Design and Implement a Grid Forming Inverter with Low Harmonic Current Control

This paper proposes a control strategy suppressing 5<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> and 7<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonics. Using Park's Transformation, the high-order harmonics of the grid can be extracted separately. The compensation current is then fed back into the grid to eliminate the harmonic components following the use of a controller and active power filter. This topology uses a 3-phase, three-level neutral point clamped inverter as the realization circuit of the active power filter. Compared with the conventional two-level inverter, this topology has the advantages of lower harmonic distortion and more minor switching voltage stress. Furthermore, SiC MOSFETs with lower conduction loss and switching losses are used as the main power switches to improve system efficiency. Finally, an experimental prototype inverter controlled by DSPTMS320F28335 is implemented with a rated power of 7.2kW, input voltage of 800 V, output voltage of 220 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</inf> for each phase, switching frequency of 40 kHz, and line frequency of 60 Hz to verify the feasibility of the theory. The experiment results show that the 5<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> and 7<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic current is reduced to 3.26% and 3.48%, respectively, when added harmonic suppression control. Furthermore, the THD of the grid without compensation is 31.05%, and the THD after the 5<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> and 7<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> compensation is 5.41%.