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Dr. Tamás Kerekes
Aalborg University, Department of Energy Technology

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0 Grid connected converter
0 Grid connected PV system
0 Photovoltaic grid-connected power generation system
0 DC-AC Power conversion
0 DC-AC Inverter

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Preprint content
Published: 26 July 2021
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A new Modular Multilevel Converter with Interleaved half-bridge Sub-Modules (ISM-MMC) is proposed in this paper. The ISM-MMC exhibits a higher modularity and scalability in terms of current ratings with respect to a conventional MMC, while preserves the typical voltage level adaptiveness. The ISM-MMC brings the known advantages of classical MMC to low-voltage, high-current applications making it a novel candidate for the sector of ultra-fast chargers for all types of electrical vehicles (EV). This advanced topology makes it possible to easily reach charging power of the EV charging system up to 4.5 MW and beyond with low-voltage supply. To operate the new converter, a hybrid modulation scheme that helps to exploit advantages of the interleaving scheme, is implemented, and explained in this paper. It has been verified that the typical MMC control methods are still applicable for ISM-MMC. A comparative study between classical MMC and ISM-MMC configurations in terms of output characteristics and efficiency is also given. Furthermore, it has been demonstrated that the number of ac voltage levels is synthetically multiplied by the number of interleaved half-bridge legs in submodules. Numerical simulations and Hardware-in-the-Loop tests are carried out to demonstrate the feasibility of the proposed topology and implemented modulation scheme.

ACS Style

Aleksandr Viatkin; Mattia Ricco; Riccardo Mandrioli; Tamas Kerekes; Remus Teodorescu; Gabriele Grandi. A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules. 2021, 1 .

AMA Style

Aleksandr Viatkin, Mattia Ricco, Riccardo Mandrioli, Tamas Kerekes, Remus Teodorescu, Gabriele Grandi. A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules. . 2021; ():1.

Chicago/Turabian Style

Aleksandr Viatkin; Mattia Ricco; Riccardo Mandrioli; Tamas Kerekes; Remus Teodorescu; Gabriele Grandi. 2021. "A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules." , no. : 1.

Preprint content
Published: 26 July 2021
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A new Modular Multilevel Converter with Interleaved half-bridge Sub-Modules (ISM-MMC) is proposed in this paper. The ISM-MMC exhibits a higher modularity and scalability in terms of current ratings with respect to a conventional MMC, while preserves the typical voltage level adaptiveness. The ISM-MMC brings the known advantages of classical MMC to low-voltage, high-current applications making it a novel candidate for the sector of ultra-fast chargers for all types of electrical vehicles (EV). This advanced topology makes it possible to easily reach charging power of the EV charging system up to 4.5 MW and beyond with low-voltage supply. To operate the new converter, a hybrid modulation scheme that helps to exploit advantages of the interleaving scheme, is implemented, and explained in this paper. It has been verified that the typical MMC control methods are still applicable for ISM-MMC. A comparative study between classical MMC and ISM-MMC configurations in terms of output characteristics and efficiency is also given. Furthermore, it has been demonstrated that the number of ac voltage levels is synthetically multiplied by the number of interleaved half-bridge legs in submodules. Numerical simulations and Hardware-in-the-Loop tests are carried out to demonstrate the feasibility of the proposed topology and implemented modulation scheme.

ACS Style

Aleksandr Viatkin; Mattia Ricco; Riccardo Mandrioli; Tamas Kerekes; Remus Teodorescu; Gabriele Grandi. A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules. 2021, 1 .

AMA Style

Aleksandr Viatkin, Mattia Ricco, Riccardo Mandrioli, Tamas Kerekes, Remus Teodorescu, Gabriele Grandi. A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules. . 2021; ():1.

Chicago/Turabian Style

Aleksandr Viatkin; Mattia Ricco; Riccardo Mandrioli; Tamas Kerekes; Remus Teodorescu; Gabriele Grandi. 2021. "A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules." , no. : 1.

Journal article
Published: 10 May 2021 in Electronics
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A reconfiguration technique using a switched-capacitor (SC)-based voltage equalizer differential power processing (DPP) concept is proposed in this paper for photovoltaic (PV) systems at a cell/subpanel/panel-level. The proposed active diffusion charge redistribution (ADCR) architecture increases the energy yield during mismatch and adds a voltage boosting capability to the PV system under no mismatch by connected the available PV cells/panels in series. The technique performs a reconfiguration by measuring the PV cell/panel voltages and their irradiances. The power balancing is achieved by charge redistribution through SC under mismatch conditions, e.g., partial shading. Moreover, PV cells/panels remain in series under no mismatch. Overall, this paper analyzes, simulates, and evaluates the effectiveness of the proposed DPP architecture through a simulation-based model prepared in PSIM. Additionally, the effectiveness is also demonstrated by comparing it with existing conventional DPP and traditional bypass diode architecture.

ACS Style

Kamran Niazi; Yongheng Yang; Tamas Kerekes; Dezso Sera. Reconfigurable Distributed Power Electronics Technique for Solar PV Systems. Electronics 2021, 10, 1121 .

