Optimized Phase‐shift Tuning via Equivalent Small Parameter Modeling for Ripple Reduction in Asymmetric Parallel Multi‐Module DC‐DC Converters

In parallel converters applications, direct parallel topology was respected because of the advantages of small size, low cost, simple structure and easy to extend. However, the coupling effects maybe exist because the parallel converters are connected by non-isolated mode. In this paper the average model was proposed in the rotating coordinate system. As the entire system is a symmetric structure, the parallel converters with the proposed modulation strategy can reduce common mode dv/dt noise and differential mode current ripple effectively.

Dual active bridge (DAB) converters are widely used in dc microgrids due to their advantages of electrical isolation, wide voltage range operation, and bidirectional power flow. When the voltage conversion ratio is mismatched, the conventional symmetric phase shift modulation method has a narrow zero voltage switching (ZVS) range, low light-load efficiency, and uncontrollable inductor current oscillations caused by abrupt changes in variables during mode switching. In order to solve the above-mentioned problems, an extended dual side asymmetric phase shift modulation (EDAPSM) and smooth mode transition method is proposed in this article. Analytical solutions over the entire power range are derived based on the proposed approximation method. The inherent cause of variable discontinuities during mode transitions is identified, and a novel approach to achieve smooth mode switching is presented, thereby improving the efficiency of the DAB converter over a wide voltage range, particularly under light-load conditions. A 1-kW DAB prototype is constructed, and the modulation method can achieve a maximal efficiency of 98.03%. The experimental results verify the correctness and effectiveness of the method proposed in this article.

Recycling solar panels has been a revolutionary procedure that has affected sustainability practices in the renewable energy industry in the past, present, and future. With silicon photovoltaics contending for market share to reduce solar power costs, perovskite photovoltaics is becoming more popular. However, there is currently no practical means to manage dangerous lead Pb waste, which could spell the end of this technology. We offer a material management method for perovskite solar modules that addresses the end of their useful life. The goal is to recycle valuable transparent conductors and toxic lead to save the environment and promote the economy using recycled materials. An action plan for removing poisonous lead and precious glass substrates from perovskites-based solar panels. Organic solvents, such as dimethylformamide (DMF), dissolve lead in the perovskite layer during delamination of encapsulated perovskite solar panels. To entirely remove lead from organic solvents, an adsorbent adsorbs ions, eluted into a clean solvent for broth enrichment, and the precipitated PbI2 is collected for recycling. In this case, we used carboxylic acid cation exchange resin as an absorber to recycle lead from used perovskite modules. To reuse the used perovskite solar cells, a procedure must first be developed to unbind the encased modules and expose them to the perovskite layer. This section examined the composition of a perovskite module formed of indium tin oxide (ITO) glass and encapsulated by an additional piece of glass. Although silicon solar panels contain a large number of valuable materials, such as silicon, glass, silver, aluminum, etc., they still lack the cost-effective recycling technology that would allow them to be recovered. Silicon is incredibly diverse, but its high-value applications, such as semiconductors, require the same stringent purity requirements. However, employing it as an anode material in lithium batteries with less severe purity standards appears viable.Furthermore, abandoned solar cells have been shown to include silicon anode impurities such as boron, phosphorus, and silver, which improve their stability. There are now two phases in PV recycling: dismantling and filtration. Although silicon PV panels vary greatly, they all share the same basic construction. The sandwich construction solar cells, comprised of aluminium, silicon, and silver, are joined to modules by copper wires soldered with lead and tin (Pb and Sn). The modules are then sandwiched between two EVA layers, creating a waterproof seal.Alternative processes, like pyrolysis and chemical treatments, are used to gently peel off glass and solar cells to recycle Si and Ag by removing or extracting EVA. EVA is commonly used to coat and preserve solar cells and PV panels. This encapsulation makes it more difficult to separate the glass cover and back sheet and recycle the solar cells.Morphology conversion must be considered throughout the upcycling process, which employs nano-metal catalysed hydrofluoric acid (HF) acid etching to recover porous Si/carbon anode materials after a brief purification step. Because of the properties of silicon, HF is always used to form silicon pores, which are not meant to last. As a result, HF can be replaced in purification and morphological modification, resulting in a more environmentally friendly and long-lasting recycling process. The silicon wafer can also be recycled in all-solid-state batteries (ASSBs). This method states that after removing the perovskite and carbon, the metal oxide layers (TiO2, ZrO2) produced on the FTO can be reused to remanufacture enclosed carbon-based perovskite cells. In a solar simulator based on xenon lamps, the power conversion efficiency of perovskite solar cells and solar modules was measured using current-voltage (JV) measurement. Based on the study and comparison of solar PV production and the avoided burden approach due to recycling, it is possible to infer that recycling in the total life cycle evaluation of solar PV can result in a significantly higher impact reduction throughout the solar PV recycling process. Keywords Solar module recycling, Chemical recycling, End-of-life management, Upcycling, Circular economy, Refurbishment.

