A Highly Efficient and Reliable Inverter Configuration Based Cascaded Multi-Level Inverter for PV Systems

ABSTRACT:  

This paper presents an improved Cascaded Multi-Level Inverter (CMLI) based on a highly efficient and reliable configuration for the minimization of the leakage current. Apart from a reduced switch count, the proposed scheme has additional features of low switching and conduction losses. The proposed topology with the given PWM technique reduces the high-frequency voltage transitions in the terminal and common-mode voltages. Avoiding high-frequency voltage transitions achieves the minimization of the leakage current and reduction in the size of EMI filters. Furthermore, the extension of the proposed CMLI along with the PWM technique for 2m+1 levels is also presented, where m represents the number of Photo Voltaic (PV) sources.

The proposed PWM technique requires only a single carrier wave for all 2m+1 levels of operation. The Total Harmonic Distortion (THD) of the grid current for the proposed CMLI meets the requirements of IEEE 1547 standard. A comparison of the proposed CMLI with the existing PV Multi-Level Inverter (MLI) topologies is also presented in the paper. Complete details of the analysis of PV terminal and common-mode voltages of the proposed CMLI using switching function concept, simulations, and experimental results are presented in the paper.

KEYWORDS:
  1. Cascaded multi-level inverter
  2. Leakage current
  3. Common-mode voltage
  4. Terminal voltage

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 

Fig. 1. Proposed five-level grid-connected CMLI with PV and parasitic elements.

EXPECTED SIMULATION RESULTS:

 

Fig. 2. Simulation results of proposed five-level CMLI showing the waveforms of : (a) output voltage vuv; (b) grid current iac; (c) terminal voltage vxg; (d) terminal voltage vyg; (e) terminal voltage vzg; (f) leakage current ileak; (g) common-mode voltage vcm.

Fig. 3. Proposed five-level CMLI integrated with MPPT. The subplots give waveforms of : (a) voltage VPV1; (b) voltage VPV2; (c) current IPV1; (d) current IPV2; (e) power PPV1; (f) power PPV2; (g) resultant modulation index ma; (h) output power POUT; (i) modified reference wave vref_modified; (j) inverter output voltage vab.

CONCLUSION:

 In this paper, an improved five-level CMLI with low switch count for the minimization of leakage current in a transformerless PV system is proposed. The proposed CMLI minimizes the leakage current by eliminating the high-frequency transitions in the terminal and common-mode voltages. The proposed topology also has reduced conduction and switching losses which makes it possible to operate the CMLI at high switching frequency.

Furthermore, the solution for generalized 2m+1 levels CMLI is also presented in the paper. The given PWM technique requires only one carrier wave for the generation of 2m+1 levels. The operation, analysis of terminal and common-mode voltages for the CMLI is also presented in the paper. The simulation and experimental results validate the analysis carried out in this paper. The MPPT algorithm is also integrated with the proposed five-level CMLI to extract the maximum power from the PV panels. The proposed CMLI is also compared with the other existing MLI topologies in Table V to show its advantages.

REFERENCES:

[1] Y. Tang, W. Yao, P.C. Loh and F. Blaabjerg, “Highly Reliable Transformerless Photovoltaic Inverters With Leakage Current and Pulsating Power Elimination,” IEEE Trans. Ind. Elect., vol. 63, no. 2, pp. 1016-1026, Feb. 2016.

[2] W. Li, Y. Gu, H. Luo, W. Cui, X. He and C. Xia, “Topology Review and Derivation Methodology of Single-Phase Transformerless Photovoltaic Inverters for Leakage Current Suppression,” IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4537-4551, July 2015.

[3] J. Ji, W. Wu, Y. He, Z. Lin, F. Blaabjerg and H. S. H. Chung, “A Simple Differential Mode EMI Suppressor for the LLCL-Filter-Based Single-Phase Grid-Tied Transformerless Inverter,” IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4141-4147, July 2015.

[4] Y. Bae and R.Y.Kim, “Suppression of Common-Mode Voltage Using a Multicentral Photovoltaic Inverter Topology With Synchronized PWM,” IEEE Trans. Ind. Elect., vol. 61, no. 9, pp. 4722-4733, Sept. 2014.

[5] N. Vazquez, M. Rosas, C. Hernandez, E. Vazquez and F. J. Perez-Pinal, “A New Common-Mode Transformerless Photovoltaic Inverter,” IEEE Trans. Ind. Elect., vol. 62, no. 10, pp. 6381-6391, Oct. 2015.

Three Phase ZVR Topology and Modulation Strategy for Transformerless PV System

ABSTRACT:

Spillage propelled decline is significant for dynamic transformer-less PV systems. In this salute, another three-organize topology and procedure method is proposed. It is gotten from the single-arrange ZVR topology (zero-voltage state rectifier) , all the equivalent the onus framework is without a doubt uncommon. from head to foot side these lines.