AMA Style

Kamran Niazi, Yongheng Yang, Tamas Kerekes, Dezso Sera. Reconfigurable Distributed Power Electronics Technique for Solar PV Systems. Electronics. 2021; 10 (9):1121.

Chicago/Turabian Style

Kamran Niazi; Yongheng Yang; Tamas Kerekes; Dezso Sera. 2021. "Reconfigurable Distributed Power Electronics Technique for Solar PV Systems." Electronics 10, no. 9: 1121.

Journal article
Published: 04 May 2021 in IEEE Transactions on Power Electronics
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As the penetration of renewable energy generation increases, the importance of energy storage systems becomes evident since these systems can contribute to the preservation of the power system stability. Wind turbine owners can also benefit from having energy storage systems as they can increase their revenues. The fast growth of wind turbine power ratings will eventually lead to the requirement of higher voltage levels as well. Proper power-electronic converters will be required to drive these systems. Converters with a modular multilevel structure are considered the state-of-the-art solution for high-power applications. These topologies allow for a flexible integration of energy storage systems in both centralized and decentralized ways. This paper presents a new converter solution with a modular multilevel structure and decentralized energy storage integration suitable to drive high-power medium-voltage wind turbines. This converter presents important structural and control characteristics that allow for straightforward integration of an energy storage system in such a way that the wind turbine driven by it can operate with high flexibility and in a dispatchable fashion, benefiting both the power system operator and the wind-power-plant owner.

ACS Style

Gustavo F. Gontijo; Tamas Kerekes; Dezso Sera; Mattia Ricco; Laszlo Mathe; Remus Teodorescu. Medium-Voltage Converter Solution With Modular Multilevel Structure and Decentralized Energy Storage Integration for High-Power Wind Turbines. IEEE Transactions on Power Electronics 2021, 36, 12954 -12967.

AMA Style

Gustavo F. Gontijo, Tamas Kerekes, Dezso Sera, Mattia Ricco, Laszlo Mathe, Remus Teodorescu. Medium-Voltage Converter Solution With Modular Multilevel Structure and Decentralized Energy Storage Integration for High-Power Wind Turbines. IEEE Transactions on Power Electronics. 2021; 36 (11):12954-12967.

Chicago/Turabian Style

Gustavo F. Gontijo; Tamas Kerekes; Dezso Sera; Mattia Ricco; Laszlo Mathe; Remus Teodorescu. 2021. "Medium-Voltage Converter Solution With Modular Multilevel Structure and Decentralized Energy Storage Integration for High-Power Wind Turbines." IEEE Transactions on Power Electronics 36, no. 11: 12954-12967.

Journal article
Published: 19 April 2021 in Energies
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Partial shading affects the energy harvested from photovoltaic (PV) modules, leading to a mismatch in PV systems and causing energy losses. For this purpose, differential power processing (DPP) converters are the emerging power electronic-based topologies used to address the mismatch issues. Normally, PV modules are connected in series and DPP converters are used to extract the power from these PV modules by only processing the fraction of power called mismatched power. In this work, a switched-capacitor-inductor (SCL)-based DPP converter is presented, which mitigates the non-ideal conditions in solar PV systems. A proposed SCL-based DPP technique utilizes a simple control strategy to extract the maximum power from the partially shaded PV modules by only processing a fraction of the power. Furthermore, an operational principle and loss analysis for the proposed converter is presented. The proposed topology is examined and compared with the traditional bypass diode technique through simulations and experimental tests. The efficiency of the proposed DPP is validated by the experiment and simulation. The results demonstrate the performance in terms of higher energy yield without bypassing the low-producing PV module by using a simple control. The results indicate that achieved efficiency is higher than 98% under severe mismatch (higher than 50%).

ACS Style

Kamran Niazi; Yongheng Yang; Tamas Kerekes; Dezso Sera. A Simple Mismatch Mitigating Partial Power Processing Converter for Solar PV Modules. Energies 2021, 14, 2308 .

AMA Style

Kamran Niazi, Yongheng Yang, Tamas Kerekes, Dezso Sera. A Simple Mismatch Mitigating Partial Power Processing Converter for Solar PV Modules. Energies. 2021; 14 (8):2308.

Chicago/Turabian Style

Kamran Niazi; Yongheng Yang; Tamas Kerekes; Dezso Sera. 2021. "A Simple Mismatch Mitigating Partial Power Processing Converter for Solar PV Modules." Energies 14, no. 8: 2308.

Journal article
Published: 29 March 2021 in Energies
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Satisfying the mobile traffic demand in next generation cellular networks increases the cost of energy supply. Renewable energy sources are a promising solution to power base stations in a self-sufficient and cost-effective manner. This paper presents an optimal method for designing a photovoltaic (PV)-battery system to supply base stations in cellular networks. A systematic approach is proposed for determining the power rating of the photovoltaic generator and battery capacity from a technical and economical point of view in order to minimize investment cost as well as operational expenditure, while the power autonomy of the PV-battery system is maximized in a multi-objective optimization framework. The proposed method is applied to optimally size a photovoltaic-battery system for three cases with different availability of solar power to investigate the effect of environmental conditions. Problem-solving using the proposed approach leads to a set of solutions at different costs versus different levels of power autonomy. According to the importance of each criterion and the preference of decision-makers, one of the achieved solutions can be selected for the implementation of the photovoltaic-battery system to supply base stations in cellular networks.

