Centralized inverter technology is one of the most common architectures of the PV installation, which interfaces a large number of PV panels that configured in series-parallel (SP) combination to the ...grid. However, the power generated from centralized inverter architecture based on SP array topology is significantly reduced under the non-uniform aging condition. Non-uniform aging of PV panels is a common problem in the PV generation plants, as they often operate under harsh outdoor environmental conditions for a long service period. Due to the elevated price of replacing aged PV panels with new ones, it is preferable to improve the power extracted from aged PV systems. This paper proposes a circuit-based topology known as current collector optimizer (CCO) topology to enhance the performance of centralized inverter technology under the uneven aging condition of PV modules. According to the results, the maximum power extracted from the non-uniform aging PV array is substantially increased by using the CCO topology compared to the conventional SP array topology with bypass diodes. With CCOs, the PV array characteristics have a unique maximum power point (MPP) which can be easily followed by a simple MPP tracking algorithm, subsequently, the CCO topology does not suffer from misleading power losses. The proposed topology requires offline rearrangement of aged modules to obtain the optimum power if only the degradation rate of short-circuit current is used to assess the aging process. Furthermore, the CCO topology operates close to optimum power if the degradation rate of open-circuit voltage is taken into account.
•CCO topology is used to enhance energy harvest from non-uniform aging PV modules.•CCO topology does not suffer from misleading power losses.•Optimum power is obtained if SC current is used to assess the aging process.•Close to optimum power is achieved when SC current and OC voltage are used to evaluate the aging process.
•Analytical efficiency model considering power losses in meshing and bearings.•Convergence of the results obtained by calculations and by testing the prototype.•High efficiency of the transmission at ...nominal load (90–96%).•Power loses in rolling bearings are several times greater than in meshing.
The aim of the article is to investigate the efficiency of the novel eccentric rolling transmission, which is a simplification of the cycloidal reducer, with parallel but not overlapping shaft axes. In this paper, a kinematic and load distribution analysis are presented with a view to determining the forces and rotational speeds necessary for efficiency calculation. The developed efficiency model involved power losses in rolling bearings, at meshing, as well as churning and windage power losses. For the verification, a transmission prototype with a 10:1 gear ratio and a dedicated test stand were designed and built. The results of the research showed that most substantial power losses occurred in the bearings and were several times greater than the losses associated with friction between the active surfaces of its main components. The transmission efficiency improved with increasing load and decreased with increasing rotational speed, reaching a maximum of 96% at nominal torque. The proposed model allows predicting the efficiency of the transmission at the stage of its design, which can further facilitate the optimization of the transmission parameters considering expected operational conditions.
In 2021, the world's total installed capacity of generation units based on renewable energy sources (not including hydropower) amounted to about 1674 GW: over 825 GW and 849 GW of wind and solar ...power plants were installed respectively. The growing of the installed capacity of these distributed generators is a response to the increasing the power consumption, global environmental issues and has also become possible due to the development of technology in field of power semiconductor devices. However, on the way of large-scale implementation of distributed generators based on renewable energy sources, traditional electric power system meets new challenges to ensure the reliability and sustainability of new electric power systems with renewable energy sources. In particular, distributed generators change processes in the electric power system, impact to the parameters and power balance, change the magnitude and direction of power flow and short-circuit current, which determines the need to update the settings of the relay protection and automation systems of traditional electric power system and to coordinate their operation with automatic control systems of installed distributed generators. The above-mentioned tasks form a number of scientific research directions, one of which is a task of determining optimal size and location of distributed generators. The main purpose of this optimization task is to reduce power losses, operating and total electricity cost, improve the voltage profile, etc. In addition, the correct and reasonable placement of distributed generators defines an effective planning of the operating modes of electric power system and power plants (especially based on renewable energy sources, the operating modes of which depend on weather conditions and can be sharply variable).
The paper highlighted the impacts of distributed generators on power losses, the voltage level, maintaining the power balance and the possibility of participating in the frequency regulation, and short-circuit current in power system. The optimization criteria, the main limiting conditions, as well as methods for solving this optimization problem are considered. This review will help the System operators and investing companies, especially in Russia, to form the main aim, objective function and constraints that will aid to meet their load demand at minimum cost and to choose from the options available for optimization of location and capacity of distributed generators.
