Double Boost Power-Decoupling Topology Suitable for Low-Voltage Photovoltaic Residential Applications Using Sliding-Mode Impedance-Shaping Controller

Tawfik, Mohamed Atef,Ahmed, Ashraf,Park, Joung-Hu The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4

This paper proposes a practical sliding-mode controller design for shaping the impedances of cascaded boost-converter power decoupling circuits for reducing the second order harmonic ripple in photovoltaic (PV) current. The cascaded double-boost converter, when used as power decoupling circuit, has some advantages in terms of a high step-up voltage-ratio, a small number of switches and a better efficiency when compared to conventional topologies. From these features, it can be seen that this topology is suitable for residential (PV) rooftop systems. However, a robust controller design capable of rejecting double frequency inverter ripple from passing to the (PV) source is a challenge. The design constraints are related to the principle of the impedance-shaping technique to maximize the output impedance of the input-side boost converter, to block the double frequency PV current ripple component, and to prevent it from passing to the source without degrading the system dynamic responses. The design has a small recovery time in the presence of transients with a low overshoot or undershoot. Moreover, the proposed controller ensures that the ripple component swings freely within a voltage-gap between the (PV) and the DC-link voltages by the small capacitance of the auxiliary DC-link for electrolytic-capacitor elimination. The second boost controls the main DC-link voltage tightly within a satisfactory ripple range. The inverter controller performs maximum power point tracking (MPPT) for the input voltage source using ripple correlation control (RCC). The robustness of the proposed control was verified by varying system parameters under different load conditions. Finally, the proposed controller was verified by simulation and experimental results.

Double Boost Power-Decoupling Topology Suitable for Low-Voltage Photovoltaic Residential Applications Using Sliding-Mode Impedance-Shaping Controller

Mohamed Atef Tawfik,Ashraf Ahmed,박종후 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4

This paper proposes a practical sliding-mode controller design for shaping the impedances of cascaded boost-converter powerdecoupling circuits for reducing the second order harmonic ripple in photovoltaic (PV) current. The cascaded double-boostconverter, when used as power decoupling circuit, has some advantages in terms of a high step-up voltage-ratio, a small numberof switches and a better efficiency when compared to conventional topologies. From these features, it can be seen that thistopology is suitable for residential (PV) rooftop systems. However, a robust controller design capable of rejecting double frequencyinverter ripple from passing to the (PV) source is a challenge. The design constraints are related to the principle of the impedanceshapingtechnique to maximize the output impedance of the input-side boost converter, to block the double frequency PV currentripple component, and to prevent it from passing to the source without degrading the system dynamic responses. The design hasa small recovery time in the presence of transients with a low overshoot or undershoot. Moreover, the proposed controllerensures that the ripple component swings freely within a voltage-gap between the (PV) and the DC-link voltages by the smallcapacitance of the auxiliary DC-link for electrolytic-capacitor elimination. The second boost controls the main DC-link voltagetightly within a satisfactory ripple range. The inverter controller performs maximum power point tracking (MPPT) for the inputvoltage source using ripple correlation control (RCC). The robustness of the proposed control was verified by varying systemparameters under different load conditions. Finally, the proposed controller was verified by simulation and experimental results.

Capacitor‑less modular multilevel converter with sliding mode control for MV adjustable‑speed motor drives

Mohamed Atef Tawfik,Mohammad Sameer Irfan,Chungu Lee,Ashraf Ahmed,Joung-Hu Park 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.8

Medium-voltage (MV) motor drives have become an appealing application for modular multilevel converters (MMCs). Starting and operation at low speeds result in wide fluctuations of the low-frequency ripple components in the sub-module (SM) capacitors DC link voltages, which can adversely affect system performance and system lifetime. A solution for this problem is to replace the low-frequency (LF) SM capacitor with a power decoupling circuit (PDC) that is independent from the converter line frequency. In this paper, a power decoupling approach based on the flux cancelation method is proposed. A three-winding high-frequency transformer (HFT) is employed to magnetically couple and cancel the three-phase symmetrical ripple power. However, this approach has two main challenges. (1) The ripple powers through the HFT are a function of the value of the leakage inductances. (2) Different leakage inductances and ripple power unbalance between phases cause unequal ripple voltages. As a result, phase-shift ripple rejection control is needed. Conventional liner controllers have several problems, such as bandwidth limitations, stability margins, and slow dynamics near-zero-speed operation. In addition, linear controllers are designed for a specific ripple frequency. In this paper, a frequency-independent ripple rejection sliding mode controller (SMC) is proposed to overcome the limitations of linear controllers. The SMC is applied to pass the SM capacitor voltage ripple into the HFT. Thus, the ripple is canceled out in the HFT magnetic core regardless of the converter line frequency. The proposed control is suitable for adjustable-speed applications. The performance of the proposed scheme is verified via simulation and experimental tests.

