High-Efficiency Two-Stage Three-LevelGrid-Connected Photovoltaic Inverter

ABSTRACT:

This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. The proposed two-stage inverter comprises a three-level step up converter and a three-level inverter. The three-level step up  converter not only improves the power-conversion efficiency by lowering the voltage stress but also guarantees the balancing of the dc-link capacitor voltages using a simple control algorithm; it also enables the proposed inverter to satisfy the VDE 0126-1-1 standard of leakage current. The three-level inverter minimizes the overall power losses with zero reverse-recovery loss.

Furthermore, it reduces harmonic distortion, the voltage ratings of the semiconductor device, and the electromagnetic interference by using a three-level circuit configuration; it also enables the use of small and low cost filters. To control the grid current effectively, we have used a feed-forward nominal voltage compensator with a mode selector; this compensator improves the control environment by presetting the operating point. The proposed high-efficiency two-stage three-level grid-connected photovoltaic inverter overcomes the low  efficiency problem of conventional two-stage inverters, and it provides high power quality with maximum efficiency of 97.4%. Using a 3-kW prototype of the inverter, we have evaluated the performance of the model and proved its feasibility.

KEYWORDS:

  1. Transformerless
  2. Multilevel
  3. Dc-ac power conversion
  4. Single-phase

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed high-efficiency two-stage three-level grid-connected PV inverter circuit diagram.

EXPECTED SIMULATION RESULTS:

 Fig.2. Simulation results for the leakage current of the proposed twostage

inverter.

Fig.3. Simulation results for the leakage current using a conventional three-level step-up converter of Fig. 2(b) as dc-dc power conversion stage of two-stage inverter.

CONCLUSION: 

A high-efficiency two-stage three-level grid-connected PV inverter and control system are introduced. Also, a theoretical analysis is provided along with the experimental results. By using the novel circuit configuration, the proposed two-stage inverter performs power conversion with low leakage current and high efficiency; in dc-dc power conversion stage, the connection of midpoints of capacitors enables the proposed two-stage inverter to limit the leakage current below 300mA; in dc-ac power conversion stage, the overall power losses are minimized by eliminating the reverse-recovery problems of the MOSFET body diodes. Besides, the proposed inverter with three voltage levels reduces the power losses, harmonic components, voltage ratings, and EMI; it also enables using small and low cost filters.

For the control system, the feedforward nominal voltage compensator also improves the control environment by presetting the operating point. This developed control algorithm makes the proposed inverter feasible. Thus, the proposed high-efficiency two-stage three-level grid connected PV inverter provides high power quality with high power-conversion efficiency. By using a 3-kW prototype, this experiment has verified that the proposed inverter has high efficiency, and the developed control system is suitable for the proposed inverter.

REFERENCES:

[1] B.K. Bose, “Global energy acenario and impact of power electronics in 21st century,” IEEE Transactions on Industrial Electronics, vol. 60, no. 7, pp. 2638-2651, July. 2013.

[2] Y. Zhou, D. C. Gong, B. Huang, and B. A. Peters, “The impacts of carbon tariff on green supply chain design,” IEEE Transactions on Automation Science and Engineering, July. 2015. Available: DOI: 10.1109/TASE.2015.2445316

[3] Y. Wang, X. Lin, and M. Pedram, “A near-optimal model-based control algorithm for households equipped with residential photovoltaic power generation and energy storage systems,” IEEE Transactions on Sustainable Energy, vol. 7, no. 1, pp. 77-86, Jan. 2016.

[4] Y. W. Cho, W. J. Cha, J. M. Kwon, and B. H. Kwon, “Improved  single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems,” IET Renewable Power Generation, vol. 10, no. 2, pp. 166-174, Feb. 2016.

[5] A. Shayestehfard, S. Mekhilef, and H. Mokhlis, “IZDPWMBased feedforward controller for grid-connected inverters under unbalanced and distorted conditions,” IEEE Trans. Ind. Electron., vol. 64, no. 1, pp. 14-21, Jan. 2017.

A Buck & Boost based Grid Connected PV Inverter Maximizing Power Yield from Two PV Arrays in Mismatched Environmental Conditions

ABSTRACT:

A single phase grid connected transformerless photo voltaic (PV) inverter which can operate either in buck or in boost mode, and can extract maximum power simultaneously from two serially connected subarrays while each of the subarray is facing different environmental conditions, is presented in this paper. As the inverter can operate in buck as well as in boost mode depending on the requirement, the constraint on the minimum number of serially connected solar PV modules that is required to form a subarray is greatly reduced. As a result power yield from each of the subarray increases when they are exposed to different environmental conditions. The topological configuration of the inverter and its control strategy are designed so that the high frequency components are not present in the common mode voltage thereby restricting the magnitude of the leakage current associated with the PV arrays within the specified limit. Further, high operating efficiency is achieved throughout its operating range. A detailed analysis of the system leading to the development of its mathematical model is carried out. The viability of the scheme is confirmed by performing detailed simulation studies. A 1.5 kW laboratory prototype is developed, and detailed experimental studies are carried out to corroborate the validity of the scheme.

