Estudo e projeto de um inversor trifásico quatro braços

Abstract

This work presents the study, design, dimensioning, and experimental validation of a four-leg, three-phase inverter, an advanced topology that is crucial for controlling four-wire systems (threephase systems with neutral). The main objective is to develop a three-phase four-leg DC/AC converter with an LC output filter for off-grid photovoltaic generation applications. The project began with the rigorous state-space modeling of the system, a fundamental step for precise dimensioning and for understanding the converter’s dynamics, including the effects of parasitic resistances present in the LC output filter. The adopted modulation strategy is three-dimensional Space Vector Modulation (3D-SVM). The complexity of this technique was handled by detailing the mapping of the 24 tetrahedra and by creating efficient algorithms for locating and limiting the reference voltage vector. The closed-loop control is implemented using a Proportional–Resonant (PR) controller. The choice of the stationary αβγ reference frame for operating this controller was strategic, as it enables precise control of positive, negative, and, crucially, zero-sequence (γ) components essential for the inverter’s fourth leg while also reducing computational effort. The PR controller was tuned analytically and then discretized using the Tustin method for implementation on a digital platform. The project was fully validated through a comprehensive set of experimental bench tests. The obtained results confirmed the high fidelity of the theoretical model, demonstrating that both the hardware and the control operate as expected. Under nominal operating conditions and for a total power of 2.2 kW, the inverter achieved a maximum total harmonic distortion of 1.25% per phase and a maximum steady-state phase voltage error of 2.20%. Specific tests, such as zero-sequence and overmodulation tests, validated the robustness and accuracy of the implemented SVM algorithms. Load imbalance, voltage imbalance, and abrupt disturbance tests confirmed the effectiveness and robustness of both the PR controller and the four-leg topology in their primary role: independently regulating phase voltages and compensating asymmetries, thus fulfilling all the objectives proposed for this work. In general, based on the obtained results, it is possible to conclude that integrating the four-leg topology with PR control in the αβγ reference frame is an efficient and robust solution for inverters in four-wire systems, delivering excellent power quality even under unbalanced operating conditions.