Special Issue "Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Solar Energy and Photovoltaic Systems".

Deadline for manuscript submissions: 30 September 2020.

Special Issue Editors

Prof. Dr. Dmitri Vinnikov
Website
Guest Editor
Department of Electrical Power Engineering and Mechatronics, School of Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia
Interests: power electronics; renewable energy; photovoltaics; electrical engineering; impedance-source converters
Prof. Dr. Samir Kouro
Website
Guest Editor
Electronics Engineering Department, Universidad Técnica Federico Santa María, Valparaiso 2390123, Chile
Interests: power electronics; renewable energy; multilevel converters; wind energy conversion systems; electromobility
Prof. Dr. Yongheng Yang
Website
Guest Editor

Special Issue Information

Dear colleague,

The cost and efficiency of PV systems improved significantly, which made them commercially attractive. Nevertheless, feasibility of small-scale installations is limited by the existing technologies that have not yet properly addressed issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty (reliability) improvement to match PV module lifespan; voltage operation range extension for application flexibility; and embedded energy storage for load shifting, have put small-scale PV systems again on the hot spot. This special issue aims to concentrate the latest developments and allow researchers to discuss and share experiences to advance this technology.

Topics of the Special Issue include but are not limited to:

  • Transformerless PV string inverters with a wide MPPT range
  • PV string inverter topologies without electrolytic capacitors
  • Partial power processing dc-dc converters for distributed PV architectures
  • High step-up voltage ratio dc-dc converters
  • PV power optimizers and their control
  • PV microinverters with an improved MPPT range
  • Topologies for increased reliability and warranty extension
  • Sub-module PV power converter topologies
  • Global MPPT algorithms for PV systems under partial shading conditions
  • Advanced control techniques for PV inverters to provide ancillary services to the grid
  • Active power control strategies: absolute active power control, delta power control, ramp-rate control, etc.
  • Active power decoupling in single-phase PV inverters
  • Module-level PV system monitoring and diagnosis
  • Efficiency and reliability of PV systems

Prof. Dr. Dmitri Vinnikov
Prof. Dr. Samir Kouro
Prof. Dr. Yongheng Yang
Guest Editors

Manuscript Submission Information

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Keywords

  • PV systems
  • power control
  • PV inverters
  • dc-dc converters
  • converter topologies
  • efficiency and reliability

Published Papers (20 papers)