The primary objective of Maximum Power Point Tracking (MPPT) for PV systems connected to a low-voltage DC grid is to extract the maximum possible power output from the PV array. Normally high-frequency switched mode power converters are employed to track the maximum power. These converters, however, impose switching frequency voltage ripple on the PV output. This causes fluctuation around the Maximum Power Point (MPP) and results in power loss. These losses can be reduced using electrolytic capacitors, however, the electrolytic capacitors’ lifespan is relatively shorter than that of a PV panel. In this paper, an interleaved boost converter is used to reduce high-frequency voltage ripple introduced on panel. Hence, smaller values of longer lifespan capacitors such as film capacitors will be sufficient to curtail the smaller ripple. Moreover, film capacitors are selected based on voltage ripple. Analysis was carried out for calculating voltage ripple imposed on PV module to select input filter more precisely. In addition, reduction in the voltage ripple is calculated quantitatively and is compared with that of a conventional boost converter. Enhanced power output from the PV panel is mathematically proven and experimentally demonstrated.

Bipolar DC microgrids (BDCMGs) have several issues related to the voltage and require numerous converters to supply power to both poles. To solve these issues, a bidirectional dual-input dual-output (DIDO) converter is proposed for the voltage balancer in BDCMG. The DIDO converter has dual-input sources and a dual-output port connected to the grid. Additionally, the DIDO converter simultaneously performs independent bidirectional power control and voltage balancing control. Based on the input voltages, this paper proposes modulation methods for three cases. The modulation method of the second case has a wide operating range and low balancing current ripple without increasing the switching frequency. Moreover, only voltage balancer mode without active input sources is proposed, considering the intermittent source. Therefore, it can operate as a voltage balancer under all conditions. The voltage balancing performance of the three cases was analyzed. Finally, the proposed modulation and control method of the DIDO converter were verified through experimental results.

The independence of reactive current injection from the active power produced by distributed generators makes the inverters a key element in improving grid stability, particularly during grid faults. This paper proposes a new per-phase control strategy for three-phase inverters during asymmetrical and symmetrical grid fault conditions. The control strategy guarantees the safe operation of the inverter during voltage sags. As a result, the grid is better supported since the voltage at the point of common coupling is improved in each phase independently. In particular, this paper introduces a new control strategy to raise the Point of Common Coupling voltage based on the voltage reduction in each phase and to avoid undervoltage during grid fault conditions. Simulation results verify the effectiveness of the proposed method. The simulations are carried through Matlab environment.

This paper proposes an optimized control strategy for any modular multilevel converter (MMC), based on a generalized space vector modulation (SVM) method. By fully utilizing the flexibility of the SVM method, i.e., the redundant switching sequences and adjustable duty cycles, this optimized control strategy enables optimal capacitor-voltage and circulating-current control of the MMC. The proposed control strategy can also be implemented with other pulse width modulation methods, e.g., the carrier-based modulation and the nearest-level modulation, though sophisticated selection of the common-mode voltage injection may be required. This paper therefore also demonstrates that for the MMC, the SVM is more flexible than other modulation methods. Typical case studies are given to validate the analysis.

Within the last years, a new characterization method for solar modules called Magnetic Field Imaging (MFI) has been introduced. MFI reveals the strength as well as the direction of currents flowing within solar modules by analyzing the magnetic field distribution and thereby allows to trace back electrical defects. Within our work, we demonstrate how MFI can be exploited to characterize solar modules that contain stripe-like solar cells interconnected in a roof tile manner - so called shingle solar modules. In comparison to conventional solar modules, shingle modules yield the potential for higher power densities, exhibit a more homogeneous appearance and are less prone to power losses when being partially shaded. Due to these advantages, shingle solar modules are expected to gain a growing share of the solar module market within the next years, reaching 11% by 2027. As we demonstrate, MFI allows to detect different defects that are typical as well as unique for shingle solar modules, namely a local shunt by smudged electrically conductive adhesive (ECA), a systematic tilt between individual shingles, and locally poor shingle interconnection. Each defect type shows a fingerprint-like characteristic within MFI measurements and thus can be identified without ambiguity. Compared to electroluminescence (EL), MFI tends to display the defects more prominent and clearer. Furthermore, we demonstrate that MFI can be used to study the response of shingle modules to partial shading and observe that the module current bypasses shaded regions, as predicted by theory. We conclude that MFI would allow to investigate any kind of module under partial shading revealing the current flow through the solar cells, the connectors, and the bypass diodes.

