This study presents a new topology of switched-capacitor (SC) multilevel inverter, which is able to step-up input DC voltage to a multilevel AC waveform. This single source inverter is designed based on series connection of the capacitors that charged by input DC sources through a SC network. The proposed modular inverter uses famous T and cross-connected modules that can be simply extended to higher output voltages without increasing the amount of total standing voltage and peak inverse voltage of switches. It generates positive and negative voltage levels inherently, which eliminates requirements of Hbridge inverters that are traditionally used to achieve a bipolar output voltage. Analysis shows that the voltage stress on components, cost, efficiency and losses are kept in acceptable range especially for higher-voltage levels. Capacitor's voltage self-balancing is another inherent advantage of this modular topology which leads to simplify control strategy and eliminate excess balancing circuit. Performance of a six-step proposed structure is evaluated by theoretical analysis, simulation and experimental results.

Abstract-This paper presents a hybrid SHM-SHE switching technique based on pulse amplitude modulation (PAM) concept. It has been applied on a 4-leg NPC inverter to eliminate and mitigate more harmonic orders than recently proposed hybrid SHM-SHE-PWM method while generating switching pulses at the same frequency. In conventional SHE and SHM techniques, equations are solved to attain the switching angles. Regarding the PAM, value of inverter DC voltage can be considered as an additional degree of freedom by which the flexibility of such techniques would be increased maintaining the switching frequency. In the proposed SHM-SHE-PAM, the conventional equations are reformulated to obtain constant switching angles for a vast range of modulation index (m a ) applied on a 4-leg NPC inverter. Switching pulses of the 3 phase legs and the 4 th leg are calculated to mitigate the non-triplen harmonics and eliminate the triplen ones, respectively. Due to the unique switching angles valid in the whole range for m a , the calculation time and volume (storage capacity) are significantly reduced leading to a simpler controller implementable on a low risk and cheap AVR Chip. Experimental tests results of a 4-leg NPC inverter as UPS application prove the good dynamic performance and accuracy of the proposed implemented switching technique in producing associated pulses for the inverter switches at very low frequency to mitigate/eliminate undesired harmonic orders from the output phase/line voltage waveforms without using bulky filters.

In this paper, a novel methodology of PV modeling is proposed to represent the instantaneous electrical characteristics of PV modules covered with snow. The attenuation of the transmitted solar radiation penetrating a layer of snow is rigorously estimated based on the Giddings and LaChapelle theory. This theory introduced the level of radiation that reaches the surface of PV module through snowpack, significantly affected by the snow properties and thickness. The proposed modeling approach is based on the single-diode-five-parameter equivalent circuit model. The parameters of the model are updated through instantaneous measurements of voltage and current that are optimized by the particle swarm optimization algorithm. The proposed approach for modeling snow-covered PV modules was successfully validated in outdoor tests using three different types of PV module technologies typically used in North America's PV farms under different cold weather conditions. In addition, the validity of the proposed model was investigated using real data obtained from the SCADA system of a 12-MW grid-connected PV farm. The proposed model can help improving PV performance under snow conditions and can be considered a powerful tool for the design and selection of PV modules subjected to snow accretion.

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In this paper, a novel universal multi-zone approach of photovoltaic (PV) modeling is proposed to determine the electrical characteristics of PV modules covered with nonuniform snow patterns under partial shading conditions. A precise estimation of the penetrating light into the snow layer on the surface of PV modules is obtained through the theory of Giddings and LaChapelle based on the physical and optical properties of the accreted snow. The single-diode-five-parameter equivalent circuit model of the PV unit is considered as the platform for the modeling approach. Original contributions are brought through: (1) the use of a contour-based discretization methodology that can separate any nonlinear PV characteristics to the multiple linear ones; (2) a swarm-based optimization methodology that is adapted to instantaneously update and evaluate the output characteristics of PV modules and (3) a power loss equation to represent the performance of non-uniformly-covered snowy PV panels. The proposed model was successfully tested using three different commercial types of PV technologies commonly used in North America. The accuracy of the proposed modeling approach for power loss determination was validated by processing real data of a 12-MW grid-connected PV farm. Due to the high extent of snow impact on the PV losses, the proposed model of PV modules could be regarded as a basis not only for analyzing PV plant performance, but also for optimizing the power converter design.

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