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Research

Open AccessArticle
Step-Up Series Resonant DC–DC Converter with Bidirectional-Switch-Based Boost Rectifier for Wide Input Voltage Range Photovoltaic Applications
Energies 2020, 13(14), 3747; https://doi.org/10.3390/en13143747 - 21 Jul 2020
Abstract
This paper proposes a high gain DC–DC converter based on the series resonant converter (SRC) for photovoltaic (PV) applications. This study considers low power applications, where the resonant inductance is usually relatively small to reduce the cost of the converter realization, which results [...] Read more.
This paper proposes a high gain DC–DC converter based on the series resonant converter (SRC) for photovoltaic (PV) applications. This study considers low power applications, where the resonant inductance is usually relatively small to reduce the cost of the converter realization, which results in low-quality factor values. On the other hand, these SRCs can be controlled at a fixed switching frequency. The proposed topology utilizes a bidirectional switch (AC switch) to regulate the input voltage in a wide range. This study shows that the existing topology with a bidirectional switch has a limited input voltage regulation range. To avoid this issue, the resonant tank is rearranged in the proposed converter to the resonance capacitor before the bidirectional switch. By this rearrangement, the dependence of the DC voltage gain on the duty cycle is changed, so the proposed converter requires a smaller duty cycle than that of the existing counterpart at the same gain. Theoretical analysis shows that the input voltage regulation range is extended to the region of high DC voltage gain values at the maximum input current. Contrary to the existing counterpart, the proposed converter can be realized with a wide range of the resonant inductance values without compromising the input voltage regulation range. Nevertheless, the proposed converter maintains advantages of the SRC, such as zero voltage switching (ZVS) turn-on of the primary-side semiconductor switches. In addition, the output-side diodes are turned off at zero current. The proposed converter is analyzed and compared with the existing counterpart theoretically and experimentally. A 300 W experimental prototype is used to validate the theoretical analysis of the proposed converter. The peak efficiency of the converter is 96.5%. Full article
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Open AccessArticle
Energy Storage for 1500 V Photovoltaic Systems: A Comparative Reliability Analysis of DC- and AC-Coupling
Energies 2020, 13(13), 3355; https://doi.org/10.3390/en13133355 - 01 Jul 2020
Cited by 1
Abstract
There is an increasing demand in integrating energy storage with photovoltaic (PV) systems to provide more smoothed power and enhance the grid-friendliness of solar PV systems. To integrate battery energy storage systems (BESS) to an utility-scale 1500 V PV system, one of the [...] Read more.
There is an increasing demand in integrating energy storage with photovoltaic (PV) systems to provide more smoothed power and enhance the grid-friendliness of solar PV systems. To integrate battery energy storage systems (BESS) to an utility-scale 1500 V PV system, one of the key design considerations is the basic architecture selection between DC- and AC-coupling. Hence, it is necessary to assess the reliability of the power conversion units, which are not only the key system components, but also represent the most reliability-critical parts, in order to ensure an efficient and reliable 1500 V PV-battery system. Thus, this paper investigates the BESS solutions of DC- and AC-coupled configurations for 1500 V PV systems with a comparative reliability analysis. The reliability analysis is carried out through a case study on a 160 kW/1500 V PV-system integrated DC- or AC-coupled BESS for PV power smoothing and ramp-rate regulation. In the analysis, all of the DC-DC and DC-AC power interfacing converters are taken into consideration along with component-, converter-, and system-level reliability evaluation. The results reveal that the reliability of the 1500 V PV inverter can be enhanced with the DC-coupled BESS, while seen from the system-level reliability (i.e., a PV-battery system), both of the DC- and AC-coupled BESSs will affect the overall system reliability, especially for the DC-coupled case. The findings can be added into the design phase of 1500 V PV systems in a way to further lower the cost of energy. Full article
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Open AccessArticle
Modular Multilevel Converter for Photovoltaic Application with High Energy Yield under Uneven Irradiance
Energies 2020, 13(10), 2619; https://doi.org/10.3390/en13102619 - 21 May 2020
Abstract
The direct integration of Photovoltaic (PV) to the three-phase Modular Multilevel Converter (MMC) without dc–dc converters results in high-efficiency PV power plant with increased energy yield. The arm power control method for the MMC further improves the extraction of available power under uneven [...] Read more.