ACS Style

Mahshid Javidsharifi; Hamoun Pourroshanfekr; Tamas Kerekes; Dezso Sera; Sergiu Spataru; Josep Guerrero. Optimum Sizing of Photovoltaic and Energy Storage Systems for Powering Green Base Stations in Cellular Networks. Energies 2021, 14, 1895 .

AMA Style

Mahshid Javidsharifi, Hamoun Pourroshanfekr, Tamas Kerekes, Dezso Sera, Sergiu Spataru, Josep Guerrero. Optimum Sizing of Photovoltaic and Energy Storage Systems for Powering Green Base Stations in Cellular Networks. Energies. 2021; 14 (7):1895.

Chicago/Turabian Style

Mahshid Javidsharifi; Hamoun Pourroshanfekr; Tamas Kerekes; Dezso Sera; Sergiu Spataru; Josep Guerrero. 2021. "Optimum Sizing of Photovoltaic and Energy Storage Systems for Powering Green Base Stations in Cellular Networks." Energies 14, no. 7: 1895.

Journal article
Published: 02 February 2021 in Energies
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The modular multilevel converter is capable to reach high-voltage levels with high flexibility, high reliability, and high power quality as it became the standard solution for high-power high-voltage applications that operate with fixed frequency. However, in machine-drive applications, the modular multilevel converter shows critical problems since an extremely high submodule-capacitor voltage ripple occurs in the machine start-up and at low-speed operation, which can damage the converter. Recently, a new converter solution named modular multilevel series converter was proposed as a promising alternative for high-power machine-drive applications since it presented many important structural and operational advantages in relation to the modular multilevel converter such as the reduced number of submodule capacitors and the low submodule-capacitor voltage ripple at low frequencies. Even though the modular multilevel series converter presented a reduced number of capacitors, the size of these capacitors was not analyzed. This paper presents a detailed comparison analysis of the performance of the modular multilevel converter and the modular multilevel series converter at variable-frequency operation, which is based on the proposed analytical description of the submodule-capacitor voltage ripple in such topologies. This analysis concludes that the new modular multilevel series converter can be designed with smaller capacitors in comparison to the modular multilevel converter if these converters are used to drive electrical machines that operate within a range of low-frequency values. In other words, the modular multilevel series converter experiences extremely low submodule-capacitor voltage ripple at very low frequencies, which means that this converter solution presents high performance in the electrical machine start-up and at low-speed operation.

ACS Style

Gustavo Gontijo; Songda Wang; Tamas Kerekes; Remus Teodorescu. Performance Analysis of Modular Multilevel Converter and Modular Multilevel Series Converter under Variable-Frequency Operation Regarding Submodule-Capacitor Voltage Ripple. Energies 2021, 14, 776 .

AMA Style

Gustavo Gontijo, Songda Wang, Tamas Kerekes, Remus Teodorescu. Performance Analysis of Modular Multilevel Converter and Modular Multilevel Series Converter under Variable-Frequency Operation Regarding Submodule-Capacitor Voltage Ripple. Energies. 2021; 14 (3):776.

Chicago/Turabian Style

Gustavo Gontijo; Songda Wang; Tamas Kerekes; Remus Teodorescu. 2021. "Performance Analysis of Modular Multilevel Converter and Modular Multilevel Series Converter under Variable-Frequency Operation Regarding Submodule-Capacitor Voltage Ripple." Energies 14, no. 3: 776.

Journal article
Published: 10 December 2020 in Applied Sciences
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A wide range of defects, failures, and degradation can develop at different stages in the lifetime of photovoltaic modules. To accurately assess their effect on the module performance, these failures need to be quantified. Electroluminescence (EL) imaging is a powerful diagnostic method, providing high spatial resolution images of solar cells and modules. EL images allow the identification and quantification of different types of failures, including those in high recombination regions, as well as series resistance-related problems. In this study, almost 46,000 EL cell images are extracted from photovoltaic modules with different defects. We present a method that extracts statistical parameters from the histogram of these images and utilizes them as a feature descriptor. Machine learning algorithms are then trained using this descriptor to classify the detected defects into three categories: (i) cracks (Mode B and C), (ii) micro-cracks (Mode A) and finger failures, and (iii) no failures. By comparing the developed methods with the commonly used one, this study demonstrates that the pre-processing of images into a feature vector of statistical parameters provides a higher classification accuracy than would be obtained by raw images alone. The proposed method can autonomously detect cracks and finger failures, enabling outdoor EL inspection using a drone-mounted system for quick assessments of photovoltaic fields.

