Research for a three‐level T‐type grid‐connected converter based on the simplified three‐level SVPWM modulation scheme and neutral‐point potential balancing

Abstract

ABSTRACTT‐type pulse width modulation controlled three‐level circuit is the mainstream topology in current medium power distributed PV inverters, charging station and active power filter system with the advantages of high equivalent switching frequency, high efficiency, small filter inductance and small grid current harmonic. Aiming at the inherent problems of midpoint voltage fluctuation and complex of the traditional three‐level space vector pulse width modulation (SVPWM) scheme of a three‐level T‐type rectifier, a new equivalent method of SVPWM strategy used in three‐level converter based on acting time equivalence was proposed, which needs no trigonometric function, irrational operation, and complex coordinate transformation. By the means of rotating the target vector in other sectors to the first sector, the dwell time of vectors can be calculated by the unified formula, and the formula for calculating the dwell time is deduced based on two levels SVM. Then, the control problems of the neutral‐point voltage balance in T‐type three‐level converter topology are analyzed and studied. Through the PI control of electric charge of one capacitor, the neutral‐point voltage can be kept to be half of the DC supply voltage stably. To verify the correctness and effectiveness of the proposed control strategy, a complete simulation model and experimental prototype platform under the digital control is established. The results show that the implementation of this method is very simple and it could decrease calculation error and keep the neutral point potential balance, which makes the results more accurate. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.