ZVR

another style framework two-sided on the Boolean reason field is required to end the interminable ordinary nature voltage, to annul the spillage current. At get along, the disclose tests are done to peruse the feasibility and reasonability of the normal course of action.

  

CIRCUIT DIAGRAM:

Fig. 1. Schematic diagram of three-phase ZVR topology.

 

EXPECTED RESULTS:

  Fig. 2 Experimental results with the dual-carrier modulation. (a) Grid current; (b) Stray capacitor voltage and leakage current

Fig. 3. Experimental results with proposed modulation. (a) Grid current; (b) Stray capacitor voltage and leakage current

Fig. 4 Dynamic experiments with proposed modulation. (a) Phase_A grid voltage and current, (b) dc-link capacitor voltages, stray capacitor voltage and leakage current

Fig. 5. The current and voltage through the ZVR.

 

CONCLUSION:

This how might you do has described the cut and endeavor and clear up assertion of another three-sort out ZVR topology and its change reasoning to renounce the spillage advanced for transformerless PV structures.The disclosures uncover that the spillage current can be in an appealing path decreased with a free hand underneath 300mA by picking the exchanging solicitation of shrewd three-arrange ZVR topology.  This how would you do has recounted the cut and attempt and clarify affirmation of another three-organize ZVR topology and its fluctuate philosophy to deny the spillage progressed for transformerless PV systems. The revelations uncover that the spillage cutting edge can be in an acceptable way diminished with a free hand underneath 300mA by picking the trading request of clever three-organize ZVR topology.

Topology

along the side of that, the about to be tweak is inconsequential to execute. by its own nature, it is flavorsome for three-stage transformerless PV frameworks.

The infinity research is as the extensive on a long shot examination. the capacitor voltage adjusting appliance of the eventual arrangement.

Transformerless Z-Source Four-Leg PV Inverter with Leakage Current Reduction

IEEE Transactions on Power Electronics, 2018 IEEE

ABSTRACT: Due to the lack of electrical isolation, the leakage current is one of the most important issues for transformerless PV systems. In this paper, a new modulation strategy is proposed to reduce the leakage current for Z-Source four-leg transformerless PV inverter. Firstly, the common mode loop model is presented. And then the common mode voltage behavior and the effect of factors on the leakage current are discussed. A new modulation strategy is proposed to achieve the step-up function and constant common mode voltage. Therefore, the leakage current can be suppressed effectively. Finally, the proposed strategy is digitally implemented and tested. The simulation results verify the effectiveness of the proposed solution.

 

KEYWORDS:

  1. Transformerless photovoltaic system
  2. Z source inverter
  3. Modulation
  4. Leakage current.

 

SOFTWARE: MATLAB/SIMULINK

 

CIRCUIT DIAGRAM:

Z-source four-leg inverter for transformerless PV systems

Fig. 1. Z-source four-leg inverter for transformerless PV systems

 

EXPECTED SIMULATION RESULTS:

(a)Common mode voltage VCM

(b) Parasitic capacitance voltage VPV

   

(c) Leakage current ICM

(d) Spectrum analysis of ICM

(e) Grid current

(f) Spectrum analysis of grid current

Fig.2 Simulation results of conventional modulation strategy

(a) Common mode voltage VCM

(b) Parasitic capacitance voltage VPV

(c) Leakage current ICM

(d) Spectrum analysis of ICM

(e) Grid current

(f) Spectrum analysis of grid current

Fig.3 Simulation results of proposed modulation strategy

(a) Conventional modulation strategy.

(b) Proposed modulation strategy

Fig. 4 Simulation results of d from 0.3 to 0.1

Fig.5 Simulation results of duty cycle and leakage current (RMS)

 

CONCLUSION:

This paper has presented the analysis and simulation verification of a new modulation strategy to reduce the leakage current of Z-source four-leg inverter for transformerless PV systems. Our finding indicates that the conventional method fails to eliminate the leakage current. Meanwhile, the leakage current will be higher as the shoot-through duty cycle increases. As for the proposed method, the effect of shoot-through duty cycle variation on the leakage current is small, and the leakage current can be effectively reduced. On the other hand, there is one drawback that the number of switching for the proposed solution is slightly more than that of the traditional one during a carrier cycle. However, compared with the conventional solution, both the leakage current and the THD of grid current can be reduced effectively with the proposed solution. Moreover, the four-leg solution can enable the zero sequence current to circulate, avoiding the dc bias in the load output currents in case of unbalanced loads. Aside from that, the power losses of semiconductor devices can be reduced significantly. Therefore, the proposed solution is attractive for transformerless PV systems.