KEYWORDS:

  1. Grid connection
  2. Single phase
  3. Transformerless
  4. Buck & Boost based PV inverter
  5. Maximum power point
  6. Mismatched environmental condition
  7. Series connected module

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Dual Buck & Boost based Inverter (DBBI)

 EXPECTED SIMULATION RESULTS

 

Fig. 2. Simulated waveform: Variation in (a) ppv1 and ppv2, (b) vpv1 and

vpv2, (c) ipv1 and ipv2 during entire range of operation

Fig.3. Simulated waveform: vg and ig and their magnified views

Fig. 4. Simulated waveform: iL1 and iL2 and their magnified views

Fig. 5. Simulated waveform: vco1 and vco2 and their magnified views

CONCLUSION:

A single phase grid connected transformerless buck and boost based PV inverter which can operate two subarrays at their respective MPP was proposed in this paper. The attractive features of this inverter were i) effect of mismatched environmental conditions on the PV array could be dealt with A single phase grid connected  transformerless buck and boost based PV inverter which can operate two subarrays at their respective MPP was proposed in this paper. The attractive features of this inverter were i) effect of mismatched environmental conditions on the PV array could be dealt with in an effective way, ii) operating efficiency achieved, _euro = 97.02% was high, iii) decoupled control of component converters was possible, iv) simple MPPT algorithm was employed to ensure MPP operation for the component converters, v) leakage current associated with the PV arrays was within the limit mentioned in VDE 0126-1-1. Mathematical analysis of the proposed inverter leading to the development of its small signal model was carried out. The criterion to select the values of the output filter components was presented. The scheme was validated by carrying out detailed simulation studies and subsequently the viability of the scheme was ascertained by carrying out thorough experimental studies on a 1.5 kW prototype of the inverter fabricated for the purpose.

REFERENCES:

[1] T. Shimizu, O. Hashimoto, and G. Kimura, “A novel high-performance utility-interactive photovoltaic inverter system,” IEEE Trans. Power Electron., vol. 18, no. 2, pp. 704-711, Mar. 2003.

[2] S. V. Araujo, P. Zacharias, and R. Mallwitz, “Highly efficient singlephase transformerless inverters for grid-connected photovoltaic systems,” IEEE Trans. Ind. Electron., vol. 57, no. 9, pp. 3118-3128, Sep. 2010.

[3] B. Ji, J. Wang, and J. Zhao, “High-efficiency single-phase transformerless PV H6 inverter with hybrid modulation method,” IEEE Trans. Ind.Electron., vol. 60, no. 5, pp. 2104-2115, May 2013.

[4] R. Gonzalez, E. Gubia, J. Lopez, and L. Marroyo, “Transformerless single phase multilevel-based photovoltaic inverter,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2694-2702, Jul. 2008.

[5] H. Xiao and S. Xie, “Transformerless split-inductor neutral point clamped three-level PV grid-connected inverter,” IEEE Trans. Power Electron., vol. 27, no. 4, pp. 1799-1808, Apr. 2012.

Review and Comparison of Step-Up Transformerless Topologies for Photovoltaic AC-Module Application

ABSTRACT:

This paper presents a inclusive review of step-up single phase non isolated inverters suitable for ac-module use. In order to measure the most feasible solutions of the reviewed topologies, a benchmark is set.

SEMICONDUCTOR

This benchmark is based on a typical ac-module application considering the want for the solar panels and the grid.The selected solutions are produce and simulated complying with the benchmark get passive and semiconductor components ratings in order to perform a comparison in terms of size and cost.

TOPOLOGIES

A discussion of the analyzed topologies concerning the get ratings as well as ground currents is given. Advice for topological solutions submit with the application benchmark are supply.