ACS Style

Harsh Rajesh Parikh; Yoann Buratti; Sergiu Spataru; Frederik Villebro; Gisele Alves Dos Reis Benatto; Peter B. Poulsen; Stefan Wendlandt; Tamas Kerekes; Dezso Sera; Ziv Hameiri. Solar Cell Cracks and Finger Failure Detection Using Statistical Parameters of Electroluminescence Images and Machine Learning. Applied Sciences 2020, 10, 8834 .

AMA Style

Harsh Rajesh Parikh, Yoann Buratti, Sergiu Spataru, Frederik Villebro, Gisele Alves Dos Reis Benatto, Peter B. Poulsen, Stefan Wendlandt, Tamas Kerekes, Dezso Sera, Ziv Hameiri. Solar Cell Cracks and Finger Failure Detection Using Statistical Parameters of Electroluminescence Images and Machine Learning. Applied Sciences. 2020; 10 (24):8834.

Chicago/Turabian Style

Harsh Rajesh Parikh; Yoann Buratti; Sergiu Spataru; Frederik Villebro; Gisele Alves Dos Reis Benatto; Peter B. Poulsen; Stefan Wendlandt; Tamas Kerekes; Dezso Sera; Ziv Hameiri. 2020. "Solar Cell Cracks and Finger Failure Detection Using Statistical Parameters of Electroluminescence Images and Machine Learning." Applied Sciences 10, no. 24: 8834.

Journal article
Published: 08 December 2020 in IEEE Transactions on Power Electronics
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The quasi-Z-source inverter (qZSI) has been widely explored for renewable energy applications due to its superiority. As a conventional space vector modulation (SVM) method for the three-phase qZSI, the ZSVM6 method is easy to implement by dividing the ST time into six identical intervals. However, the instantaneous inductor current ripples of the qZSI with the ZSVM6 strategy are affected by the operating conditions. In this paper, the instantaneous inductor current ripples and the maximum current ripple in the qZSI with the ZSVM6 strategy under all operational conditions are explored in detail. More importantly, an improved ZSVM6 strategy is proposed to reduce the inductor current ripple for the qZSI, in which the maximum inductor current ripple is limited by making full use of the operational states. Simulations and experimental results confirm effectiveness of the proposal when compared with the conventional ZSVM6 strategy for ripple current reduction.

ACS Style

Wenjie Liu; Yongheng Yang; Tamas Kerekes; Dmitri Vinnikov; Frede Blaabjerg. Inductor Current Ripple Analysis and Reduction for Quasi-Z-Source Inverters With an Improved ZSVM6 Strategy. IEEE Transactions on Power Electronics 2020, 36, 7693 -7704.

AMA Style

Wenjie Liu, Yongheng Yang, Tamas Kerekes, Dmitri Vinnikov, Frede Blaabjerg. Inductor Current Ripple Analysis and Reduction for Quasi-Z-Source Inverters With an Improved ZSVM6 Strategy. IEEE Transactions on Power Electronics. 2020; 36 (7):7693-7704.

Chicago/Turabian Style

Wenjie Liu; Yongheng Yang; Tamas Kerekes; Dmitri Vinnikov; Frede Blaabjerg. 2020. "Inductor Current Ripple Analysis and Reduction for Quasi-Z-Source Inverters With an Improved ZSVM6 Strategy." IEEE Transactions on Power Electronics 36, no. 7: 7693-7704.

Journal article
Published: 04 December 2020 in Applied Sciences
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In transformerless grid-connected photovoltaic (PV) systems, leakage currents should be properly addressed. The voltage fluctuations between the neutral point of the grid and the PV array, i.e., common-mode voltage (CMV), will affect the value of the leakage currents. Therefore, the leakage currents can be attenuated through proper control of the CMV. The CMV depends on the converter topology and the modulation strategy. For the quasi-Z-source inverter (qZSI), the amplitude of the high-frequency components in the CMV increases due to the extra shoot-through (ST) state. The CMV reduction strategies for the conventional voltage source inverter (VSI) should be modified when applied to the qZSI. In this paper, an input-split-inductor qZSI is introduced to reduce the CMV, in which all the CMV reduction strategies for the VSI can be used directly with appropriate ST state insertion. Moreover, the proposed method can be extended to impedance source converters with a similar structure. Simulations and experimental tests demonstrate the effectiveness of the proposed strategy for the qZSI in terms of CMV reduction.

ACS Style

Wenjie Liu; Yongheng Yang; Tamas Kerekes; Elizaveta Liivik; Dmitri Vinnikov; Frede Blaabjerg. Common-Mode Voltage Analysis and Reduction for the Quasi-Z-Source Inverter with a Split Inductor. Applied Sciences 2020, 10, 8713 .

AMA Style

Wenjie Liu, Yongheng Yang, Tamas Kerekes, Elizaveta Liivik, Dmitri Vinnikov, Frede Blaabjerg. Common-Mode Voltage Analysis and Reduction for the Quasi-Z-Source Inverter with a Split Inductor. Applied Sciences. 2020; 10 (23):8713.

