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This article proposes a three-stage dead-time adjustment scheme for the leading-leg and lagging-leg switches of phase-shift full-bridge converter (PSFBC) according to the load conditions to enhance the conversion efficiencies at light loads. This article also investigates an iterative rigorous loss calculation for light loads under dead-time adjustment. The proposed iterative calculation can be used to modify the duty ratio of the transition region and estimate the operating currents more accurately; therefore, the losses of a PSFBC at light loads and under the dead-time adjustments can be effectively estimated. A PSFBC prototype with an input voltage of 380 V, an output voltage of 48 V, and a rated output power of 480 W is designed and implemented in this article. Experimental results show that comparing with the PSFBC without the dead-time adjustment and with the conventional dead-time adjustment, the conversion efficiency enhancements of 12.13% and 5.97% can be achieved by the proposed three-stage dead-time adjustment scheme at about 5% load condition, respectively. For a small-scale data center with 100 designed PSFBCs, simulated results indicate that about 3.21 MWh of electricity and 1.03 tons of carbon dioxide emission can be saved and reduced per year, respectively, by the proposed dead-time adjustment scheme. [ABSTRACT FROM AUTHOR]

Electric load analysis is an important task in early new stage for design of shipboard power systems (SPSs). The installation generation capacity onboard depends on the accurate result of the analysis, which significantly affects the system economic and secure operations. In the traditional electrical load analysis, the demand factor is often obtained from engineering experiences which may lead to inaccurate analysis results. In order to obtain better results, a methodology for electrical load analysis in SPSs is proposed in this article. The load analysis spreadsheet is adopted to find the power consumption of key electric loads in SPSs. The actual power consumptions of selected loads are collected by intelligent meters. The statistical analysis is then performed to find the critical parameter of each selected load in the load analysis under different operating conditions based on the power measurement of field test and load analysis is performed for estimating system power demand accordingly. The large practical maritime vessel power systems are selected for numerical analysis to ensure the performance of the proposed method. The proposed method has been adopted by local ship builders in Taiwan to better understand the load characteristics in shipboard power systems to support various functions of system planning and operation in a more effective manner. [ABSTRACT FROM AUTHOR]

A fully decentralized controlled (FDC) electric vehicle (EV) charger, where its design is intended to mitigate the charging impact on power grids, is proposed in this paper. The proposed FDC EV charger uses the parameters measured from the power grid, EV charger and EV battery pack to adjust the charging current. Fuzzy logic control is used in this paper to integrate these measured parameters into the proposed FDC EV charger. As the proposed charger can be realized without a centralized control center and information exchanges between EV chargers, an FDC scheme for EV charger can therefore be effectively achieved. A prototype of the proposed FDC EV charger with a rated power of 500 W is implemented. Experimental results verify that the proposed charger can automatically adjust the charging current according to variations in the power grid and EV. Simulations analyze the impact of 100 EVs with a rated power of 7 kW charged simultaneously. Simulation results show that the EV charging impact on power grids can be effectively mitigated by the proposed FDC EV chargers. [ABSTRACT FROM PUBLISHER]

In order to solve the problems caused by the pulsating current ripple of switching-mode power converters, a passive pulsating ripple canceling circuit (PPRCC) is proposed in this paper. The features of the proposed PPRCC include simple, modular structure, and high degree of design flexibility. By integrating the proposed PPRCC, an input current ripple-free flyback-type converter is adopted and analyzed as an example because of its comprehensive utilization in small power rating commercial products. In addition, the switch voltage spike of flyback converter can be suppressed by integrating the proposed PPRCC without using snubbers, it turns out that the efficiency can be further improved. The corresponding operating principle, steady-state analysis, and zero ripple design criteria of the proposed PPRCC are provided. Finally, a 100 W laboratory prototype is constructed to verify the effectiveness of the proposed principle. Experimental results show that the resulting peak-to-peak input current ripple is reduced by 96% and nearly 0.5% and 1.7% improvement in efficiency can be achieved by the proposed PPRCC, at 80 W and 100 W load conditions, respectively. [ABSTRACT FROM PUBLISHER]

The limited capacity of a single inverter has encouraged the usage of parallel inverters for the interconnection of renewable energy generation system. The current-sharing control is one of the commonly used operating strategies for parallel inverters; however, the conversion efficiency using conventional current sharing is low at light loads. Therefore, a smart control strategy for conversion efficiency enhancement of parallel inverters is proposed in this paper. The proposed control strategy is based on the conversion efficiency curve of a single inverter, where a particle swarm optimization based algorithm is utilized to find the optimal conversion efficiency of parallel inverters. Integration of the proposed control strategy into a photovoltaic generation system (PVGS) with a rated output power of 20 kW interconnected by ten inverters with rated output powers of 2 kW is simulated in this paper. Simulation results demonstrate that the proposed smart control strategy can effectively enhance the conversion efficiency of parallel inverters at light loads and increase the electrical energy output of PVGSs. A fully digitally controlled single-phase inverter with a rated output voltage of 220 V and a rated output power of 2 kW is also implemented in this paper. Two implemented inverters are used to validate the performance of the proposed smart control strategy for parallel inverters. Experimental results show that the proposed control strategy can enhance the conversion efficiency of parallel inverters at light loads. [ABSTRACT FROM AUTHOR]

