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Abstract: This paper proposes a method to evaluate and optimize inverter configurations for grid-connected PV systems. It is studied by Monte-Carlo analysis that how the inverter configuration and its operation strategy would impact on lifetime energy yield and the levelized cost of energy (LCOE) considering the PV array scale, environmental conditions, system cost, inverter efficiency and reliability. The efficiency characteristic of parallel inverters with a common DC bus is deliberated along with the optimal operation strategy. Inverter system performance ratio (ISPR) is proposed as an overall index of lifetime energy conversion efficiency. A case study is performed to demonstrate the proposed method. It shows that the configuration with a common DC bus is a potential solution to reduce the energy cost of PV power generation systems. As ancillary results, it is found that optimizing the PV panel orientation can improve the probability distribution of solar irradiance on the panel, and it is confirmed that an oversized PV array may help reduce the energy cost. [Copyright &y& Elsevier]

In many practical applications of wireless power transfer, the battery, which can be modeled as a voltage source, is charged wirelessly from the voltage-source inverter via the transmitter and the receiver. Therefore, it is crucial to analyze such a wireless power transfer system. In this paper, the closed-form oriented modeling and analysis of the wireless power transfer system with the constant-voltage source and load are conducted. Two cases are studied: both the transmitter and the receiver are under resonance, and only the receiver is under resonance. In the latter case, the transmitter is set to be inductive for the implementation of zero voltage switching. The battery current, the output power, and the transfer efficiency of both cases are analyzed and compared in detail. The voltage gain, the power factor, and the output power of the latter case are studied to offer physical insights and design guidelines. An experimental prototype is implemented to verify the analysis. The experiments agree with the calculations. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient power flow sharing and voltage regulation control method based on hierarchical control to minimize the transmission loss of dc microgrids. Different from the conventional optimal power flow algorithm for the dc grids, the proposed approach needs neither prior knowledge of the grid's conductance matrix nor the load distribution matrix, which means improvement of the expansibility and reduction of the cost. At the primary control level, a voltage droop characteristic is set for each converter to improve the stability and reliability of the grid. The secondary control level aims to regulate the power flow of the microgrid to the optimal condition. The two control levels exchange information by low bandwidth communication. The validity of the proposed approach is verified by both simulation results of a dc microgrid based on IEEE 14-bus system and experimental results on a 50-V two-terminal prototype dc microgrid. [ABSTRACT FROM AUTHOR]

The load coils are employed for multiple loads of resonant wireless power transfer in this paper. With the addition of the load coil, this three-coil structure has easy access to transferring power to multiple loads with the advantages of a compact structure and controllable power flow. Both single-load transfer and multiple-load transfer are modeled and analyzed by means of the circuit theory. The transfer quality factor and the load matching factor are utilized in the analysis of efficiency. In the single-load transfer, the load matching condition is fully explored. Based on the single-load transfer, the multiple-load transfer is researched. The double-load transfer, acting as an illustration, is studied with the uncoupled and coupled load coils. Equivalent reflected resistances are introduced to decouple the model of the double-load transfer with coupled load coils mathematically. An experimental prototype is implemented to verify the aforementioned analysis. The experimental results agree with the theoretical calculations. [ABSTRACT FROM AUTHOR]

In multiple receivers of resonant wireless power transfer, selective power flow among the loads is an important issue. This paper proposes a new method to control power division. The two-coil structure with different resonant frequencies of the sending and receiving loops is modeled and analyzed. The efficiency is proved to peak at the resonant frequency of the receiving loop, regardless of the resonant frequency of the sending loop. Using this feature, selective power transfer can be achieved by setting the receiving loops at different resonant frequencies. The efficiency of a particular load is greatly influenced by the driving frequency. The multiple-load system with different resonant frequencies is modeled and the efficiency expression of each load is deduced. The mutual inductances of the receiving coils have a small impact on the efficiency distribution. The closer the resonant frequencies of the receiving loops, the less isolated the related loads. The calculations and the experiments confirm the analysis. [ABSTRACT FROM AUTHOR]

The nonlinear junction capacitances of power devices are critical for the switching transient, which should be fully considered in the modeling and transient analysis, especially for high-frequency applications. The silicon carbide (SiC) MOSFET combined with SiC Schottky Barrier Diode (SBD) is recognized as the proposed choice for high-power and high-frequency converters. However, in the existing SiC MOSFET models only the nonlinearity of gate-drain capacitance is considered meticulously, but the drain–source capacitance, which affects the switching commutation process significantly, is generally regarded as constant. In addition, the nonlinearity of diode junction capacitance is neglected in some simplified analysis. Experiments show that without full consideration of nonlinear junction capacitances, some significant deviations between simulated and measured results will emerge in the switching waveforms. In this paper, the nonlinear characteristics of drain–source capacitance in SiC MOSFET are studied in detail, and the simplified modeling methods for engineering applications are presented. On this basis, the SiC MOSFET model is improved and the simulation results with improved model correspond with the measured results much better than before, which verify the analysis and modeling. [ABSTRACT FROM AUTHOR]

Although the maximum collector–emitter voltage of a high-voltage insulated-gate bipolar transistor (HV-IGBT) reaches 3300 V or higher, it still cannot satisfy the requirements of some high-voltage high-power converters. Applying power semiconductor devices in series connection can effectively improve the voltage rating and power rating of a power electronic converter. The key issue of device series connection is voltage balancing in static switching state and dynamic switching state. In this paper, a three-level converter based on series-connected HV-IGBTs is presented, its voltage-balancing subcircuits are analyzed, and the parameter design method for the converter is proposed. During the design process, key performance indexes of the series connection circuit, such as the voltage-balancing effect, loss of the voltage-balancing circuit, switching loss, and switching time, are comprehensively considered. Moreover, component parameters of the three-level converter are calculated considering the influence of the voltage-balancing circuit. The proposed parameter design method is applied in the development of a three-level HV-IGBT (4500 V/600 A) series connection test platform with 10 000-V rated dc-link voltage. Experimental results verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]