Design of Active Power Filter for a Grid Integrated Photovoltaic System

Abstract

The phrase power quality (PQ) defines good quality of voltage and current combination, satisfactory services and reliability of an electrical network at different stages i.e. generation, transmission, distribution and utilization. There are so many natural incidents (flashover, lighting etc.) as well as artificial reasons which corrupted the ac power system. The poor quality of power introduces some unwanted problems like harmonics, noise, vibrations, surge, sag/dip, swell etc. in power system network. Modern days power system is seriously affected by solid-state equipment’s due to presence of non-linearity. Therefore, elimination of harmonics and other issues are necessary to achieve a smooth and economical operation of power system. Considering the current scenario of conventional energy source, the development of photovoltaic (PV) cell is one of the best option to proper use of Renewable Energy Sources (RES).

This thesis deals with a three phase two stage grid connected PV system for PQ improvement.The mathematical modelling of a PV array, a perturb and observe (P&O) algorithm based maximum power point tracking (MPPT) controller along with the dc/dc boost converter is designed for extracting maximum power from a solar PV system. The performance of MPPT controller at different environmental conditions is verified through simulations in MATLAB / SIMULINK. The extracted power is inject ed to a grid through a Voltage Source Inverter (VSI) for PQ improvement.

An Instantaneous Reactive Power Theory (IRPT) or “p-q theory” is implemented to produce controlled pulses for VSI. Also a “d-q theory” with Proportional Resonant (PR) based another controller is designed for better performance to mitigate current harmonics. The VSI provides necessary current to the grid for current harmonics compensation. Both controller have been designed to perform in balanced and unbalanced load conditions. A second harmonic oscillation is observed in case of d-q controller which is unwanted for removing PQ issues. A noise detection based control approach determines the fundamental component of load current and is very effective for removing steady state oscillations. An adaptive DC Link voltage control technique gives an additional advantage for proper operation of VSI. The THD of grid current in case of all compensation techniques has been found well under the limit of an IEEE-519 standard.