Дослужено OKnadoei втрат активно'! потужностi в дальних електропередачах змтного струму. Показано, що в режимах малих та середшх навантажень основну частку втрат складають втрати на корону. ...Недосконалтть чинно! методики визначення втрат потужностi на корону, як носять клшатичний характер, обумовлюе споаб виокремлення цих втрат 3İ складу сумарних тсля розрахунку навантажувальних втрат потужностi. Одержано чотирикомпонентну формулу для визначення навантажувальних втрат активно! потужностi. Показано, що задля уточнения розрахунково! моделi необхiдно враховувати фактичну температуру проводу з урахуванням змти погодних умов вздовж траси лти. Наведено результати розрахунку складових втрат активно! потужностi в повтрятй лти 750 кВ «Зах^ноукратська-Втницька» протягом доби 13 вересня 2021 р. БШл. 9, рис. 4, табл. 3.
Fault current limiters (FCL) have high impedance during fault condition. However, it is inevitable to introduce additional impedance to the system, which may increase power losses, cause overvoltage, ...and degrade system dynamic performance. A voltage-clamping type dc fault current limiter (VC-FCL) with low power losses is proposed in this paper. This topology has nearly no on-state loss. Under the demagnetization effect of the coupled inductor, this topology presents very small inductance during normal operation, which is beneficial to the dynamic response of the system. Therefore, VC-FCL can be installed directly into the system without replacing the dc reactor. In addition, the number of power electronic devices and costs are reduced by using metal oxide varistor (MOV) for voltageclamping. The parameter design of the coupled inductor and MOV are carried out to ensure both the current limiting capability and low power losses of VC-FCL. The simulation case study and experiment test are implemented to further verify the good performance of the proposed topology.
Power system automation is an effective tool from both economical and technical aspects to improve the optimal operation of power generators. In this regard, Security Constrained Unit Commitment ...(SCUC) incorporating Dynamic Thermal Line Rating (DTLR) of overhead transmission lines can boost the system security effectively. Using Transmission Switching (TS) tool in SCUC problems leads to cost reduction. Still, one of the main challenges arisen in TS problems is the excessive number of switching in lines, which decreases the lifespan of power switches. In this paper, an Improved Linear AC Optimal Power Flow (ILACOPF) is proposed by using TS and considering Heat Balance Equation (HBE) as a security constraint. Merging dynamic thermal line rating (considering the weather conditions) in SCUC with TS, besides decreasing the number of switching and increasing the lifespan of power switches, causes a remarkable reduction in operating costs. In this power flow, system losses are modeled by linear formulations. Moreover, a linear approximation of the heat losses due to power flow through lines is proposed. To solve the proposed model, Benders' decomposition approach is applied. The performance of the proposed framework has been evaluated on 6-bus and 118-bus IEEE test systems.
Accurate, efficient, and reliable measurements of solar photovoltaic (PV) modules are essential for the evaluation and diagnosis of the actual operating status of PV plants. However, current online ...measurements and extraction models are limited because they do not account for power losses caused by inhomogeneous thermal performance of photovoltaic modules. Accordingly, this paper develops a coupled thermo–electrical loss model to access the power generation, energy losses, and degradation rate of photovoltaic modules with inhomogeneous temperature under actual operating conditions. The experiments indicate that the temperature coefficient of power dissipation and efficiency for solar cells with uneven temperature distribution PV modules are within −0.68W/oC to −0.83 W/°C and −0.46%/oC to −5.81%/oC, respectively. Additionally, the relative error values for the maximum power range from −2.54% to 4.09%, demonstrating the feasibility of the proposed model for predicting the power output behavior of operating PV modules with inhomogeneous temperature distributions. Furthermore, the daily performances of the modules indicate heat and electricity losses ranging from 0.245 kWh to 0.337 kWh, while the ratios of electrical energy dissipation to daily losses vary from 36% to 50%. To ensure the reliability of measuring degradation rates, the solar irradiance thresholds of PV module performance tests are nearly 632W/m2, 781W/m2, 875W/m2, and 875W/m2, respectively. Finally, for the long-term performance valuation, the levelized costs of electricity increase by approximately 0.011 CNY/kWh for every 5% reduction in annual power generation, and the PBP is extended by 4.81yr, 4.22yr, 3.62yr, and 7.10yr, respectively.
