Diseño y simulación del control de un transformador de estado sólido de tres etapas con entrada monofásica y salida monofásica basado en un convertidor dc-dc de doble puente activo y un convertidor ac-dc multinivel de puentes en cascada

Abstract

This paper presents the design of a Solid State Transformer (SST) and its controller, and the respective tests in order to verify its correct operation. The SST designed has the potential to become a fundamental part of the Smart Grid model. It is able to keep output voltages at each stage within a tolerable range of operation, while at the same time handle disturbances common to power systems. The developed model consists of three stages: the first stage is an AC to DC converter or rectifier that convert the grid voltage to DC voltage, but this voltage is delivered in four levels by using a cascaded diode multilevel converter scheme; this is followed by a DC to DC block with three Double Active Bridges (DAB) whose function is to reduce the voltage level to an specific DC nominal value to enable its integration with alternative energy sources; finally, an inverter block convert the DAB’s output voltage into two 110 AC nominal voltage circuits that is used for distribution purposes. Between each block pair there is a DC linkage: a High Voltage DC Link for the connection from the rectifier to the DAB block and a Low Voltage DC Link for the connection of the DAB block with the inverter. Lastly, each block has its own control loop required providing stability and an acceptable operating range to the SST. This control loop operates on the switching signal or modulation index that is used in each converter. Results of the simulations by stages and from the different tests proved the correct operation of the STT.