Electrolytic capacitorless STATCOM with both inductive and capacitive VAR compensation modes

Mohammad Sameer Irfan,Young-Tae Jeon,Mohamed Atef Tawfik,Ashraf Ahmed,Joung-Hu Park 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.8

This paper proposes an effective VAR source established as a cascaded H-bridge (CHB) static compensator (STATCOM), which is based on the flux cancellation method. The conventional CHB-STATCOM uses a low-frequency large capacitor as a source. The required capacitance value of the capacitor increases as a function of the amount of VAR produced to compensate the power system. The proposed topology is based on flux cancellation. Therefore, the source of VAR in this case is not limited by the capacitors or the power decoupling transformer size. The sub-module (SM) of the proposed topology comprises of a CHB module with power decoupling circuits. The double-frequency ripple powers on the sub-module (SM) capacitors, which have a phase shift of 120° with respect to each other. The ripple powers are derived from each of the three phases toward a common magnetic core to cancel each other out. An isolated bidirectional triple port dual half-bridge converter is utilized for the flux cancellation process. In this converter, the main challenges are leakage inductances and the high voltage insulation among the three windings of the high-frequency transformer. An αβ-frame-based model is proposed, using the generalized state-space averaging method, for the flux cancellation circuit. Furthermore, the size is significantly reduced by the proposed method, since a small sub-module capacitance of a few microfarads is sufficient to operate the CHBSTATCOM. The analysis and the controller design process are presented, followed by simulation and hardware validations.

Loss Analysis of Nanocrystalline Cores for High Frequency Transformer in Power Electronics Circuits

Munir Muhammad Umair,Ehab Muhammad,Tawfik Mohamed Atef,Ahmed Ashraf,Park Joung-Hu 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.3

Nanocrystalline cores have a superior higher permeability, which makes them smaller size and weight compared to conventional cores. This makes nanocrystalline more suitable to many applications, such as electrical vehicles, EMI flters, so on. This paper compares power-conversion performance between nanocrystalline and conventional ferrite cores of similar volume. A 1 kW dual-active bridge converter is used for testing the transformers at 50–80 kHz. Theoretical losses are calculated from datasheets and compared with the experimental losses for both the nanocrystalline and ferrite. Results reveal that the theoretical and experimental losses match for ferrite transformer but there exists a signifcant diference in case of the nanocrystalline transformers. Further investigation is needed to explain this mismatch. Therefore, FEM analysis using COMSOL Multiphysics is performed. Due to the nonlinearity of the material, a homogenized anisotropic confguration is adopted. The experimental and FEM results suggest that the mismatch is possibly because of the circulating eddy currents between the ribbons, which must be taken into consideration during the modeling of the losses for nanocrystalline cores.

Integrated Decoupled Inductors for Interleaved Boost Converters

Shamroze Fayyaz(파예즈 샴로즈),Muhammad Umair Munir(무니르 무하마드 우마이르),Mohamed Atef Tawfik(모하메드 아테프 타우픽),Ashraf Ahmed(아쉬라프 아메드),Joung-Hu Park(박종후) 전력전자학회 2023 전력전자학술대회 논문집 Vol.2023 No.12

Single-Ended ISM-Band Frequency DC-DC Converter with Very High Step-Up Voltage Gain

Muhammad Umair Munir(무니르 무하마드 우마이르),Shamroze Fayyaz(파예즈 샴로즈),Mohamed Atef Tawfik(모하메드 아테프 타우픽),Ashraf Ahmed(아쉬라프 아메드),Joung-Hu Park(박종후) 전력전자학회 2023 전력전자학술대회 논문집 Vol.2023 No.12

Performance evaluation of carbon nanotube yarn‑based inductors for ISM‑frequency band soft‑switching converters

Jung-Hwan Park,Kyoung-Tak Kim,Chun-Gu Lee,Mohamed Atef Tawfik,Muhammad Ehab,Muhammad Umair Munir,Ashraf Ahmed,Joung‑Hu Park 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.11

With the advancement of carbon material science, there have been attempts to apply carbon nanotubes in various engineering fields. In power electronics, application research has been conducted on using carbon nanotube (CNT) yarn in inductors, transformers, and motor windings, because CNT yarns show promising mechanical and electrical characteristics when compared with conventional conduction materials. This paper evaluates the feasibility of CNT yarn-based inductor applications with respect to higher-frequency power converter circuits, especially focusing on the ISM (Industry–Science–Medical) frequency range. Inductors are fabricated using two kinds of CNT yarns with different conductivity values. These inductors are compared with copper and lead coiled inductors, since they have a relatively high conductivity with respect to CNT yarns, and due to their popularity in the industry. The small-signal impedance data of each inductor according to the frequency variation are measured using a network analyzer, and the measurements were compared with a COMSOL simulation. One of the main results of this research is that the CNT yarn-based inductors were shown to have a better normalized AC resistance characteristic than the conventional conductor inductors, which have higher conductivity. It was found that CNT inductors have a similar AC resistance when compared to that of metallic conductors with nearly 1.85 times higher conductivity. A 100 W differential class-E resonant converter is implemented to test the inductors and to verify the small-signal measurement results. Efficiencies and thermal images are obtained at 6.78-MHz and 13.56-MHz ISM frequencies.