Enhanced Shunt Active Power Filter based on Instantaneous Power Theory Used in Microgrids under Non-Ideal Grid Voltages

In microgrids, load variation and non-linear loads cause distortion in currents and voltages due to the low mechanical inertia of the system. Using a shunt Active Power Filter (shunt APF) based on instantaneous power theory also known as p-q theory is a solution to compensate current harmonics. Accurate functionality of p-q theory requires pure sinusoidal grid voltage waveforms. Under non-ideal grid voltage conditions, correct voltage references must be estimated. This paper presents a modified strategy to alleviate the problem. The proposed method is based on making virtual d-axis voltage in the synchronous reference frame. All the assumptions and principles of the proposal are described in details. The concept has been validated by simulations in various cases and compared to the most common method i.e. using low pass filter.