Decoupled digital control of a three-phase four-leg inverter to feed balanced and unbalanced loads

[ES] Este trabajo presenta una estrategia de control digital para inversores trifásicos de cuatro piernas, para cumplir con el requerimiento de normas internacionales de calidad de energía para UPS cuando se alimentan cargas equilibradas y desequilibradas. La estrategia de control propuesta se desarrolla en el marco de referencia dq0 en tiempo discreto, posee un lazo interno para controlar la corriente de los inductores y un lazo externo para controlar la tensión de salida. Se demuestra que utilizando controladores convencionales pueden desacoplarse las variables de los ejes d y q, lo que permite diseñar los controladores del lazo externo de control de tensión como sistemas SISO independientes, cumpliéndose los requerimientos de régimen transitorio y de régimen permanente impuestos por norma. Para mejorar el desempeño del inversor cuando se alimentan cargas desequilibradas, se propone utilizar un controlador Proporcional-Resonante únicamente en el lazo interno del eje 0, lográndose una estrategia de control simple y de bajo costo computacional. Se presentan resultados de simulación y experimentales que permiten validar la estrategia de control propuesta.[EN] This paper presents a digital control strategy for three-phase four-leg inverters to meet the requirements of international power quality standards for UPS, when balanced and unbalanced loads are feeding. The proposed control strategy is developed in the discrete-time dq0-reference frame. It has an inner current loop to control the inductors currents and an outer voltage control loop. The analysis of this paper demonstrates that using conventional controllers, the voltages of d and q axes can be decoupled, into the whole operating range, which allows the outer voltage controllers to be designed as independent SISO systems, meeting the requirements of the transient and permanent regimes imposed by Standards. To improve the performance when the inverter feeds unbalanced loads, this paper proposes to use a Proportional-Resonant controller only in the inner loop of the axis 0, achieving a simple control strategy and, consequently with a low computational cost. Simulation and experimental results allow validating the proposed control strategy.Este trabajo fue soportado por la Secretaría de Ciencia y Técnica de la Universidad Nacional de Río Cuarto (SeCyT, UNRC), la Agencia Nacional de Promoción Científica y Tecnológica (FONCyT) a través del proyecto PICT 1663/2016 y la Red MEIHAPER CYTED.Oggier, E.; Botterón, F.; Oggier, G.; García, G. (2020). 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