• Energy Research
• 2021-2025close
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The present paper exhibits a real time assessment of a robust Energy Management Strategy (EMS) for battery-super capacitor (SC) Hybrid Energy Storage System (HESS). The proposed algorithm, dedicated to an electric vehicular application, is based on a self-gain scheduled controller, which guarantees the H∞ performance for a class of linear parameter varying (LPV) systems. Assuming that the duty cycle of the involved DC-DC converters are considered as the variable parameters, that can be captured in real time, and forwarded to the controller to ensure both; the performance and robustness of the closed-loop system. The subsequent controller is therefore time-varying and it is automatically scheduled according to each parameter variation. This algorithm has been validated through experimental results provided by a tailor-made test bench including both the HESS and the vehicle traction emulation system. The experimental results demonstrate the overall stability of the system, where the proposed LPV supervisor successfully accomplishes a power frequency splitting in an adequate way, respecting the dynamic of the sources. The proposed solution provides significant performances for different speed levels.

In our research we identified 45 business model patterns with the potential to support sustainable business design. These patterns were arranged in groups based on commonalities in the sustainability challenges the patterns address. The following 11 groups will be presented in detail in our forthcoming book:  Group 1: Pricing & Revenue Patterns primarily address the revenue model of a business model, i.e. these patterns define how offerings are priced and revenues generated.  Group 2: Financing Patterns address the financing model within a business model, i.e. these patterns define how equity, debt, and operating capital can be acquired.  Group 3: Eco-Design Patterns integrate ecological aspects into key activities and value propositions, i.e. these patterns define how processes and offerings are designed to improve their ecological performance over their entire life cycle.  Group 4: Closing-the-Loop Patterns help integrate the idea of circular material and energy flows into partnerships, key activities, and customer channels, i.e. these patterns offer alternative ways of how materials and energy flow into, out of, and return to a company.  Group 5: Supply Chain Patterns modify the upstream (partners, resources, capabilities) and/or downstream (customers, relationships, channels) components of a business model, i.e. these patterns define how inputs are sourced and target groups are reached.  Group 6: Giving Patterns help donate products or services to target groups in need, i.e. these patterns define how costs are covered and social target groups are reached.  Group 7: Access Provision Patterns create markets for otherwise neglected target groups, involving modified value propositions, channels, revenue, pricing and cost models, i.e. these patterns define how value propositions are designed, delivered, and to whom.  Group 8: Social Mission Patterns integrate social target groups in need, including otherwise neglected groups, either as customers or productive partners, i.e. these patterns define how customers, partners, and employees are defined and integrated.  Group 9: Service & Performance Patterns emphasize the functional and service value of products and offer performance management, i.e. these patterns are special in how value propositions are defined and delivered.  Group 10: Cooperative Patterns integrate a broad range of stakeholders as co-owners and co-managers, i.e. these patterns are special in how partners are defined and how the organization is governed.  Group 11: Community Platform Patterns substitute resource or product ownership with community-based access to resources and products, i.e. these patterns offer alternatives to how value propositions are defined and delivered.

Abstract The integration of the Photovoltaic (PV) - based Distributed Generation (DG) Systems to the conventional electrical grid is a significant issue to achieve a confidential grid operation. This study presents a novel structure for the suppression of the common-state leakage current for PV-based inverters. It investigates the real-time performance of the inverter for the grid-code compatibility of the PV-based microgrid applications. Many of the topologies have been introduced to suppress leakage currents in grid-based Photovoltaic (PV) inverters, but most of them cannot practically reach more than 95% efficiency. The number of the components, especially the switching semiconductors, including the power switches and power diodes and the current and ripples' level in the topology filter side inductors, are essential criteria for efficiency. The proposed inverter includes six power switches and two power diodes. Since different operational states, only two power components per branch of the inverter are activated a higher efficiency than the conventional H5, H6, and HERIC converters. It presents the THD equal to 1,42 for load-connection states that is considerable. This converter can also generate pure sinusoidal current and voltage waveforms for the reactive loads, especially resistive-inductive load connections that are most common in industrial applications. As a study-case, the implemented inverter was tested under different grid conditions in the laboratory, and a real-time LabVIEW-based monitoring and grid protection system was realized within the research scope. Under/over-frequency protection and under/over voltage protection were performed to provide a reliable microgrid management system for the developed inverter. According to IEEE 929-2000 threshold values for the breakers' reaction operation under the ±10% as the output threshold voltage, the converter's performance is presented. A real-time monitoring and protection system are developed, and the developed LabVIEW analyzer has done the hardware test results. THD and spectrum analysis are also investigated in the real-time domain by the developed inverter test system. In this way, the implemented inverter's grid code compatibility is investigated in real-time, and the experimental results show that the proposed inverter is reliable for PV-based microgrid applications.