The output power of photovoltaic generation (PVG) varies with solar irradiance and temperature nonlinearly. Therefore, the maximum power point tracking (MPPT) is very important to operate PVG to harvest the maximum solar energy in real time. The perturbation and observation (P&O) method is one of the most commonly used MPPT methods. However, P&O MPPT suffers a tradeoff in selecting the perturbation step sizes of the control variables. This paper proposes a parameter-estimation-based MPPT for PVG. Based on the measured voltages and currents and the characteristic output function of PVG, the proposed MPPT uses parameter estimation to calculate the solar irradiance and temperature directly. The operating voltage of maximum power point can then be found out immediately. The proposed MPPT can effectively reduce the maximum power tracking time of conventional MPPT methods and increase the harvested energy during MPPT. Simulation and experimental results comparing the proposed MPPT to a P&O MPPT demonstrate the performance achieved by the proposed MPPT. [ABSTRACT FROM PUBLISHER]

Fault indicating devices such as fault indicators (FIs) have been widely used in distribution systems to improve reliability and reduce outage duration. Recently, FIs with communication interfaces are integrated into distribution automation (DA) to further reduce fault-finding time by reporting FIs' statuses back to control center. When faults occur, a lot of alarms and fault information are received from Outage Management System (OMS), Trouble Call System (TCS) and Customer Information System (CIS) and are shown to system operators. As a result, the identification of faulted line sections in a wide-ranging distribution system from FIs' statuses is not an easy task, especially when multiple faults occur simultaneously and/or distributed generators (DGs) are connected. An automatic and fast faulted line-section location method for distribution systems based on FIs is proposed in this paper. The line sections between adjacent FIs can be treated as a possible fault location (PFL) and the fault current detected by the FI can be considered as line current (LC) flowing between the adjacent PFLs. A relationship matrix between PFLs and LCs is then derived and used to design the proposed automatic and fast faulted line-section location method. The faulted line sections can then be located effectively and efficiently by the proposed method. Test results for an actual distribution system demonstrate the validity of the proposed faulted line-section location method. [ABSTRACT FROM PUBLISHER]

This paper considers the use of phasor angle measurements provided by phasor measurement units to identify multiple power line outages. The problem of power line outage identification has traditionally been formulated as a combinatorial optimization problem, the optimal solution of which can be found through an exhaustive search. However, the size of the search space grows exponentially with the number of outages and may thus pose a potential problem for the practical implementation of an exhaustive search, especially when multiple power line outages are considered in a power system. To reduce the complexity while improving outage detection performance, we propose a novel global stochastic optimization technique based on cross-entropy optimization, which has been proven to be a powerful tool for many combinatorial optimization problems, to identify multiple line outages. To validate the effectiveness of the proposed approach, the algorithm is tested using IEEE 118- and 300-bus systems, as well as a Polish 2736-bus system. Simulation results demonstrate that the percentage of correctly identified line outages achieved by the proposed method outperforms those obtained by existing sparse signal recovery algorithms. [ABSTRACT FROM PUBLISHER]

Utilizing battery storage systems (BSSs) can reduce the intermittent output of PV generation systems (PVGSs) and make them dispatchable. The aim of this paper is to design an optimal charging/discharging scheduling for BSSs such that the line loss of distribution systems interconnected with sizeable PVGSs can be minimized. A mathematical model for BSSs which can be used to simulate the charging procedures such as the commonly-used constant current to constant voltage (CC-CV) charging method, the discharging procedures and the state of charge (SOC) is proposed first. The minimum line loss problem considering the intermittent output of PVGSs and the scheduling of BSSs is then formulated based on the BSS mathematical model. The optimal charging/discharging scheduling of BSSs can then be obtained by a genetic algorithm (GA) based method. Test results demonstrate the validity of the proposed mathematical model and optimal charging/discharging scheduling for BSSs. [ABSTRACT FROM PUBLISHER]

This paper uses a charging selection concept for plug-in electric vehicles (PEVs) to maximize user convenience levels while meeting predefined circuit-level demand limits. The optimal PEV-charging selection problem requires an exhaustive search for all possible combinations of PEVs in a power system, which cannot be solved for the practical number of PEVs. Inspired by the efficiency of the convex relaxation optimization tool in finding close-to-optimal results in huge search spaces, this paper proposes the application of the convex relaxation optimization method to solve the PEV-charging selection problem. Compared with the results of the uncontrolled case, the simulated results indicate that the proposed PEV-charging selection algorithm only slightly reduces user convenience levels, but significantly mitigates the impact of the PEV-charging on the power system. We also develop a distributed optimization algorithm to solve the PEV-charging selection problem in a decentralized manner, i.e., the binary charging decisions (charged or not charged) are made locally by each vehicle. Using the proposed distributed optimization algorithm, each vehicle is only required to report its power demand rather than report several of its private user state information, mitigating the security problems inherent in such problem. The proposed decentralized algorithm only requires low-speed communication capability, making it suitable for real-time implementation. [ABSTRACT FROM PUBLISHER]

A direct approach for unbalanced three-phase distribution load flow solutions is proposed in this paper. The special topological characteristics of distribution networks have been fully utilized to make the direct solution possible. Two developed matrices—the bus-injection to branch-current matrix and the branch-current to bus-voltage matrix— and a simple matrix multiplication are used to obtain load flow solutions. Due to the distinctive solution techniques of the proposed method, the time-consuming LU decomposition and forward/backward substitution of the Jacobian matrix or Y admittance matrix required in the traditional load flow methods are no longer necessary. Therefore, the proposed method is robust and time-efficient. Test results demonstrate the validity of the proposed method. The proposed method shows great potential to be used in distribution automation applications. [ABSTRACT FROM AUTHOR]