Abstract
DC microgrids are gaining more attention compared to AC microgrids due to their high efficiency and uncomplicated interconnection of renewable sources. In standalone DC microgrid, parallel-connected converters connect the storage system to the load. To achieve equal current sharing among parallel converters, several methods have been presented, but they vary in their current sharing performance, complexity, cost, and reliability. In DC microgrid, the conventional droop control method is preferred because it is more competitive in terms of cost, suitability, and reliability compared to the master-slave control method. However, the conventional droop method cannot ensure equal current sharing due to the mismatches in parameters of parallel-connected converters. To address this limitation, a control algorithm that supervises a modified droop method to achieve precise current sharing between parallel modules is proposed in this paper. The control algorithm is based on the percentage of current sharing for each module to the total load current. The output current measurement of each converter is compared to the total load current and is used to modify the nominal voltage for each converter. The effectiveness of the proposed algorithm is verified by MATLAB simulation model and experimental results.
Highlights
Introduction eDC microgrid has attracted attention in recent years because it provides a more efficient integration of distributed renewable energy and storage systems, partly due to the elimination of the rectification and inversion stages [1, 2]
In a standalone DC microgrid, the renewable energy sources and storage systems provide uninterrupted power to the load. e schematic diagram of a conventional PV system with a storage battery system is shown in Figure 1, which includes two categories of converters, namely, the renewable side converter and the storage side converter. e renewable side converter interconnects the renewable energy source to the storage system, and its objective is to extract the maximum power from the renewable energy source through the maximum power point tracking (MPPT) unit, whereas the purpose of the storage side converter is to regulate the voltage of the common DC bus to the nominal value through a voltage regulator unit [3]
One of the challenges in employing parallel operation of DC-DC converters is to ensure that the load is shared between the parallel converters while maintaining acceptable voltage regulation
Summary
E percentage of current sharing (PCS) for converter i is calculated based on the measurements of the total load current and the output current of converter i as PCSi. e proposed algorithm can achieve precise current sharing between parallel-connected converters. ΔVCA is chosen to be small and the droop gains for both converters are selected to produce negligible oscillations in the output current waveforms around the desired operating points.
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