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•The thermo–electrical model is developed to access power losses of a PV module.•The temperature coefficient of efficiency is within −0.46%/oC to −5.81%/oC.•The relative error of maximum power for the modules ranges from −2.54% to 4.09%.•The ratios of electrical energy dissipation to daily losses vary from 36% to 50%.•Levelized costs of electricity increase by 0.011 CNY/kWh for every 5% reduction.
•The efficiency calculation uses an enhanced Load Contact Model, which allows for obtaining the Load sharing and the Friction coefficient with a high level of accuracy.•The use of an advanced ...friction coefficient formulation, which can reproduce the friction behaviour in dry contact conditions, boundary, mixed and fluid film lubrication and is dependent of the contact force.•The level of torque and the profile modification effects are taken into account in the Load sharing and Friction coefficient calculation.
In this proposal, the effect of the friction coefficient on the efficiency of spur gears with tip reliefs was analysed. For this purpose, the efficiency values using an average friction coefficient along the mesh cycle were compared with those obtained implementing an enhanced friction coefficient formulation, which is based on elastohydrodynamic lubrication fundamentals. In this manner, it can be established the differences between both formulations in the efficiency and friction coefficient values, as well as the advantages of using this enhanced friction coefficient with respect to formulations implemented in traditional approaches of efficiency calculation. In addition to studying the impact of the friction coefficient choice on efficiency, the profile modifications influence on the friction coefficient and efficiency was also assessed. In this regard, three tip relief case studies were set out; pinion tip reliefs, driven wheel tip reliefs and profile modifications in both gears. From the results, it was inferred that the choice of friction coefficient formulation clearly influences the efficiency in gear transmissions with tip reliefs, obtaining discrepancies between both formulations with regard to which tip relief case study provides the lowest efficiency values.
This paper presents a hybrid modular multilevel converter (MMC), which combines full-bridge submodules (FBSM) and half-bridge submodules (HBSM). Compared with the FBSM-based MMC, the proposed ...topology has the same dc fault blocking capability but uses fewer power devices hence has lower power losses. To increase power transmission capability of the proposed hybrid MMC, negative voltage states of the FBSMs are adopted to extend the output voltage range. The optimal ratio of FBSMs and HBSMs, and the number of FBSMs generating a negative voltage state are calculated to ensure successful dc fault blocking and capacitor voltage balancing. Equivalent circuits of each arm consisting of two individual voltage sources are proposed and two-stage selecting and sorting algorithms for ensuring capacitor voltage balancing are developed. Comparative studies for different circuit configurations show excellent performance balance for the proposed hybrid MMC, when considering dc fault blocking capability, power losses, and device utilization. Experimental results during normal operation and dc fault conditions demonstrate feasibility and validity the proposed hybrid MMC.
This article reviews the design and evaluation of different DC-DC converter topologies for Battery Electric Vehicles (BEVs) and Plug-in Hybrid Electric Vehicles (PHEVs). The design and evaluation of ...these converter topologies are presented, analyzed and compared in terms of output power, component count, switching frequency, electromagnetic interference (EMI), losses, effectiveness, reliability and cost. This paper also evaluates the architecture, merits and demerits of converter topologies (AC-DC and DC-DC) for Fast Charging Stations (FCHARs). On the basis of this analysis, it has found that the Multidevice Interleaved DC-DC Bidirectional Converter (MDIBC) is the most suitable topology for high-power BEVs and PHEVs (> 10kW), thanks to its low input current ripples, low output voltage ripples, low electromagnetic interference, bidirectionality, high efficiency and high reliability. In contrast, for low-power electric vehicles (<10 kW), it is tough to recommend a single candidate that is the best in all possible aspects. However, the Sinusoidal Amplitude Converter, the Z-Source DC-DC converter and the boost DC-DC converter with resonant circuit are more suitable for low-power BEVs and PHEVs because of their soft switching, noise-free operation, low switching loss and high efficiency. Finally, this paper explores the opportunity of using wide band gap semiconductors (WBGSs) in DC-DC converters for BEVs, PHEVs and converters for FCHARs. Specifically, the future roadmap of research for WBGSs, modeling of emerging topologies and design techniques of the control system for BEV and PHEV powertrains are also presented in detail, which will certainly help researchers and solution engineers of automotive industries to select the suitable converter topology to achieve the growth of projected power density.
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