DESIGN, ANALYSIS AND DIGITAL CONTROL OF GRID CONNECTED INVERTERS

Abstract

Currently, the control of grid connected inverters is an appealing area of research. There exists several control schemes, but this thesis primarily focuses classical control (P/PI) of grid tied inverters under diverse variations such as LCL filter parameter values and grid impedance. The performance of conventional classical PID controller renders down resulting in a large steady state error; high THD level in the output current and in its worse scenario destabilizes the designed system if controller gains are not seleted properly. To achieve efficient results proper tuning of gain parameters is necessary for small steady state error with very low level of THD in the output current. This thesis investigates the limitations of a conventional PID controller considering stability and system response by changing the controller gains in conjunction with LCL filter parameters. The controller gain is varied within permissible range of bandwidth of the system while maintaining the steady state response, frequency response and overall efficiency under strong grid harmonics. The MATLAB/Simulink results are incorporated for the proper analysis of controller behavior with stability range under the influence of grid impedance variations.