The direct integration of Photovoltaic (PV) to the three-phase Modular Multilevel Converter (MMC) without dc–dc converters results in high-efficiency PV power plant with increased energy yield. The arm power control method for the MMC further improves the extraction of available power under uneven irradiance across different phases of the MMC. However, the uneven irradiance between the sub-modules results in residual voltage that results in harmonics and unbalance components. In this paper, the effect of uneven irradiance across the sub-module of the MMC is investigated with arm power control method. A modified balancing algorithm for the arm power control of the MMC is proposed which enables balanced power to be injected into ac grid despite uneven irradiance across the sub-modules in the MMC. The modified balancing algorithm enables to keep the unbalance in the phase currents below 10% and the Total Harmonic Distortion (THD) is confined as per IEEE 519 standard. Full article
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Open AccessArticle
A Family of Single-Stage, Buck-Boost Inverters for Photovoltaic Applications
Energies 2020, 13(7), 1675; https://doi.org/10.3390/en13071675 - 03 Apr 2020
Cited by 1
Abstract
This paper introduces a family of single-stage buck-boost DC/AC inverters for photovoltaic (PV) applications. The high-gain feature was attained by applying a multi-winding tapped inductor, and thus, the proposed topologies can generate a grid-level AC output voltage without using additional high step-up stages. [...] Read more.
This paper introduces a family of single-stage buck-boost DC/AC inverters for photovoltaic (PV) applications. The high-gain feature was attained by applying a multi-winding tapped inductor, and thus, the proposed topologies can generate a grid-level AC output voltage without using additional high step-up stages. The proposed topologies had a low component count and consisted of a single magnetic device and three or four power switches. Moreover, the switches were assembled in a push-pull or half/full-bridge arrangement, which allowed using commercial low-cost driver-integrated circuits. In this paper, the operation principle and comparison of the proposed topologies are presented. The feasibility of the proposed topologies was verified by simulations and experimental tests. Full article
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Open AccessArticle
A Topology Synthetization Method for Single-Phase, Full-Bridge, Transformerless Inverter with Leakage Current Suppression—Part II
Energies 2020, 13(2), 446; https://doi.org/10.3390/en13020446 - 16 Jan 2020
Cited by 1
Abstract
This paper proposes a topology derivation methodology to achieve small leakage current or zero leakage current for photovoltaic application. The core of the proposed method is a unified topology model and MN principle to show how to derive all possible topologies based on [...] Read more.
This paper proposes a topology derivation methodology to achieve small leakage current or zero leakage current for photovoltaic application. The core of the proposed method is a unified topology model and MN principle to show how to derive all possible topologies based on unipolar sinusoidal pulse width modulation (USPWM) and double-frequency USPWM (DFUSPWM). Part II of this paper discusses the topology synthetization method to achieve zero leakage current. Two types of neutral point clamped (NPC) topologies based on USPWM and DFUSPWM are elaborated. Two possible connections for the NPC cell are introduced, and detailed NPC topology derivation procedures are also provided. All existing NPC topologies are derived, and twenty-two new NPC topologies are found based on the new topology derivation methodology for a single-phase, full-bridge, transformerless inverter. Full article
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Open AccessArticle
A Topology Synthetization Method for Single-Phase, Full-Bridge, Transformerless Inverter with Leakage Current Suppression Part I
Energies 2020, 13(2), 434; https://doi.org/10.3390/en13020434 - 16 Jan 2020
Cited by 1
Abstract
Single-phase full-bridge transformerless topologies, such as the H5, H6, or the highly efficient and reliable inverter concept (HERIC) topologies, are commonly used for leakage current suppression for photovoltaic (PV) applications. The main derivation methodology of full-bridge topologies has been used based on both [...] Read more.
