The connection of low power renewable energy sources, such as fuel cells, to the distribution generation system requires power electronics structures with high voltage gain, high capability to power processing and consequently, high levels of current flowing through the dc/dc converter. In this context, this study analyses how the parasitic resistances of the passive components and the load power demand affect the dc/dc converter voltage gain. Taking into account the mathematical model, the boundaries of operation of the Interleaved Boost with Voltage Multiplier converter is determined through a set of equations and by means of a graphical analysis. The theoretical analysis, simulations and experimental results are used to validate the proposed approach presented in this study.
This paper presents an adaptive powersharing methodology for management of dc microgrids powered by fuel cell (FC) and storage system (SS). In this context, the use of an adaptive k-sharing function in the control scheme is proposed to compensate the fast transients on the ac-side and manage the power sharing at steady-state regime between the FC and SS. The adaptive k-sharing is implemented with a low-pass filter transfer function for the FC and a complementary transfer function associated with the adaptive k-sharing gain for the SS. The proposed adaptive k-sharing function links the FC and the SS dynamics with the management of the dc microgrid, ensuring that the entire FC operation is performed in accordance with its operational limits. One of the main advantages of the proposed adaptive k-sharing is to reach high levels of stability and minimum disruptions on the FC terminals. To evaluate the feasibility of the proposed approach, we analyze the k-sharing behavior to determine the operational limits of the dc microgrid. Finally, to support the theoretical analysis we carried out a set of experimental results.
The connection of distributed generation systems powered by fuel cells (FCs) to the grid requires power electronics devices with high voltage gain, high capability of power processing and high levels of current absorbed from the direct current (dc) source. In this context, the authors propose the use of an interleaved boost with voltage multiplier (IBVM) converter connected to a FC and a voltage source inverter (VSI) to form a micro grid. To manage the power delivered by the FC in gridconnected operation, they propose two different control structures, mode 1 (FC cascade control) and mode 2 (controlling FC operating point). In mode 1, the dc-link voltage is adjusted by the dc/dc converter, while the injected current is controlled by the VSI. On the other hand, in mode 2, the VSI is responsible to keep the dc-link stable, while the dc/dc converter controls the current injected into the grid by means of the FC current reference. Since the VSI control structure has been exhaustively investigated in the literature, in this study, they evaluate the impact of the proposed control structures in the dc-side and also the IBVM efficiency. Finally, they conclude the study outlining the main points discussed.
This study presents a control strategy for managing power delivered to, or absorbed from, the grid, independent of local load or grid characteristics. To achieve this objective, the strategy requires the use of three levels of control structures. The first is related to phase-locked loop and grid-tie algorithms, which are employed to minimise disturbances during the grid connection. The second, which produces voltages with reduced harmonics levels at the distributed generation (DG) terminals, comprises the cascade voltage and current control. The third structure is the active and reactive power control mechanisms, which uses the angle of displacement and the adjusting of the DG voltage amplitude to keep the power flow through the grid at a specific set-point, independent of local load characteristics. In addition, the power control structures have to operate in a decoupled operation mode, whereby the active power control has to be faster than the reactive power control, or vice versa. In terms of their physical structure, a passive LCL filter is used to connect the voltage source inverter to the grid. To verify the findings and observations discussed in this study, a set of simulations and experimental results are presented.
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