Grid Integration of Renewable Energy Generating System Using Nonlinear Harmonic Observer Under Non-Ideal Distribution System

Abstract

The renewable energy sources (RESs) are intermittent in nature with high availability based uncertainties. These resources when integrated to the utility grid significantly hinder the grid power quality (PQ). This paper deals with a topology including grid connected renewable energy generating system, which is a combination of wind turbine (WT) driving the synchronous generator (SG) and solar photovoltaic (PV) array associated at the DC link eliminating the DC-DC converter stage via a common DC link with PQ improving control scheme. The variable revolutions per minute (RPM) operation is achieved by the back to back connected grid side VSC (GVSC) and machine side voltage source converter (MVSC). The regulation of MVSC, is achieved by the vector control. The GVSC is controlled by employing the nonlinear harmonic observer (NHO) control. It provides robust implementation under various perturbations faced practically i.e. discontinuous jump of frequency, phase and amplitude. The fundamental load current component is effectively extracted. NHO control is deployed within the framework to allow the system to dynamically adapt to the changes in the operating environment while maintaining the PQ of the utility grid. A special attention is paid to the condition when the power generated by solar PV array is zero (during night operation) and the GVSC acts in the distribution static compensator (DSTATCOM) mode fulfilling the reactive power requirement. Independent optimal power extraction (OPE) techniques are featured for both wind and solar PV array. Test conditions are realized on the laboratory developed prototype and the test results are acquired for PQ, loss of supply from solar PV array, effects of randomness of the wind speed and solar insolation along with load alterations.