Single-phase full-bridge transformerless topologies, such as the H5, H6, or the highly efficient and reliable inverter concept (HERIC) topologies, are commonly used for leakage current suppression for photovoltaic (PV) applications. The main derivation methodology of full-bridge topologies has been used based on both a DC-based decoupling model and an AC-based decoupling model. However, this methodology is not suited to the search for all possible topologies, and cannot verify whether they are inclusive. Part I of this paper will propose a new topology derivation methodology based on unipolar sinusoidal pulse width modulation (USPWM) to search all possible full-bridge topologies for leakage current suppression. First of all, a unified circuit model is proposed, instead of the DC- and AC-based models. Secondly, a mathematic method called the MN principle is then proposed to search for all possible topologies, and a derivation procedure is provided. It was verified that all existing topologies could be found using the proposed method; furthermore, seven new topologies were derived. The proposed topology derivation methodology is extended to search topologies under Double-Frequency USPWM (DFUSPWM). Twenty topologies under USPWM and four topologies under DFUSPWM have been derived. Full article
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Open AccessArticle
Active and Reactive Power Control of a PV Generator for Grid Code Compliance
Energies 2019, 12(20), 3872; https://doi.org/10.3390/en12203872 - 12 Oct 2019
Cited by 3
Abstract
As new grid codes have been created to permit the integration of large scale photovoltaic power plants into the transmission system, the enhancement of the local control of the photovoltaic (PV) generators is necessary. Thus, the objective of this paper is to present [...] Read more.
As new grid codes have been created to permit the integration of large scale photovoltaic power plants into the transmission system, the enhancement of the local control of the photovoltaic (PV) generators is necessary. Thus, the objective of this paper is to present a local controller of active and reactive power to comply the new requirements asked by the transmission system operators despite the variation of ambient conditions without using extra devices. For this purpose, the control considers the instantaneous capability curves of the PV generator which vary due to the change of solar irradiance, temperature, dc voltage and modulation index. To validate the control, the PV generator is modeled in DIgSILENT PowerFactory ® and tested under different ambient conditions. The results show that the control developed can modify the active and reactive power delivered to the desired value at different solar irradiance and temperature. Full article
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Open AccessArticle
Photovoltaic Energy Yield Improvement in Two-Stage Solar Microinverters
Energies 2019, 12(19), 3774; https://doi.org/10.3390/en12193774 - 03 Oct 2019
Cited by 1
Abstract
The focus in this paper is on the two-stage photovoltaic (PV) microinverters using a buck-boost dc/dc front-end converter. Wide input voltage range of the front-end converter enables operation under shaded conditions but results in mediocre performance in the typical voltage range. These microinverters [...] Read more.
The focus in this paper is on the two-stage photovoltaic (PV) microinverters using a buck-boost dc/dc front-end converter. Wide input voltage range of the front-end converter enables operation under shaded conditions but results in mediocre performance in the typical voltage range. These microinverters can be controlled with either fixed or variable dc-link voltage control methods. The latter improves the converter efficiency considerably in the range of the most probable maximum power point (MPP) locations. However, the buck-boost operation of the front-end converter results in noticeable variations of the efficiency across the input voltage range. As a result, conventional weighted efficiency metrics cannot be used to predict annual energy productions by the microinverters. This paper proposes a new methodology for the estimation of annual energy production based on annual profiles of the solar irradiance and ambient temperature. Using this methodology, quantification of the annual energy production is provided for two geographical locations. Full article
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Open AccessArticle
Hierarchical Control with Fast Primary Control for Multiple Single-Phase Electric Springs
Energies 2019, 12(18), 3511; https://doi.org/10.3390/en12183511 - 12 Sep 2019
Abstract
An electric spring (ES) is a new power compensation device which becomes useful for the large-scale integration of renewable energy sources into the grid. However, when the grid contains two or more ESs connected at different nodes, a voltage drop occurs between the [...] Read more.