KEYWORDS:

  1. AC-module
  2. Photovoltaic(PV)
  3. Step-up Inverter
  4. Transformerless

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

image001

Fig.1 Block diagram of a two stage topology for an ac module

STEP-UP TRANSFORMERLESS INVERTERS:

image002

Fig 2 Boost converter and full bridge inverter

Time sharing boost converter with full bridge inverter

Fig 3 Time sharing boost converter with full bridge inverter

Parallel resonant soft switched boost converter and full bridge inverter

Fig 4 Parallel resonant soft switched boost converter and full bridge inverter

Parallel input series-output bipolar dc output converter and full bridge inverter

Fig 5 Parallel input series-output bipolar dc output converter and full bridge inverter

Boost converter and half bridge inverter

Fig 6 Boost converter and half bridge inverter

Boost converter and neutral point clamped inverter

Fig 7 Boost converter and neutral point clamped inverter

Series combined boost and buck boost and half bridge inverter

Fig 8 Series combined boost and buck boost and half bridge inverter

Center-tapped coupled inductor converter with bipolar output and half bridge inverter

Fig  9 Center-tapped coupled inductor converter with bipolar output and half bridge inverter

Single inductor bipolar output buck-boost converter and half bridge inverter

Fig 10 Single inductor bipolar output buck-boost converter and half bridge inverter

 Boost + FB integrated and dual grounded

Fig  11 Boost + FB integrated and dual grounded

Block diagram of a pseudo-dc-link topology for an ac module

Fig 12 Block diagram of a pseudo-dc-link topology for an ac module

Buck-boost DCM converter and unfolding stage

Fig 13 Buck-boost DCM converter and unfolding stage

Noninverting buck-boost DCM converter and unfolding stage

Fig 14 Noninverting buck-boost DCM converter and unfolding stage

Switched inductor buck boost DCM converter and unfolding stage

Fig 15 Switched inductor buck boost DCM converter and unfolding stage

 Boost buck time sharing converter and unfolding stage

Fig 16 Boost buck time sharing converter and unfolding stage

Block diagram of a single stage topology for an ac module

Fig 17 Block diagram of a single stage topology for an ac module

Universal single stage grid connected inverter

Fig 18 Universal single stage grid connected inverter

image019

Fig 19 Integrated boost converter

image020

Fig 20 Differential boost converter

image021

Fig 21 Boost inverter with improved zero crossing.

image022

Fig 22 Integrated Buck boost inverter

image023

Fig 23 Buck Boost inverter with extended input voltage range

image024

Fig 24 Differential buck boost inverter

image025

Fig 25 Two sourced anti parallel buck boost inverter

image026

Fig 26 Single stage full bridge buck boost inverter

image027

Fig 27 Buck boost based single stage inverter

image028

Fig 28 Switched inductor buck boost based single stage inverter

image029

Fig 29 Single inductor buck boost based inverter

image030

Fig 30 Doubly grounded single inductor buck boost based inverter

image031

Fig 31 Single inductor  buck boost based inverter with dual ground

image032

Fig 32 Three switch buck boost inverter

image033

Fig 33 Coupled inductor buck boost inverter

image034

Fig 34 Impedance-admittance conversion theory based inverter

image035

Fig 35 Single phase Z source inverter

image036

Fig 36 Semi quasi Z source inverter with continuous voltage gain

 

CONCLUSION:

In this paper, a inclusive review of single phase non isolated inverters for ac module use is given. Both the grid relation and the solar panel want are analyzed stress the leakage current regulation as it is a main disturb in non isolated PV grid connected inverters.

SEMICONDUCTOR

In order to compare the most suitable solutions of the reviewed topologies under the same requirement, a benchmark of a typical ac module use is set.These solutions have been designed and simulated, get ratings for the passive and the semiconductor components. These ratings are used for the topology comparison in terms of size and cost.

TRANSFORMERLESS

Furthermore, detailed simulations of typical topologies have been achieve using semiconductor and inductor models to estimate the efficiency of the reviewed solutions. As a result of the comparison, the required voltage boost necessary for the connection to the European grid is difficult to achieve with transformerless topologies, but it is able for U.S. want.

DC-DC

Two stage topologies, including the solution with dual grounding efficiency that in theory avoids the ground leakage currents, are the chosen option for the set benchmark in which switching density for the dc-dc stage is set twice than for the dc-ac one.

INVERTER

The two stage combination of a step-up dc-dc converter and a step-up inverter should be thought-out In addition, the consider pseudo-dc-link reach  are an alternative solution in terms of size and cost.

DCM

Moreover, ground currents are normal to be low in these solutions because of the line density interface and weighted ability is the highest due to the flat behavior of the ability with the output power. The consider single stage topologies have higher cost than the other consider solutions and control is normal to be more complex to avoid dc current injection.

RMS

In addition, DCM operation mode allows smaller solutions, including a solution with dual ground efficiency, but ability is lower due to the high RMS currents.