Chicago/Turabian Style

Wenjie Liu; Yongheng Yang; Tamas Kerekes; Elizaveta Liivik; Dmitri Vinnikov; Frede Blaabjerg. 2020. "Common-Mode Voltage Analysis and Reduction for the Quasi-Z-Source Inverter with a Split Inductor." Applied Sciences 10, no. 23: 8713.

Research article
Published: 01 December 2020 in IET Power Electronics
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This study proposes a high step-up DC–DC converter which is composed of a conventional quadratic boost converter, a switched capacitor and a coupled inductor. To reduce the number of components, the primary side of the coupled inductor is shared with the quadratic boost converter as one of its inductors. Furthermore, the output capacitor of the quadratic boost converter is divided into two capacitors and one of them is utilised in common with the switched capacitor. The converter is analysed and the obtained equations are used to compare the proposed converter with other converters which have similar structures. According to the comparisons, the proposed converter has advantages such as higher voltage gain, the lower voltage stress on the power switch and requiring a smaller inductor. In addition, the input source current is continuous and there is a common ground between the source and load. Increasing the turn ratio of the coupled inductor causes reduction of voltage stress on the power switch, diodes and capacitors. To investigate performance of the proposed converter, an 80 W prototype is built. The experiments show good accordance with the analysis and they demonstrate the high step-up capability of the proposed converter.

ACS Style

Milad Rezaie; Vahid Abbasi; Tamas Kerekes. High step‐up DC–DC converter composed of quadratic boost converter and switched capacitor. IET Power Electronics 2020, 13, 4008 -4018.

AMA Style

Milad Rezaie, Vahid Abbasi, Tamas Kerekes. High step‐up DC–DC converter composed of quadratic boost converter and switched capacitor. IET Power Electronics. 2020; 13 (17):4008-4018.

Chicago/Turabian Style

Milad Rezaie; Vahid Abbasi; Tamas Kerekes. 2020. "High step‐up DC–DC converter composed of quadratic boost converter and switched capacitor." IET Power Electronics 13, no. 17: 4008-4018.

Journal article
Published: 09 October 2020 in IEEE Transactions on Power Electronics
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An increasing intake of grid-connected inverters could change the characteristics of low voltage networks including the equivalent grid impedance. This can impact the overall performance of the inverters, thus it becomes necessary for grid-connected inverters to estimate the grid impedance online. However, there are some challenges when it comes to grid impedance estimation using grid-connected inverters. These include the estimation accuracy and the associated power quality issues that are mainly related to the amplitude, frequency and period of the injected disturbance into the grid. To address these challenges, a novel online event-based grid impedance estimation technique for grid-connected inverters is proposed in this paper. This technique combines an active grid impedance estimation technique, based on variations of the inverter's output power, and the continuous monitoring of the positive-sequence amplitude of the PCC voltage. The main advantage is that the estimation technique only performs a deliberate perturbation of P and Q if there is a certain change in voltage magnitude related to grid impedance change. This significantly reduces the occurrence of required PQ variations, thus minimizing the power losses and the impact on power quality. Simulation and experimental results of a grid-connected inverter system validate the performance of the proposed technique.

ACS Style

Nabil Mohammed; Tamas Kerekes; Mihai Ciobotaru. An Online Event-Based Grid Impedance Estimation Technique Using Grid-Connected Inverters. IEEE Transactions on Power Electronics 2020, 36, 6106 -6117.

AMA Style

Nabil Mohammed, Tamas Kerekes, Mihai Ciobotaru. An Online Event-Based Grid Impedance Estimation Technique Using Grid-Connected Inverters. IEEE Transactions on Power Electronics. 2020; 36 (5):6106-6117.

Chicago/Turabian Style

Nabil Mohammed; Tamas Kerekes; Mihai Ciobotaru. 2020. "An Online Event-Based Grid Impedance Estimation Technique Using Grid-Connected Inverters." IEEE Transactions on Power Electronics 36, no. 5: 6106-6117.

Journal article
Published: 30 July 2020 in IEEE Journal of Photovoltaics
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This article proposes an improved maximum power point tracking (MPPT) method that features a simple design, and improved efficiency in fast-changing irradiance conditions. The method uses three consecutive measurements and compares the power difference between each two consecutive samples, furthermore the voltage variation between the last two successive samples is observed. According to the obtained result of these comparisons, the algorithm applies the suitable action either increasing or decreasing the voltage. This simple concept allows easy implementation and reduces the implementation cost and calculation burden. Second, the method has a prompt tracking response during fast changes in solar irradiance (e.g., due to passing clouds). The proposed method is validated through experimental tests using solar irradiance profiles according to the EN50530 standard and is compared to the classical Perturb and Observe method. The experimental results show that the proposed MPPT effectively identifies the change in solar irradiance, and maintains high tracking efficiency even in fast-changing conditions.

ACS Style

Hafsa Abouadane; Abderrahim Fakkar; Dezso Sera; Abderezak Lashab; Sergiu Spataru; Tamas Kerekes. Multiple-Power-Sample Based P&O MPPT for Fast-Changing Irradiance Conditions for a Simple Implementation. IEEE Journal of Photovoltaics 2020, 10, 1481 -1488.