Abstract Field experiences have shown that sub-synchronous oscillation (SSO) can occur in direct-drive wind farms with VSC-HVDC systems. Due to the complexity of the detailed wind farm model, a dynamic equivalent model, with a reasonable order reduction of the detailed model and still reflecting inside-wind-farm and wind-farm-grid SSO characteristics is essential. In this paper, based on the principle that similar matrices have identical eigenvalues, the SSO analysis of an N-machine wind farm with VSC-HVDC system is conducted by simplifying it into two single-machine systems. The modeling method of the two single-machine systems is presented. Four case studies are presented to verify the effectiveness of the proposed model when compared with the detailed model in various scenarios. The proposed model is also benchmarked with the output multiplication-based equivalent model (OMM). Comparison results show that although the system order is reduced significantly, the proposed simplified equivalent model can still reflect inside-wind-farm and wind-farm-grid SSO modes in various scenarios. Meanwhile, the rationality of the OMM in terms of the wind-farm-grid SSO analysis is verified theoretically.

Abstract This paper studies optimal shunt busbar capacitor placement for large-scale VSC-MTDC grids to accurately discriminate between faults inside each protection zone and external faults. The installed capacitors work as filters, which attenuate higher frequencies for faults outside the zone and keep internal fault transients unchanged. The objective function is a trade-off between total installation and maintenance cost and the discrimination sufficiency, while constraints related to the grid operation must be satisfied. Discrete wavelet transform (DWT) is used to calculate wavelet energies and to define relay detection criteria. The proposed method is applied to CIGRE large-scale VSC-MTDC grid in PSCAD/EMTDC. MATLAB is used for DWT-based signal processing with Python used as an interface between PSCAD and MATLAB for optimization based on the Watercycle optimization algorithm (WCA). Multiple faults with different characteristics are simulated to test the optimal results in different situations. The optimal results show that the proposed principle accurately discriminates between internal and external faults. Simulation results prove accurate detection of the faulty section using both two-sided measurement and one-sided measurement with half of measuring and protection equipment. The sensitivity of the method to faults close to the measuring points and the impact of different DWT levels is analysed.

Abstract With the large-scale integration of the distribution generations (DGs) and the increasing medium-voltage and low-voltage DC power demands, multi-terminal hybrid AC/DC microgrid has drawn great attention from researchers around the world. In order to reduce the number of power conversion stages and meet DC transmission demands under different DC voltage levels, this paper proposes a four-terminal interconnection scheme of the hybrid AC/DC microgrid, connecting one medium-voltage AC (MVAC) terminal, one medium-voltage DC (MVDC) terminal and two low-voltage DC (LVDC) terminals. The proposed interconnection scheme includes a modular multilevel converter (MMC) as the main interlinking converter of the MVAC grid and MVDC microgrid, and a series of dual active bridges (DAB) converters as two isolated LV DC microgrid interfaces. It has more flexibility for power supplies, especially MVDC transmission, and a more robust tolerance for unequal power distribution between the two LVDC Microgrids. To realize the DC capacitor voltage balancing control, an improved energy control method is proposed in this paper. The proposed method keeps DC capacitor voltage balance and AC current zero on the MVDC transmission lines, which contributes to the stability of the MVDC microgrid. In addition, the symmetry of the AC currents is also guaranteed with this control method. Validation results of a four-terminal hybrid AC/DC microgrid verify the effectiveness of the proposed microgrid and control scheme.

Abstract Hydrothermal liquefaction (HTL) is a promising technology for converting organic-rich waste biomass such as swine manure (SM) and sewage sludge (SS) into energy-dense bio-crude. Until now, one of the major challenges associated with HTL is the pumpability of high dry-matter containing fibrous feedstocks for continuous processing. In this context, this batch scale study presents a suitable approach for enhancing the pumpability of the fibrous material, specifically SM, by co-processing with SS. Obtained results showed that SM was not pumpable itself due to its fibrous nature, but became pumpable by the addition of SS at overall 25 % dry matter content. It was highlighted that the sample mixture containing ~80 % of the SM was smoothly pumped with 20 % SS. Subsequently, HTL experiments were carried out on samples mixed under the ratios SM:SS (100:0, 0:100, 50:50, 80:20, and 20:80). The highest bio-crude yield (42.38 %) via maximum synergistic effect was obtained from the sample SM/SS (50:50) at ratio 1:1 with the best HHV of 36 MJ/kg. Almost 60–70 % mass of all bio-crudes contained volatiles at 350 °C. ICP-AES measurements revealed that the majority of the inorganic elements were concentrated into the solid phase, while 40–50 % of the potassium and sodium were transferred to the aqueous phase. In conclusion, using SS as a co-substrate with SM not only enhances the pumpability of SM, but its co-liquefaction has demonstrated beneficial synergistic effects on improving the energy recovery of the bio-crude.

Abstract With the increasing access of renewable energy resources and fast ubiquitous connection of everything, the traditional one-way power flow from centralized generation to end consumers will give way to bidirectional-way power flow with multidirectional energy network among central grids and distributed prosumers. To empower the prosumer-centric Energy Internet (EI) and enhance the integration of energy-aware services, digitalization and decentralization are the key enablers to achieve transactive EI. This article presents a systematic overview on how Internet of Things (IoT) drives the digitalization of transactive EI and how blockchain empowers the decentralization of transactive EI. A comprehensive discussion on the key infrastructures is provided for presenting how to implement digitalization and decentralization of transactive EI, including the last mile “Advanced metering infrastructure” (AMI), renewables integrator “smart inverter”, energy flow adjuster “energy router”, and coordinator “Microgrid”. Challenges and future trends are discussed from an extensive point of view, including energy physical space, data cyber space and human social space.