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In this paper a new AC/DC unidirectional switching cell with five voltage levels is proposed. It is called 5L-StackedCoupled-Inductors (5L-SCI) cell and can be connected between an AC current source and a DC voltage source. The novelty of 5L-SCI topology is based on two cascaded stages that work at different currents and different switching-frequency. The first stage contains two diodes that operate at high-current and lowfrequency. The second stage works at low-current and highfrequency and contains two stacked groups of basic switching cells parallel connected by means of coupled-inductors. An interesting property of the 5L-SCI switching cell is the use of stacked groups which work alternatively on a half-cycle. Thus, the active power devices that form the stacked groups switch only half of cycle. The operation principle of the 5L-SCI cell is verified by numerical simulations both for single-and for threephase unity-power-factor PWM rectifiers.

Abstract:The control of low power systems, which include renewable energy sources, a local network, an electrochemical storage subsystem and a grid connection, is inherently hierarchical. The lower level consists of the wind energy sources (power limitation at rated value in full load regime and energy optimization in partial load regime) and photovoltaic (energy conversion optimization) control systems. The present paper deals with control problem at the higher level and aims at generating the control solution for the energetic transfer between the system components, given that the powers of the renewable energy sources and the power in the local network have random characteristics. For the higher level, the paper proposes a mixed performance criterion, which includes an energy sub-criterion concerning the costs of electricity supplied to local consumers, and a sub-criterion related to the lifetime of the battery. Three variants were defined for the control algorithm implemented by using fuzzy logic techniques, in order to control the energy transfer in the system. Particular attention was given to developing the models used for the simulation of the distributed energy system components and to the whole control system, given that the objective is not the real-time optimization of the criterion, but to establish by numerical simulation in the design stage the "proper" parameters of the control system. This is done by taking into account the multi-criteria performance objective when the power of renewable energy sources and the load have random characteristics.