Elimination of the State-of-Charge Errors for Distributed Battery Energy Storage Devices in Islanded Droop-controlled Microgrids

Abstract

Battery energy storage devices (ESDs) have become more and more commonplace to maintain the stability of islanded power systems. Considering the limitation in inverter capacity and the requirement of flexibility in the ESD, the droop control was implemented in paralleled ESDs for higher capacity and autonomous operation. Under the conventional droop control, state-of-charge (SoC) errors between paralleled ESDs is inevitable in the discharging operation. Thus, some ESDs cease operation earlier than expected. This paper proposes an adaptive accelerating parameter to improve the performance of the SoC error eliminating droop controller under the constraints of a microgrid. The SoC of a battery ESD is employed in the active power droop coefficient, which could eliminate the SoC error during the discharging process. In addition, to expedite the process of SoC error elimination, an adaptive accelerating parameter is dedicated to weaken the adverse effect of the constraints due to the requirement of the system running. Moreover, the stability and feasibility of the proposed control strategy are confirmed by small-signal analysis. The effectiveness of the control scheme is validated by simulation and experiment results.

Optimal Power Control Strategy for Wind Farm with Energy Storage System

“…At the beginning of each hour, the proposed searching process is executed to determine the optimal filter time constant. Initially, the previous value of filter time constant is used to determine the power flow of the system in (19) and (20). If the dispatch power does not satisfy the FMR defined in (4), the filter time constant value in the previous dispatching interval hour may be too small; the filter time constant should then be increased until the dispatch power satisfies the FMR.…”

“…(19) and (20) represent the model of the proposed power flow control scheme based on the zerophase LPF. It can be seen that the filter time constant determines the ESS power and the dispatch power.…”

“…In order to comply with the grid code requirement, the wind power fluctuation must be mitigated sufficiently to ensure that the dispatch power has a fluctuation lower than the -min to meet the load demand of the grid [18]- [19], the ESS in wind power application is used to compensate the wind power fluctuation as an energy buffer. Fig.…”

Cell Balancing Method in Flyback Converter without Cell Selection Switch of Multi-Winding Transformer

“…As each cell has unequal properties such as capacity, ESR and self-discharge current, cell voltages can become unbalanced as the charging and discharging sequences are repeated in the series connection configuration [9][10]. Even though the BMS prevents safety problems associated with the unbalanced state, the available capacity of the battery or super-capacitor pack may be dramatically reduced, as the BMS applies upper and lower limits to the highest and lowest voltage cells [11][12][13][14][15]. Fig.…”