An iterative method for calculating the optimum size of inverter in grid connected PV Systems

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Taweel, Abdulrahman
Bader, Adnan
Milhim, Maysam
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The purpose of this project is to increase the conversion efficiency to achieve the maximum of inverter in grid connected photovoltaic (PV) system in Palestine, then automatically the total cost of the system will decrease by using an iterative method to calculate the optimum size of inverter and which it is for the first time done in Palestine. The output power from PV array relies on some common parameters which is the solar radiation (G) and ambient temperature records, where (G) was taken as the frequency of global solar radiation in hours, this parameters was using it to develop a Matlab model for a PV array and inverter sizes and we made it matched with each other. The efficiency in the efficiency curve for a commercial inverters depends on the input power from PV array and inverter rated power and some coefficient called it (C1,C2, and C3) can be calculated by Matlab fitting tool, this curve divided into many parts this is due to the relation between the efficiency and the input power and inverter rated power which is a- linear or non linear, then sample of values taken from it and was used this to make curve fitting for it by Matlab fitting tool. The PV-to-inverter sizing ratio is known as the sizing ratio (Rs) which is the ratio between PV rated power to inverters rated power, it was optimized at specific load level as we used 5KW commercial inverter model. The substance of this project optimization was maximizing the annual average inverter efficiency which is depends on the daily averages of solar radiation (G) which it is depends already on hourly average solar radiation and the annual depends also on ambient temperature (T) and inverter rated power (P). In Matlab code after getting a specifications of the PV system in iterative method to know the inverter size, an iterative loop was used by a group of Rs values after defining it, then the inverter rated capacity calculated and then the output power of PV array calculated, then the hourly efficiency estimated by inverter model development to calculate the annual efficiency which is stored in certain array. This iterative still working and continue until reaching the peak (maximum) value of Rs, then find the maximum efficiency value with optimum Rs index of it, by this we was achieved the goal and the purpose of this project which is to estimate the maximum inverter’s efficiency from side of PV array output power and inverter rated power (optimum sizing ratio, Rs) for the first time in Palestine. The results displayed the values of the optimum sizing ratio of 5KW, 50KW and 100KW inverter are 1.510, 1.660 and 1.430, respectively, and the maximum conversion efficiency of the inverter are 94.9147%, 95.1561% and 95.7944%, respectively.