AMA Style

Hafsa Abouadane, Abderrahim Fakkar, Dezso Sera, Abderezak Lashab, Sergiu Spataru, Tamas Kerekes. Multiple-Power-Sample Based P&O MPPT for Fast-Changing Irradiance Conditions for a Simple Implementation. IEEE Journal of Photovoltaics. 2020; 10 (5):1481-1488.

Chicago/Turabian Style

Hafsa Abouadane; Abderrahim Fakkar; Dezso Sera; Abderezak Lashab; Sergiu Spataru; Tamas Kerekes. 2020. "Multiple-Power-Sample Based P&O MPPT for Fast-Changing Irradiance Conditions for a Simple Implementation." IEEE Journal of Photovoltaics 10, no. 5: 1481-1488.

Journal article
Published: 20 July 2020 in IEEE Transactions on Power Electronics
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This paper proposes a generalized space vector modulation (SVM) strategy for the three-phase quasi-Z-source inverter (qZSI), which can reduce the inductor current ripples by limiting the peaks in different sectors of the vector space. In the conventional ZSVM6 strategy, the shoot-through interval is divided into six equal parts, which is easy to implement. However, the inductor current ripples are not optimized. Generally, larger inductance is required to limit the current ripples, resulting in poor power density. By contrast, the proposed SVM strategy can minimize the current ripple, while maintaining the same total shoot-through time. Although the shoot-through intervals in the proposed SVM strategy are not identical, it is still easy to implement. The generalized strategy can ensure that the inductor current ripples are always smaller than the peak of the inductor discharging current ripple in a switching cycle. The proposed SVM strategy is derived in details and compared with the conventional ZSVM6 strategy. Simulation and experimental results are presented to verify the effectiveness of the proposed modulation strategy for inductor ripple current reduction.

ACS Style

Wenjie Liu; Yongheng Yang; Tamas Kerekes; Frede Blaabjerg. Generalized Space Vector Modulation for Ripple Current Reduction in Quasi-Z-Source Inverters. IEEE Transactions on Power Electronics 2020, 36, 1730 -1741.

AMA Style

Wenjie Liu, Yongheng Yang, Tamas Kerekes, Frede Blaabjerg. Generalized Space Vector Modulation for Ripple Current Reduction in Quasi-Z-Source Inverters. IEEE Transactions on Power Electronics. 2020; 36 (2):1730-1741.

Chicago/Turabian Style

Wenjie Liu; Yongheng Yang; Tamas Kerekes; Frede Blaabjerg. 2020. "Generalized Space Vector Modulation for Ripple Current Reduction in Quasi-Z-Source Inverters." IEEE Transactions on Power Electronics 36, no. 2: 1730-1741.

Journal article
Published: 16 July 2020 in Energies
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Due to its scalability, reliability, high power quality and flexibility, the modular multilevel converter is the standard solution for high-power high-voltage applications in which an AC–DC–AC connection is required such as high-voltage direct-current transmission systems. However, this converter presents some undesired features from both structural and operational perspectives. For example, it presents a high number of components, which results in high costs, size, weight and conduction losses. Moreover, the modular multilevel converter presents problems dealing with DC-side faults, with unbalanced grid conditions, and many internal control loops are required for its proper operation. In variable-frequency operation, the modular multilevel converter presents some serious limitations. The most critical are the high-voltage ripples, in the submodule capacitors, at low frequencies. Thus, many different AC–AC converter solutions, with modular multilevel structure, have been proposed as alternatives for high-power machine-drive applications such as offshore wind turbines, pumped-hydro-storage systems and industrial motor drives. These converters present their own drawbacks mostly related to control complexity, operational limitations, size and weight. This paper introduces an entirely new medium-voltage AC–AC modular multilevel converter solution with many operational and structural advantages in comparison to the modular multilevel converter and other alternative topologies. The proposed converter presents high performance at low frequencies, regarding the amplitude of the voltage ripples in the submodule capacitors, which could make it very suitable for machine-drive applications. In this paper, an analytical description of the voltage ripples in the submodule capacitors is proposed, which proves the high performance of the converter under low-frequency operation. Moreover, the proposed converter presents high performance under unbalanced grid conditions. This important feature is demonstrated through simulation results. The converter solution introduced in this paper has a simple structure, with decoupled phases, which leads to the absence of undesired circulating currents and to a straightforward control, with very few internal control loops for its proper operation, and with simple modulation. Since the converter phases are decoupled, no arm inductors are required, which contributes to the weight and size reduction of the topology. In this paper, a detailed comparison analysis with the modular multilevel converter is presented based on number of components, conduction and switching losses. This analysis concludes that the proposed converter solution presents a reduction in costs and an expressive reduction in size and weight, in comparison to the modular multilevel converter. Thus, it should be a promising solution for high-power machine-drive applications that require compactness and lightness such as offshore wind turbines. In this paper, simulation results are presented explaining the behavior of the proposed converter, proving that it is capable of synthesizing a high-power-quality load voltage, with variable frequency, while exchanging power with the grid. Thus, this topology could be used to control the machine speed in a machine-drive application. Finally, experimental results are provided to validate the topology.