An electric spring (ES) is a new power compensation device which becomes useful for the large-scale integration of renewable energy sources into the grid. However, when the grid contains two or more ESs connected at different nodes, a voltage drop occurs between the nodes due to the line impedance. Therefore, the voltage of the ES-stabilized nodes cannot be set at the same reference (e.g., 220 V), otherwise one or more ESs break away because of the voltage windup. In this paper, a hierarchical control of multiple ESs tied to a microgrid is proposed to account for the line voltage drop. The primary control relies on the power decoupling control; it is designed for islanded operation of the microgrid, which improves the dynamics of both the voltage and frequency regulation. The secondary control relies on the droop control; it is introduced to coordinate the operation of the ESs by modifying the reference voltage of each ES dynamically. Advantages and disadvantages of the proposed hierarchical control are analyzed together with the explanations of the algorithms developed for its realization. At last, effectiveness of the arranged control system is validated by simulations on the MATLAB/Simulink platform. Full article
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Open AccessArticle
Regulation Performance of Multiple DC Electric Springs Controlled by Distributed Cooperative System
Energies 2019, 12(18), 3422; https://doi.org/10.3390/en12183422 - 05 Sep 2019
Abstract
DC electric springs (DCESs) have been recently developed to improve the voltage stability of a DC microgrid. A lately proposed DCES topology is comprised of a DC/DC three port converter (TPC), a bi-directional buck-boost converter (BBC) and a battery, and is arranged as [...] Read more.
DC electric springs (DCESs) have been recently developed to improve the voltage stability of a DC microgrid. A lately proposed DCES topology is comprised of a DC/DC three port converter (TPC), a bi-directional buck-boost converter (BBC) and a battery, and is arranged as follows: The TPC input port is fed by a renewable energy source (RES) whilst the two TPC output ports supply a non-critical load (NCL) and a critical load (CL) separately; in turn, BBC together with the battery constitutes the DCES energy storage unit (ESU) and is connected in parallel to CL. In this paper, a set of DCESs with such a topology and with their CLs connected to a common DC bus is considered. The control of the DCESs is built up around a distributed cooperative system having two control levels, namely primary and secondary, each of them endowed with algorithms committed to specific tasks. The structure of the control levels is explicated and their parameters are designed. The control system is applied to a DCES set taken as a study-case and tested by simulation. The results of the tests show the excellent performance of the control system in both regulating the CL DC bus voltage and keeping the state-of-charge of the battery within predefined limits. Full article
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Open AccessArticle
Ripple Vector Cancellation Modulation Strategy for Single-Phase Quasi-Z-Source Inverter
Energies 2019, 12(17), 3344; https://doi.org/10.3390/en12173344 - 30 Aug 2019
Cited by 1
Abstract
The double-frequency (2ω) power flows through the DC side of the single-phase quasi-Z-source inverter (QZSI) leads to the 2ω voltage ripple of capacitors and 2ω current ripple of inductors. This paper proposes a ripple vector cancellation modulation strategy (RVCMS) based on the thought [...] Read more.
The double-frequency (2ω) power flows through the DC side of the single-phase quasi-Z-source inverter (QZSI) leads to the 2ω voltage ripple of capacitors and 2ω current ripple of inductors. This paper proposes a ripple vector cancellation modulation strategy (RVCMS) based on the thought of ripple vector cancellation. By analyzing the mechanism of ripple generation and transmission, we can obtain a variation of a shoot-through duty cycle to generate a compensated 2ω ripple used to cancel the 2ω current ripple of inductors caused by the 2ω ripple of DC link current, and the 2ω compensated variation of a shoot-through duty cycle with a specific amplitude and phase is added to the constant shoot-through duty cycle. Finally, simulation and experimental results demonstrate the correctness and effectiveness of the proposed modulation strategy for the single-phase QZSI. Full article
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Open AccessArticle
Evaluation of Interconnection Configuration Schemes for PV Modules with Switched-Inductor Converters under Partial Shading Conditions
Energies 2019, 12(14), 2802; https://doi.org/10.3390/en12142802 - 21 Jul 2019
Cited by 3
Abstract
Partial shading on photovoltaic (PV) arrays reduces the overall output power and causes multiple maximas on the output power characteristics. Due to the introduction of multiple maximas, mismatch power losses become apparent among multiple PV modules. These mismatch power losses are not only [...] Read more.
