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Generally, the output power of the Photovoltaic (PV) panels is less than the nominal rating of the panel. On the other hand, the inverters of the PV systems are normally sized smaller than the nominal rating of the photovoltaic system. A typical PV to inverter power rating ratio is 1.2, which can be influenced by the weather condition. The main drawback is that during peak irradiance and optimal temperature situation, the peak power is generated at the PV, but the inverter is not sized for absorbing the whole power. This article develops a systematic method to calculate the optimal ratio between PV panel and inverter to absorb the maximum possible power with an optimal cost. This method uses the annual irradiance and temperature of the geographical region and extracts the power curves for a photovoltaic system in specific regions. Based on the distribution of the various weather conditions, the total possible power generation of the system is calculated. Then the possible extracted and lost power for different sizes of inverters are calculated to develop an efficiency function for the extracted power of the typical power system. This function is optimized considering the price of inverters and system. Both of conventional 1000 V PV system as well as recently developed 1500 V system for 480 VAC grid connection are studied and the effect of transformer in both case is investigated. The paper shows how 1500 V system is superior to its 1000 V counterpart. 

Development of the new generation of high power and high frequency power electronic switches along with the need for compact controllable converters for utilization of distributed energy resources in the grid, have led to significant developments in the area of solid state transformers in the last years. The design process of a high frequency transformer as the main element in the solid state transformer is illustrated in this article. A multi winding transformer for multiport SST application is designed, studied and built in this research. In a MPSST several windings feed the core. As the result, coupling coefficient between each pair of windings, become an important factor which is studied in this study. Since the transformer is designed for high frequency applications, the power loss in the wire and core of the transformer increases as the result of higher skin effect and eddy current loss in high frequency. Three important factors in the design of HF transformer for MPSST are discussed in the paper. First, four different possible core materials are compared based on their flux density, frequency range, loss and price. Then the cable selection is illustrated and finally, different winding placement and distribution on the same core are suggested and the inductance and coupling coefficient matrices are calculated using ANSYS Maxwell 3D simulation. The transformer is built in the lab and the inductance values matches the expected values from the simulation.