An Artificial Intelligence Based Grid Tied SPV System with Adaptive DC Link Voltage for CPI Voltage Variations

Abstract

This proposed model deals with a three-phase two-stage grid tied SPV (solar photo-voltaic) system. The first stage is a boost converter, which serves the purpose of MPPT (maximum power point tracking) and feeding the extracted solar energy to the DC link of the PV inverter, whereas the second stage is a two-level VSC (voltage source converter) serving as PV inverter which feeds power from a boost converter into the grid. The aim of this controller is to achieve an optimum MPP operation without the need of atmospheric conditions measurements and to enhance the efficiency of the PV power system. This model  also uses an adaptive DC link voltage which is made adaptive by adjusting reference DC link voltage according to CPI (common point of interconnection) voltage. The adaptive DC link voltage control helps in the reduction of switching power losses. A feed forward term for solar contribution is used to improve the dynamic response.

                A photovoltaic (PV) system is able to generate wide ranges of voltage and current at terminal output. However, a PV cell is required to functionally maintain a constant direct current (DC) voltage at a desired level during real-time variations . To obtain this goal, a DC/ DC converter together with control scheme topology is used. An adaptive PI control scheme is proposed to stabilize the output voltage of the DC/DC converter, in order to maintain and stabilize the Adaptive DC-link voltage accordingly to the changes of voltage at the Common Point of Interconnection before the  grid.

                The Point of Common Coupling is a point in the electrical system where multiple customers or multiple electrical loads may be connected. This should be a point which is accessible to both the utility and the customer for direct measurement. Large numbers of small scale solar photovoltaic (PV) systems  are being connected to the distribution level of the power grid PV systems are integrated to the power grid via power electronic converters.  The model is tested considering realistic grid voltage variations for under voltage variations. This model is advantageous not only in cases of frequent and sustained under voltage (as in the cases of far radial ends of Indian grid) but also in case of normal voltages at CPI. The THD (total harmonics distortion) of grid current has been found well under the limit of an IEEE-519 standard. The validation of the proposed MPPT controller is shown by MATLAB/SIMULINK simulation.