New Control Strategy of an Up–Down Converter for Energy Recovery in a CDI Desalination System

Capacitive deionization (CDI) is becoming a suitable alternative for desalination. The low cost of the material required for it and the lower energy consumption can be two critical factors for the development of this technology. CDI technology does not require a high-pressure system or specific membranes to operate. The energy storage capability of CDI cells allows most of the stored energy to be recovered and used in other CDI cells. The aim of the power stage in charge of the energy recovery is to transfer the stored energy from one cell to another with the maximum possible efficiency to continue with the desalination process. With this goal this paper shows a new control strategy, in which the evolution of the current follows the efficiency of the converter. This new control improves the efficiency behavior of the converter as well as the energy recovery. The CDI modules have been electrically modeled and their electrical parameters have been defined according to the geometrical characteristics of the module. This allows the optimum geometrical parameters to be specified in order to optimize the energy storing process. A mathematical algorithm developed allows an easy simulation of the converter behavior with large input and output capacitors.