 

REFERENCES:

  1. Guo, Y. Yang, and T. Zhu, “ESI: A novel three-phase inverter with leakage current attenuation for transformerless PV systems,” IEEE Trans. Ind. Electron., vol. 65, no. 4, pp. 2967-2974, Apr.2018.
  2. Xiao, L. Zhang, and Y. Li, “An improved zero-current-switching single-phase transformerless PV H6 inverter with switching loss-free,” IEEE Trans. Ind. Electron., vol. 64, no. 10, pp. 7896-7905, Oct. 2017.
  3. Zhang, K. Sun, Y. Li, X. Lu, and J. Zhao, “A distributed power control of series connected module-integrated inverters for PV grid-tied applications,” IEEE Trans. Power Electron., vol. 33, no. 9, pp. 7698-7707, Sept. 2018.
  4. Li, Y. Gu, H. Luo, W. Cui, X. He, and C. Xia, “Topology review and derivation methodology of single-phase transformerless photovoltaic inverters for leakage current suppression,” IEEE Trans. Ind. Electron., vol. 62, no. 7, pp. 4537–4551, Jul. 2015.
  5. Yam Siwakoti, and Frede Blaabjerg, “Common-ground-type transformerless inverters for single-phase solar photovoltaic systems,” IEEE Trans. Ind. Electron., vol. 65, no. 3, pp. 2100–2111 Mar. 2018.

H6-type Single Phase Full-Bridge PV Grid-Tied Transformerless Inverters

ABSTRACT:
Photovoltaic (PV) generation systems are broadly employed in transformer less inverters, in order to produce the benefits of high efficiency and low cost. Safety want of leakage currents are met by request the various transformers less inverter topologies. In this paper, three transformer less inverter topologies are decorated such as a family of H6 transformer less inverter topologies with low leakage currents is planned, and the intrinsic relationship between H5 topology, highly efficient and reliable inverter concept (HERIC) topology.

H6 INVERTER

The proposed H6 topology has been discussed as well. For a detailed analysis with operation modes and modulation strategy one of the proposed H6 inverter topologies is captured as an example. Comparison among the HERIC, the H5, and the proposed H6 topologies is been done for the power device costs and power losses.

HERIC

For decide their performances in terms of power efficiency and leakage currents component, a universal prototype is built for these three topologies noticed. Simulation results show that the proposed HERIC topology and the H6 topology achieve similar performance in leakage currents, which is a little bad than that of the H5 topology, but it features higher ability than that of H5 topology.

KEYWORDS:
1. Common-mode voltage
2. Grid-tied inverter
3. Leakage current
4. Photovoltaic (PV) generation system
5. Transformerless inverter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

image002

Fig. 1. Leakage current path for transformerless PV inverters

EXPECTED SIMULATION RESULTS:

image004 image006

Fig. 2. CM voltage and leakage current in H6 topology. (a) CM voltage. (b) Leakage current.

image008 image010

Fig. 3. Drain–source voltages in H6 topology. (a) Voltage stress on S5 and S6 . (b) Detailed waveforms.

image012

Fig. 4. DM characteristic of H6 topology.

image014

Fig. 5. Efficiency comparison of H5, HERIC and H6 topologies.

CONCLUSION:

In this paper, based on the H5 topology, a new current path is formed by inserting a power device between the terminals of PV array and the midpoint of one of bridge legs.

PV ARRAY

As a result, a family of single-phase transformerless full-bridge H6 inverter topologies with low leakage currents is derived. The proposed H6 topologies have the following advantages and evaluated by simulation results:

H6  TOPOLOGY

1) The conversion efficiency of the novel H6 topology is better than that of the H5 topology, and its thermal stress distribution is better than that of the H5 topology;
2) The leakage current is almost the same as HERIC topology, and meets the safety standard;
3) The excellent DM performance is achieved like the isolated full-bridge inverter with uniploar SPWM. Therefore, the proposed H6 topologies are good solutions for the single phase transformerless PV grid-tied inverters.

REFERENCES:
[1] S. B. Kjaer, J. K. Pederson, and F. Blaabjerg, “A review of single-phase grid-connected inverters for photovoltaic modules,” IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1292–1306, Sep/Oct. 2005.
[2] F. Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.
[3] B. Sahan, A. N. Vergara, N. Henze, A. Engler, and P. Zacharias, “A single stage PVmodule integrated converter based on a low-power current source inverter,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2602–2609, Jul.2008.
[4] M. Calais, J. Myrzik, T. Spooner, and V. G. Agelidis, “Inverters for single phase grid connected photovoltaic systems—An overview,” in Proc. IEEE PESC, 2002, vol. 2, pp. 1995–2000.
[5] F. Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.