Convertidor CA/CC polifásico modular con alto factor de potencia y aislamiento galvánico, basado en emuladores de resistencia

XXIII Seminario Anual de Automática, Electrónica Industrial e Instrumentación 2015 (SAAEI’16), Elche (España)Este artículo describe un convertidor CA/CC polifásico modular con alto factor de potencia y aislamiento galvánico, cuyo principio de funcionamiento se basa en el uso de emuladores de resistencia (ER). Un ER es a su vez un convertidor que se comporta, a determinadas frecuencias, como una resistencia positiva en su puerto de entrada. El valor de esta resistencia (que es la impedancia de entrada del convertidor) depende del ciclo de trabajo de dicho convertidor. En la topología que se propone, todos los ER son controlados por una señal única para presentar la misma impedancia de entrada y el valor de esta impedancia de entrada es determinado por un lazo de control que garantiza que la tensión de salida del convertidor CA/CC completo es la deseada. La potencia de este último convertidor es la suma de las potencias procesadas por cada uno de los ER (que es la misma en todos ellos), lo que permite la construcción de un convertidor modular. Además, las funciones de un ER individual pueden ser realizadas por varios ER conectados en serie y/o en paralelo, compartiendo por igual tensiones y corrientes, permitiendo así extrapolar la idea aquí propuesta a convertidores de gran potenci

High power factor modular polyphase AC/DC converters with galvanic isolation based on Resistor Emulators

This work has been supported by the Spanish Government under Project MINECO-13-DPI2013-47176-C2-2-R and the Principality of Asturias under the grants “Severo Ochoa” BP14-140 and BP14-85 and by the Project FC-15-GRUPIN14-143 and by European Regional Development Fund (ERDF) grants.This paper deals with a modular, isolated-output, polyphase, AC/DC converter based on the use of Resistor Emulators (REs). A RE is a DC/DC converter that behaves as a resistor at its input port. The value of this resistor (input impedance) is controlled by the converter duty cycle. In the proposed topology, all the REs are controlled to have the same input impedance, whose value is determined by the outputvoltage feedback loop. Also the power processed by each RE is the same. As a consequence, the total power is distributed (and also the power losses), thus allowing us to build a modular system. Moreover, the behavior of these DC/DC converters as REs also allows their connection in series and/or in parallel with perfect sharing of voltage (when connected in series) and current (when connected in parallel). This fact makes possible to extend the proposed solution to high power applications

Digital implementation of the feedforward loop of the asymmetrical half-bridge converter for LED lighting applications

The Asymmetrical Half Bridge converter (AHBC) has proven to be a promising candidate for LED lighting applications. It provides high efficiency, galvanic isolation and, at the same time, its output filter can be very small and, therefore, easily implemented without electrolytic capacitor. On the other hand, its main drawback is its poor attainable bandwidth. In any ac-dc LED lighting application, the input voltage of the AHBC is provided by a Power Factor Corrector (PFC) converter which has to be also implemented without electrolytic capacitor in order to assure the long lifetime of the whole LED driver. As a consequence, its output voltage (input voltage of the AHBC) is affected by a low-frequency ripple. Due to the poor bandwidth of the AHBC, this voltage ripple will be transferred to the converter output voltage, leading to flickering. A possible solution is using a feedforward loop for cancelling the effect of this low-frequency ripple without affecting stability. Due to the complex and non-linear transfer function of the AHBC, any analog feedforward loop has to be tuned for a given operating point, leading to a poor performance (i.e., high flickering, high ripple) when the AHBC moves away from that point. Dimming, which is a very frequent requirement in many LED drivers, implies large variations of the output voltage and, consequently, moving away from the aforementioned operating point. In this paper, a digital feedforward loop is proposed in order to solve this problem. The digital implementation allows the feedforward loop to perfectly cancel the ripple under any condition (e.g., output voltage variation due to dimming). Besides, despite its complex transfer function, this digital feedforward loop has been designed and optimized for its implementation in small-size microcontrollers. Experimental results with a 40-W prototype prove the usefulness of the proposed feedforward loop and the validity of the equations used in the optimized desig