Dynamic performance of a back-to-back converter under grid disturbances with a classical DC-bus voltage control loop v.s. a DC-bus voltage control loop with Ni-Cd and Ion-Li batteries

Abstract

The aim of this paper is to present a comparative study between the dynamic response of two back-to-back converter topologies, using grid-connected Voltage Source Converters (VSC's). The first topology consists on a back-to-back converter where the DC-bus voltage is controlled by means of a classical internal DC voltage control loop. In the second topology, the DC-bus voltage is controlled by a bi-directional boost-buck DC/DC converter connected to a battery stack. In this paper both, Ni-Cd and Ion-Li battery technologies were studied. Since both topologies have a linear plant we can apply Field Oriented Control (FOC) to control both, real and reactive power exchanged with the electrical grids, as well as the DC-bus voltage. The back-to-back converter with internal DC-bus control voltage is a very well known topology which allows drive variable speed electrical machines, control electrical machines connected to the grid and decoupled reactive power flows of two different electrical grids. On the other hand, the back-to-back converter with a bi-directional boost-buck DC/DC converter connected to batteries is a more recent topology which allows decuple both, real and reactive power flows when connected to two different electrical grids. The comparison between both topologies and control methods is verified through time simulations in the discrete domain under several grid disturbances as real and reactive power steps and voltage dips. The final goal of this article is to be able to apply hot-swapping control to connect or disconnect batteries according to their State of Charge (SOC).