Partial shading on photovoltaic (PV) arrays reduces the overall output power and causes multiple maximas on the output power characteristics. Due to the introduction of multiple maximas, mismatch power losses become apparent among multiple PV modules. These mismatch power losses are not only a function of shading characteristics, but also depend on the placement and interconnection patterns of the shaded modules within the array. This research work is aimed to assess the performance of 4 × 4 PV array under different shading conditions. The desired objective is to attain the maximum output power from PV modules at different possible shading patterns by using power electronic-based differential power processing (DPP) techniques. Various PV array interconnection configurations, including the series-parallel (SP), total-cross-tied (TCT), bridge-linked (BL), and center-cross-tied (CCT) are considered under the designed shading patterns. A comparative performance analysis is carried out by analyzing the output power from the DPP-based architecture and the traditional Schottky diode-based architecture. Simulation results show the gain in the output power by using the DPP-based architecture in comparison to the traditional bypassing diode method. Full article
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Open AccessEditor’s ChoiceArticle
Experimental Comparison of Two-Level Full-SiC and Three-Level Si–SiC Quasi-Z-Source Inverters for PV Applications
Energies 2019, 12(13), 2509; https://doi.org/10.3390/en12132509 - 28 Jun 2019
Cited by 4
Abstract
The paper presents a comparative study of two solar string inverters based on the Quasi-Z-Source (QZS) network. The first solution comprises a full-SiC two-level QZS inverter, while the second design was built based on a three-level neutral-point-clamped QZS inverter with Silicon based Metal–Oxide–Semiconductor [...] Read more.
The paper presents a comparative study of two solar string inverters based on the Quasi-Z-Source (QZS) network. The first solution comprises a full-SiC two-level QZS inverter, while the second design was built based on a three-level neutral-point-clamped QZS inverter with Silicon based Metal–Oxide–Semiconductor Field-Effect Transistors (Si MOSFETs). Several criteria were taken into consideration: the size of passive elements, thermal design and size of heatsinks, voltage stress across semiconductors, and efficiency investigation. The Photovoltaic (PV)-string rated at 1.8 kW power was selected as a case study system. The advantages and drawbacks of both solutions are presented along with conclusions. Full article
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Open AccessFeature PaperArticle
Research on the Filters for Dual-Inverter Fed Open-End Winding Transformer Topology in Photovoltaic Grid-Tied Applications
Energies 2019, 12(12), 2338; https://doi.org/10.3390/en12122338 - 18 Jun 2019
Abstract
Owing to the necessity of the transformer for the multi-parallel inverters connected to the medium-voltage (MV) grid, the conventional multi-parallel inverter topology can be reconfigured to the dual-inverter fed open-end winding transformer (DI-OEWT) topology to obtain lower output voltage harmonics, which can reduce [...] Read more.
Owing to the necessity of the transformer for the multi-parallel inverters connected to the medium-voltage (MV) grid, the conventional multi-parallel inverter topology can be reconfigured to the dual-inverter fed open-end winding transformer (DI-OEWT) topology to obtain lower output voltage harmonics, which can reduce the requirement of the filter inductance. However, due to the special structure of the DI-OEWT topology, the arrangement scheme of the filter can be more than one kind, and different schemes may affect the filter performance. In this paper, research on the existing two kinds of filters, as well as a proposed one, for the DI-OEWT topology used in photovoltaic grid-tied applications is presented. The equivalent circuits of these filters are derived, and based on this, the harmonic suppression capability of these filters is analyzed and compared. Furthermore, a brief parameter design method of these filters is also introduced, and based on the design examples, the inductance and capacitance requirements of these filters are compared. In addition, these filters are also evaluated in terms of the applicability for fault tolerance. At last, the analysis is verified through an experiment on a 30 kW dual-three-level inverter prototype. Full article
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Open AccessArticle
A Novel Photovoltaic Virtual Synchronous Generator Control Technology Without Energy Storage Systems
Energies 2019, 12(12), 2240; https://doi.org/10.3390/en12122240 - 12 Jun 2019
Abstract
Photovoltaic virtual synchronous generator (PV-VSG) technology, by way of simulating the external characteristics of a synchronous generator (SG), gives the PV energy integrated into the power grid through the power electronic equipment the characteristics of inertial response and active frequency response (FR)—this attracts [...] Read more.