Converters parallel operation can increase capacity of the system, but it may lead to potential zero-sequence circulating current, so the control of circulating current was an important goal in the design of parallel inverters. In this paper, the Real Time Digital Simulator (RTDS) is used to model the converters parallel system in real time and study the circulating current restraining. The equivalent model of two parallel converters and zero-sequence circulating current(ZSCC) were established and analyzed, then a strategy using variable zero vector control was proposed to suppress the circulating current. For two parallel modular converters, hardware-in-the-loop(HIL) study based on RTDS and practical experiment were implemented, results prove that the proposed control strategy is feasible and effective.

An advanced co-phase traction power substation system based on the cascade- parallel converter was proposed in this paper, for addressing the power capacity problems of traction power substation and the problems of electrification phase, reactive power, negative sequence and harmonic in railway. The 3-level neutral point clamped (NPC) converter was used in power substation, while the converter was cascaded and paralleled to approve the capacity of system. The system can transfer active power directly between power gird and traction network, the power factor of which is 1, and the neutral-section passing device is canceled completely, which is an ideal co-phase traction power supply system. In this paper, current sharing performance of traction network based on this system is analyzed. The impedance performance of traction network and circulating current characteristic of the system are presented in detail. And then the circulating-current restraining strategy is analyzed, the droop control is proved to achieve a system of parallel. The system is proved having droop characteristic and can parallel operate with multiple converters by using drooping control, achieving current sharing. The simulation results verified the theoretical analysis and that the system achieves current sharing. The control strategy and modulation strategy is verified by experiment.

This paper presents a unified carrier-based modulation method for direct matrix converter. Various types of pulse width modulation (PWM) methods are generated by using the offset voltage, changing slope of carrier waveform, and adjusting the free parameters in the modulation algorithm. The proposed method is equivalent to the space vector pulse width modulation (SVPWM) for two-level and three-level voltage source inverter (VSI). This paper also presents a new viewpoint to understand the matrix converter modulation method such as single carrier based modulation technique for two-level VSI and double carrier based modulation technique for three-level VSI. Using the proposed method, this paper presents discontinuous pulse width modulation (DPWM) for the matrix converter. Therefore, a unified simple algorithm suitable for the digital implementation of all continuous and discontinuous PWM strategies is proposed. The feasibility of the proposed modulation method has been verified by a computer simulation results. These results show that the proposed carrier-based modulation method can be implemented easily without any tables.

Comprehensive cell to module optical loss analysis of metal assisted chemically etched inverted pyramid textured multi-crystalline silicon solar cells and modules by ray-tracing method

The free fermionic classification method provides a powerful tool to investigate string vacua, which led to the discovery of spinor--vector duality and exophobic string models. We extend the classification methodology to both $\mathcal{N}=1$ and $\mathcal{N}=0$ Flipped $SU(5)$ $\mathbb{Z}_2 \times \mathbb{Z}_2$ heterotic string orbifolds with asymmetric shifts. The impact of the asymmetric assignments on the phenomenological characteristics of these models is investigated. Of particular interest is the analysis of untwisted moduli fixing for various choices of asymmetric boundary conditions. Two classes of vacua with different characteristics are systematically investigated with help from SAT/SMT algorithms, which are shown to increase search efficiency by up to two orders of magnitude, as well as providing useful tools to find contradictions between various phenomenological criteria. The general form of the partition function for the space of models is explained and given for two specific example models for different choices of asymmetric boundary conditions. Additionally, the distribution of one-loop cosmological constant contributions for samples in the two different classes of models are depicted and discussed.

This paper proposes a transient modeling and analysis method for the fractional-order DC-DC converters in continuous conduction mode (CCM), in which a fractional-order Buck converter is taken as an example. By extending the usage of equivalent small parameter method (ESP), the converter is modeled by a general state vector differential equation. Then by adopting the principle of harmonic balance, fractional differential of state variables is converted into linear operations of exponential functions, and different harmonic are separated. Thus the main transient oscillation components of state variables can be obtained according to Grunwald-Letnikov's definition of fractional derivation, and the data are processed approximately by polynomial fitting of triangular functions. The results are introduced back to the model to obtain the values of the rest harmonic magnitudes. So the final solution of state variables is in the form of the summation of harmonic contents. To confirm the correctness of the results of the proposed method, waveforms of the analytical solution are put together with those from circuit simulation in PSIM. These results demonstrate the high effectiveness of the proposed method.

Comprehensive analysis and modeling of cell to module (CTM) conversion loss during c-Si Solar Photovoltaic (SPV) module manufacturing