This paper analyzes the PV power plants operability improvement obtained when introducing energy storage (ES) systems which allow decoupling the power received from the sun on the photovoltaic (PV) panels from the power injected by the power plant into the grid. Two energy management strategies are presented and analyzed, using Li-ion batteries as the energy storage buffer. The generated power redistribution and its variability reduction are All the results obtained in this paper are based on one year long simulations which used real irradiance data sampled every two minutes.

This work aims at optimizing the converter design of the double-T MMC DC-DC converter in terms of transmitted power per submodule and also in terms of transmitted power per silicon area, while, at the same time, providing the capability to block dc faults. Firstly, the converter operation is described and the optimal values of the inner ac and dc voltages that minimize device power rating are derived. Next, the submodule topology is analyzed and a thorough study on the converter capability for blocking fault currents is carried out, showing that the converter is able to isolate dc faults both at the input and at the output of the converter. Finally, the previous analytical study is verified by means of detailed PSCAD simulations.

This paper proposes a dynamic current limit for modular multilevel converters (MMCs) that maximizes the injection of current during grid faults in order to mitigate the voltage dip, reduce voltage imbalances in case of an asymmetrical fault, and ensure the proper operation of protective relays. The reduced short-circuit capacity of MMCs, and power converters in general, is one of their main limitations. In the event of a fault, the converter’s current is significantly lower than that of the synchronous generators, which may impact both the performance of power system protective relays and the mitigation of voltage drops during faults. Usually, to protect the MMCs themselves, their output current is limited by their control. However, the current flowing through the power semiconductors is the arm current, not the output current, and this consists of an AC and a DC component. A new current saturation strategy aiming at maximizing fault current injection, in compliance with the most recent grid codes, is proposed. This strategy limits the arm currents by dynamically adjusting the output current limit while injecting reactive currents (both positive- and negative-sequence) and active current according to the grid codes, the fault type, and voltage sag level. A theoretical analysis is carried out to determine the maximum current injection that will not exceed the arm limits, and this is then validated through detailed PSCAD simulations. With the proposed strategy, the supplied current can be increased by approximately 40%.