Photovoltaic virtual synchronous generator (PV-VSG) technology, by way of simulating the external characteristics of a synchronous generator (SG), gives the PV energy integrated into the power grid through the power electronic equipment the characteristics of inertial response and active frequency response (FR)—this attracts much attention. Due to the high volatility and low adjustability of PV energy output, it does not have the characteristics of a prime mover (PM), so it must be equipped with energy storage systems (ESSs) in the DC or AC side to realize the PV-VSG technology. However, excessive reliance on ESSs will inevitably affect the application of VSG technology in practical PV power plants (PV-PPs). In view of this, this paper proposes the PV power reserve control type VSG (PV-PRC-VSG) control strategy. By reducing the active power output of part of the PV-PPs, the internal PV-PPs can maintain a part of the active power up/down-regulation ability in real time, instead of relying on external ESSs. By adjusting the active reserve power of this part, the output of the PV-PPs can be controlled within a certain range, and the PV-PPs can better simulate the PM characteristics and realize the FR of the grid by combining the VSG technology. At the same time, the factors affecting the reserve ratio are analyzed, and the position of the voltage operating point in PRC mode is deduced. Finally, the simulation results show that the proposed control strategy is effective and correct. Full article
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Open AccessArticle
A Research on Cascaded H-Bridge Module Level Photovoltaic Inverter Based on a Switching Modulation Strategy
Energies 2019, 12(10), 1851; https://doi.org/10.3390/en12101851 - 15 May 2019
Cited by 6
Abstract
The stable operating region of a photovoltaic (PV) cascaded H-bridge (CHB) grid-tied module level inverter is extended by adopting the hybrid modulation strategy. However, the traditional single hybrid modulation method is unable to regulate the DC-side voltage of each module precisely, which may [...] Read more.
The stable operating region of a photovoltaic (PV) cascaded H-bridge (CHB) grid-tied module level inverter is extended by adopting the hybrid modulation strategy. However, the traditional single hybrid modulation method is unable to regulate the DC-side voltage of each module precisely, which may aggravate the fluctuation of modules’ DC-side voltages or even cause the deviation of modules’ DC-side voltages under some fault conditions and, thus, degrade the energy harvesting of PV panels. To tackle this problem, a switching modulation strategy for PV CHB inverter is proposed in this paper. When the CHB inverter is operating in normal mode, the hybrid modulation strategy containing the zero state is adopted to suppress DC-side voltage fluctuation, thereby, improving the output power of PV modules. When the CHB inverter is operating in fault mode owing to failing solar panels, the hybrid modulation strategy without the zero state is utilized to make the DC-side voltages reach the references and, thus, maintain a higher energy yield under fault conditions. Experimental results achieved by a laboratory prototype of a single-phase eleven-level CHB inverter demonstrate both the feasibility and effectiveness of the proposed method. Full article
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Open AccessArticle
Energy Storage Sizing Strategy for Grid-Tied PV Plants under Power Clipping Limitations
Energies 2019, 12(9), 1812; https://doi.org/10.3390/en12091812 - 13 May 2019
Cited by 3
Abstract
This paper presents an analyses of an Energy Storage System (ESS) for grid-tied photovoltaic (PV) systems, in order to harness the energy usually lost due to PV array oversizing. A real case of annual PV power generation analysis is presented to illustrate the [...] Read more.
This paper presents an analyses of an Energy Storage System (ESS) for grid-tied photovoltaic (PV) systems, in order to harness the energy usually lost due to PV array oversizing. A real case of annual PV power generation analysis is presented to illustrate the existing problem and future solutions. Three PV modeling techniques have been applied to estimate non-measured non-harnessed PV power to provide an ESS energy and power sizing strategy. Moreover, a control strategy to store or release power from the DC-link, without modifying the Maximum Power Point Tracking (MPPT) strategy, is presented. The results show an estimation of the annual power loss caused by oversizing the PV array. The ESS sizing strategy gives insight into not only the energy requirements, but also the power requirements of the system. Simulation results show that the proposed ESS control strategy is capable of harnessing the extra power without modifying the existing power converter of the PV plant nor its control strategy. Full article
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Open AccessArticle
Five-Level T-type Cascade Converter for Rooftop Grid-Connected Photovoltaic Systems
Energies 2019, 12(9), 1743; https://doi.org/10.3390/en12091743 - 08 May 2019
Cited by 4
Abstract