ACS Style

Gustavo Gontijo; Songda Wang; Tamas Kerekes; Remus Teodorescu. New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter. Energies 2020, 13, 3664 .

AMA Style

Gustavo Gontijo, Songda Wang, Tamas Kerekes, Remus Teodorescu. New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter. Energies. 2020; 13 (14):3664.

Chicago/Turabian Style

Gustavo Gontijo; Songda Wang; Tamas Kerekes; Remus Teodorescu. 2020. "New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter." Energies 13, no. 14: 3664.

Journal article
Published: 09 June 2020 in IEEE Transactions on Power Electronics
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This letter proposes a multilevel inverter (MLI), which can be considered to be belonging to the cascaded H-bridge (CHB) family. In the proposed MLI, some of the H-bridges are connected to dc-sources, while most of the H-bridges are connected to only floating capacitors. A boosting circuit is integrated in the CHB, which permits charging the floating capacitors, enabling a higher voltage at the inverter's output with respect to the dc-sources total one. This boosting feature is essential in some applications like photovoltaic and fuel cell systems. Compared to the popular solutions in the literature, the proposal still offers a high boosting ratio with fewer employed components. A prototype of the proposed MLI has been built, and the results confirming its validity are shown in this letter. Efficiency analysis and evaluation with respect to one of the conventional solutions is also presented, where it is demonstrated that the proposal shows an improvement of 3.94% according to the European efficiency.

ACS Style

Abderezak Lashab; Dezso Sera; Tamas Kerekes; Yacine Terriche; Aissa Bouzid; Juan C. Vasquez; Josep M. Guerrero. A Cascaded H-Bridge With Integrated Boosting Circuit. IEEE Transactions on Power Electronics 2020, 36, 18 -22.

AMA Style

Abderezak Lashab, Dezso Sera, Tamas Kerekes, Yacine Terriche, Aissa Bouzid, Juan C. Vasquez, Josep M. Guerrero. A Cascaded H-Bridge With Integrated Boosting Circuit. IEEE Transactions on Power Electronics. 2020; 36 (1):18-22.

Chicago/Turabian Style

Abderezak Lashab; Dezso Sera; Tamas Kerekes; Yacine Terriche; Aissa Bouzid; Juan C. Vasquez; Josep M. Guerrero. 2020. "A Cascaded H-Bridge With Integrated Boosting Circuit." IEEE Transactions on Power Electronics 36, no. 1: 18-22.

Review
Published: 23 September 2019 in Energies
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Photovoltaic (PV) energy has been competitive in power generation as an alternative to fossil energy resources over the past decades. The installation of grid-connected solar energy systems is expected to increase rapidly with the fast development of the power electronics technology. As the key to the interface of the PV energy and the grid, power converters should be reliable, efficient and comply with the grid requirements. Considering the nature of PV energy, the power conversion should be flexible (e.g., high step-up DC-DC conversion and harmonic-free DC-AC conversion). Accordingly, many power electronic converters have been reported in literature. Compared with isolated inverters, transformerless inverters show great advantages. This paper thus presents an overview of the transformerless step-up single-phase inverters for PV applications based on the dc-link configurations. Grid-connected PV inverters are classified as constant dc-link voltage structures, pseudo-dc-link voltage structures, pulsating dc-link voltage structures and integrated dc-link voltage structures. The discussion on the composition of different dc-link structures is presented, which provides guidance to select appropriate transformerless inverter topologies for PV applications.

ACS Style

Wenjie Liu; Kamran Ali Khan Niazi; Tamas Kerekes; Yongheng Yang. A Review on Transformerless Step-Up Single-Phase Inverters with Different DC-Link Voltage for Photovoltaic Applications. Energies 2019, 12, 3626 .

AMA Style

Wenjie Liu, Kamran Ali Khan Niazi, Tamas Kerekes, Yongheng Yang. A Review on Transformerless Step-Up Single-Phase Inverters with Different DC-Link Voltage for Photovoltaic Applications. Energies. 2019; 12 (19):3626.

Chicago/Turabian Style

Wenjie Liu; Kamran Ali Khan Niazi; Tamas Kerekes; Yongheng Yang. 2019. "A Review on Transformerless Step-Up Single-Phase Inverters with Different DC-Link Voltage for Photovoltaic Applications." Energies 12, no. 19: 3626.

Research article
Published: 23 September 2019 in IET Power Electronics
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This study proposes a common grounded Z-source DC–DC converter. In comparison to conventional Z-source converter, it converts voltage with higher voltage gain and lower voltage stress on the switch, diodes and capacitors. In addition, it needs smaller inductors in comparison to the similar converters. The converter is analysed and compared with other converters. Its main equations are obtained which show the converter advantages as lower voltage stresses, smaller inductors, higher efficiency and higher voltage gain in comparison to the reviewed converters. A prototype for the proposed converter is prepared based on analysis and theoretical parts. Experiments are done along the lines of the analysis. Experimental results and theoretical equations are used to prove the converter operation quality.

