Study and evaluation of distributed power electronic converters in photovoltaic generation applications

This research project has proposed a new modulation technique called “Local Carrier Pulse Width Modulation” (LC-PWM) for MMCs with different cell voltages, taking into account the measured cell voltages to generate switching sequences with more accurate timing. It also adapts the modulator sampling period to improve the transitions from level to level, an important issue to reduce noise at the internal circulating currents. As a result, the new modulation LC-PWM technique reduces the output distortion in a wider range of voltage situations. Furthermore, it effectively eliminates unnecessary AC components of circulating currents, resulting in lower power losses and higher MMC efficiency.Departamento de Tecnología ElectrónicaDoctorado en Ingeniería Industria

Local Carrier PWM for Modular Multilevel Converters with Distributed PV Cells and Circulating Current Reduction

Producción CientíficaA new topology has been recently proposed for grid-connected photovoltaic (PV) systems, using modular multilevel converters (MMCs) and distributing PV panels throughout the MMC cells. This topology has two main advantages: it reduces the power losses related to moving the energy into the MMC capacitors from an external source, and it removes the losses and costs related to the DC to DC converters used to track the maximum power point on string converters or central converters, because that task is delegated to MMC cells. However, traditional pulse width modulation (PWM) techniques have many problems when dealing with this application: the distortion at the output increases to unacceptable values when MMC cells target different voltages. This paper proposes a new modulation technique for MMCs with different cell voltages, taking into account the measured cell voltages to generate switching sequences with more accurate timing. It also adapts the modulator sampling period to improve the transitions from level to level, an important issue to reduce the internal circulating currents. The proposed modulation has been validated using simulations that show a consistent behavior in the output distortion throughout a wide operation range, and it also reduces the circulating currents and cuts the conduction losses by half. The behavior of this new topology and this new modulation has been compared to the mainstream topology with external PV panels and also to a fixed carrier modulation

MMC-based topology for grid connection of wind generators with phase and arm power balancing

Producción CientíficaA new topology of a wind farm wherein the wind generators are integrated into the structure of a modular multilevel converter (MMC) is presented. It allows connecting a group of small/medium size wind turbines to the grid, replacing all the grid side converters of the wind generators by the MMC. The different power generated by each wind generator causes power imbalances that can lead to circulating currents; this paper addresses this problem by analyzing it in a simple way. The analysis shows that power differences between phases are naturally balanced by the DC component of circulating current, without the need to use a specific regulator. However, the power differences between the arms result in a high 50 Hz circulating current. This paper presents the design of a new regulator that corrects these power imbalances by generating a phase difference between the upper and lower arm voltages resulting in an optimal 50 Hz circulating current. The operation of the MMC-based wind farm topology has been tested when all the turbines generate the same power and when they generate significantly different powers. Numerical and real-time simulation results show that the proposed regulator keeps the powers of the MMC phases and arms balanced

PID_20_21_071_Anexos_V2

Durante el curso 2020/21 el Grupo de Innovación Docente en Electrónica de Potencia de la UVa (GIDEPUVa) apostó por una metodología presencial de Aprendizaje Basado Proyectos (ABP), sin embargo, debido a la incertidumbre sanitaria de los últimos meses en este PID se ha trabajado para impartir la metodología de ABP en modalidad on-line. Para planificar la actividad docente en una asignatura bajo la metodología de ABP on-line existen diferentes aspectos que se deben tener en cuenta, los cuales conducen a los objetivos que se han trabajado en este PID. Se ha trabajado en la planificación de experiencias de ABP on-line y el establecimiento de un procedimiento que permita asegurar que la carga de trabajo de esta metodología fuera la apropiada. El segundo de los objetivos de este PID fue trabajar en el diseño de herramientas hardware de bajo coste que pudieran ser empleadas por los estudiantes para lograr los objetivos de aprendizaje en formación bimodal o incluso on-line. En el tercer y cuarto objetivo de este PID se trabajó en la búsqueda de procedimientos que garantizarán, en un escenario de docencia on-line o bimodal, que los estudiantes dispusieran de un sistema de tutorías y de unas estrategias de evaluación.Departamento de Tecnología ElectrónicaProyecto de innovación docente PID 2020/21 071 y anexos correspondinetes