Multilevel converters are widely considered to be the most suitable configurations for renewable energy sources. Their high-power quality, efficiency and performance make them interesting for PV applications. In low-power applications such as rooftop grid-connected PV systems, power converters with high efficiency and reliability [...] Read more.
Multilevel converters are widely considered to be the most suitable configurations for renewable energy sources. Their high-power quality, efficiency and performance make them interesting for PV applications. In low-power applications such as rooftop grid-connected PV systems, power converters with high efficiency and reliability are required. For this reason, multilevel converters based on parallel and cascaded configurations have been proposed and commercialized in the industry. Motivated by the features of multilevel converters based on cascaded configurations, this work presents the modulation and control of a rooftop single-phase grid-connected photovoltaic multilevel system. The configuration has a symmetrical cascade connection of two three-level T-type neutral point clamped power legs, which creates a five-level converter with two independent string connections. The proposed topology merges the benefits of multi-string PV and symmetrical cascade multilevel inverters. The switching operation principle, modulation technique and control scheme under an unbalanced power operation among the cell are addressed. Simulation and experimental validation results in a reduced-scale power single-phase converter prototype under variable conditions at different set points for both PV strings are presented. Finally, a comparative numerical analysis between other T-type configurations to highlight the advantages of the studied configuration is included. Full article
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Open AccessArticle
Compact Single-Stage Micro-Inverter with Advanced Control Schemes for Photovoltaic Systems
Energies 2019, 12(7), 1234; https://doi.org/10.3390/en12071234 - 31 Mar 2019
Cited by 2
Abstract
This paper proposes a grid-connected single-stage micro-inverter with low cost, small size, and high efficiency to drive a 320 W class photovoltaic panel. This micro-inverter has a new and advanced topology that consists of an interleaved boost converter, a full-bridge converter, and a [...] Read more.
This paper proposes a grid-connected single-stage micro-inverter with low cost, small size, and high efficiency to drive a 320 W class photovoltaic panel. This micro-inverter has a new and advanced topology that consists of an interleaved boost converter, a full-bridge converter, and a voltage doubler. Variable switching frequency and advanced burst control schemes were devised and implemented. A 320 W prototype micro-inverter was very compact and slim with 60-mm width, 310-mm length, and 30-mm height. In evaluations, the proposed micro-inverter achieved CEC weighted efficiency of 95.55%, MPPT efficiency >95% over the entire load range, and THD 2.65% at the rated power. The proposed micro-inverter is well suited for photovoltaic micro-inverter applications that require low cost, small size, high efficiency, and low noise. Full article
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Open AccessArticle
A Novel Three-Phase Six-Switch PFC Rectifier with Zero-Voltage-Switching and Zero-Current-Switching Features
Energies 2019, 12(6), 1119; https://doi.org/10.3390/en12061119 - 22 Mar 2019
Cited by 1
Abstract
A novel three-phase power-factor-correction (PFC) rectifier with zero-voltage-switching (ZVS) in six main switches and zero-current-switching (ZCS) in the auxiliary switch is proposed, analyzed, and experimentally verified. The main feature of the proposed auxiliary circuit is used to reduce the switching loss when the [...] Read more.
A novel three-phase power-factor-correction (PFC) rectifier with zero-voltage-switching (ZVS) in six main switches and zero-current-switching (ZCS) in the auxiliary switch is proposed, analyzed, and experimentally verified. The main feature of the proposed auxiliary circuit is used to reduce the switching loss when the six main switches are turned on and the one auxiliary switch is turned off. In this paper, a detailed operating analysis of the proposed circuit is given. Modeling and analysis are verified by experimental results based on a three-phase 7 kW rectifier. The soft-switched PFC rectifier shows an improvement in efficiency of 2.25% compared to its hard-switched counterpart at 220 V under full load. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1.Prof. Remus Teodorescu [email protected], Single Stage Photovoltaic Inverter using Modular Multilevel Converter with Multiple MPPT;

2.Prof. Dr. Dmitri Vinnikov [email protected],Inverters for single-phase grid connected photovoltaic systems;

3.Dr. Tuomas Messo [email protected], Grid-connected photovoltaic systems: An overview of recent research and emerging PV converter technology.

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