ACS Style

Sajad Rostami; Vahid Abbasi; Tamas Kerekes. Switched capacitor based Z‐source DC–DC converter. IET Power Electronics 2019, 12, 3582 -3589.

AMA Style

Sajad Rostami, Vahid Abbasi, Tamas Kerekes. Switched capacitor based Z‐source DC–DC converter. IET Power Electronics. 2019; 12 (13):3582-3589.

Chicago/Turabian Style

Sajad Rostami; Vahid Abbasi; Tamas Kerekes. 2019. "Switched capacitor based Z‐source DC–DC converter." IET Power Electronics 12, no. 13: 3582-3589.

Journal article
Published: 09 April 2019 in IEEE Journal of Emerging and Selected Topics in Power Electronics
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In photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations between input and output. However, these conventional iron and copper-based transformers increase the weight/size and cost of the inverter whilst reducing the efficiency and power density. It is therefore desirable to avoid using transformers in the inverter. However, additional care must be taken to avoid safety hazards such as ground fault currents and leakage currents, e.g. via the parasitic capacitor between the PV panel and ground. Consequently, the grid connected transformerless PV inverters must comply with strict safety standards such as IEEE 1547.1, VDE0126-1-1, EN 50106, IEC61727, and AS/NZS 5033. Various transformerless inverters have been proposed recently to eliminate the leakage current using different techniques such as decoupling the DC from the AC side and/or clamping the common mode (CM) voltage during the freewheeling period, or using common ground configurations. The permutations and combinations of various decoupling techniques with integrated voltage buck-boost for maximum power point tracking (MPPT) allow numerous new topologies and configurations which are often confusing and difficult to follow when seeking to select the right topology. Therefore, to present a clear picture on the development of transformerless inverters for the next generation grid-connected PV systems, this paper aims to comprehensively review and classify various transformerless inverters with detailed analytical comparisons. To reinforce the findings and comparisons as well as to give more insight on the CM characteristics and leakage current, computer simulations of major transformerless inverter topologies have been performed in PLECS software. Moreover, the cost and size are analysed properly and summarized in a table. Finally, efficiency and thermal analysis are provided with a general summary as well as a technology roadmap.

ACS Style

Noman H. Khan; Mojtaba Forouzesh; Yam P. Siwakoti; Li Li; Tamas Kerekes; Frede Blaabjerg. Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems: A Comparative Review. IEEE Journal of Emerging and Selected Topics in Power Electronics 2019, 8, 805 -835.

AMA Style

Noman H. Khan, Mojtaba Forouzesh, Yam P. Siwakoti, Li Li, Tamas Kerekes, Frede Blaabjerg. Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems: A Comparative Review. IEEE Journal of Emerging and Selected Topics in Power Electronics. 2019; 8 (1):805-835.

Chicago/Turabian Style

Noman H. Khan; Mojtaba Forouzesh; Yam P. Siwakoti; Li Li; Tamas Kerekes; Frede Blaabjerg. 2019. "Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems: A Comparative Review." IEEE Journal of Emerging and Selected Topics in Power Electronics 8, no. 1: 805-835.

Journal article
Published: 28 February 2019 in Energies
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The economic viability of renewable energy generation is vital for sustainability. Ensuring that optimal operation is always achieved, using energy management systems and control algorithms, is essential in this endeavor. Here, a new real-time pricing scheme, the Danish flexible pricing scheme, illustrates how residential PV and battery systems can optimize the electricity bill of households, without changing consumption behavior or providing grid services in exchange. This means that the only addition is PV production, storage, and control. A case study is constructed from Danish household consumption data, irradiance measurements, and recorded spot prices. With the input data, the pricing scheme, and the energy flow, simulation models are computed in MATLAB, thereby validating the algorithmic potential and finding the best strategy for charging and discharging the energy storage unit. Different methods are compared to list the viable options and evaluate them, based on the economic feasibility for the household. Furthermore, a discussion of the system implementation is also included to highlight technical difficulties, co-integration opportunities, short-comings, and advantages present in the case study. In conclusion, it is possible to make renewable energy generation, and storage, viable for a Danish residential household under the new pricing scheme.

ACS Style

Jacob Bitsch Nørgaard; Tamás Kerekes; Dezso Séra. Case Study of Residential PV Power and Battery Storage with the Danish Flexible Pricing Scheme. Energies 2019, 12, 799 .

AMA Style

Jacob Bitsch Nørgaard, Tamás Kerekes, Dezso Séra. Case Study of Residential PV Power and Battery Storage with the Danish Flexible Pricing Scheme. Energies. 2019; 12 (5):799.

Chicago/Turabian Style

Jacob Bitsch Nørgaard; Tamás Kerekes; Dezso Séra. 2019. "Case Study of Residential PV Power and Battery Storage with the Danish Flexible Pricing Scheme." Energies 12, no. 5: 799.