rocabert, P. Rodríguez, P. Alepuz, and J. Bordonau, “Multilevel Diode-Clamped Converter for Photovoltaic Generators With Independent Voltage Control of Each Solar Array,” Ind. Electron. IEEE Trans., vol. 55, no. 7, pp. 2713–2723, 2008.

[5] P. Panagis, F. Stergiopoulos, P. Marabeas, and S. Manias, “Comparison of State of the Art Multilevel Inverters,” Power Electron. Spec. Conf. 2008. PESC 2008. IEEE, pp. 4296– 4301, 2008.

A Unified Control and Power Management Scheme for PV-Battery-Based Hybrid Microgrids for Both Grid-Connected and Islanded Modes

ABSTRACT:  

Battery storage is usually employed in Photovoltaic (PV) system to mitigate the power fluctuations due to the characteristics of PV panels and solar irradiance. Control schemes for PV-battery systems must be able to stabilize the bus voltages as well as to control the power flows flexibly. This paper proposes a comprehensive control and power management system (CAPMS) for PV-battery-based hybrid microgrids with both AC and DC buses, for both grid-connected and islanded modes. The proposed CAPMS is successful in regulating the DC and AC bus voltages and frequency stably, controlling the voltage and power of each unit flexibly, and balancing the power flows in the systems automatically under different operating circumstances, regardless of disturbances from switching operating modes, fluctuations of irradiance and temperature, and change of loads. Both simulation and experimental case studies are carried out to verify the performance of the proposed method.

KEYWORDS:

1.      Solar PV System

2.      Battery

3.      Control and Power Management System

4.      Distributed Energy Resource

5.      Microgrid

6.      Power Electronics

7.      dSPACE

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. The proposed control and power management system (CAPMS) for PV-battery-based hybrid microgrids.

EXPECTED SIMULATION RESULTS:

Fig.. 2.. (Gb)rid-connected mode Case A-1: (a) power flows and (b) voltage

values of the PV-battery system.

Fig. 3. Grid-connected mode Case A-2: power flows of the PV-battery system.

Fig. 4. Grid-connected mode Case A-3-1: PV array in power-reference mode.

Fig. 5. Grid-connected mode Case A-3-2: DC bus and PV array voltages

during transitions between MPPT and power-reference modes.

Fig. 6. Grid-connected mode Case A-4: the PV-battery system is receiving

power from the grid after 2.2 s.

Fig. 7. Grid-connected mode Case A-5: Reactive power control of the

inverter.

Fig. 8. Grid-connected mode Case A-6: transition from grid-connected to

islanded mode.

Fig. 9. Islanded mode Case B-1: power flows of the PV-battery system with

changing loads.

Fig. 10. Islanded mode Case B-2: battery power changes with PV generation.

Fig. 11. Islanded mode Case B-3: bus voltage control of the PV-battery

system.

 Fig. 12. Islanded mode Case B-4: (a) unsynchronized and (b) synchronized

AC bus voltages (displaying phase-a) when closing the breaker at the PCC.

 CONCLUSION:

This paper proposes a control and power management system (CAPMS) for hybrid PV-battery systems with both DC and AC buses and loads, in both grid-connected and islanded modes. The presented CAPMS is able to manage the power flows in the converters of all units flexibly and effectively, and ultimately to realize the power balance between the hybrid microgrid system and the grid. Furthermore, CAPMS ensures a reliable power supply to the system when PV power fluctuates due to unstable irradiance or when the PV array is shut down due to faults. DC and AC buses are under full control by the CAPMS in both grid-connected and islanded modes, providing a stable voltage environment for electrical loads even during transitions between these two modes. This also allows additional loads to access the system without extra converters, reducing operation and control costs. Numerous simulation and experimental case studies are carried out in Section IV that verifies the satisfactory performance of the proposed CAPMS.

REFERENCES:

[1] T. A. Nguyen, X. Qiu, J. D. G. II, M. L. Crow, and A. C. Elmore, “Performance characterization for photovoltaic-vanadium redox battery microgrid systems,” IEEE Trans. Sustain. Energy, vol. 5, no. 4, pp. 1379–1388, Oct 2014.

[2] S. Kolesnik and A. Kuperman, “On the equivalence of major variable step- size MPPT algorithms,” IEEE J. Photovolt., vol. 6, no. 2, pp. 590– 594, March 2016.

[3] H. A. Sher, A. F. Murtaza, A. Noman, K. E. Addoweesh, K. Al-Haddad, and M. Chiaberge, “A new sensorless hybrid MPPT algorithm based on fractional short-circuit current measurement and P&O MPPT,” IEEE Trans. Sustain. Energy, vol. 6, no. 4, pp. 1426–1434, Oct 2015.

[4] Y. Riffonneau, S. Bacha, F. Barruel, and S. Ploix, “Optimal power flow management for grid connected PV systems wi0th batteries,” IEEE Trans. Sustain. Energy, vol. 2, no. 3, pp. 309–320, July 2011.

[5] H. Kim, B. Parkhideh, T. D. Bongers, and H. Gao, “Reconfigurable solar converter: A single-stage power conversion PV-battery system,” IEEE Trans. Power Electron., vol. 28, no. 8, pp. 3788–3797, Aug 2013.