| Abstrakt: |
The system examined in this paper is a hybrid doubly-fed induction generator wind-turbine (DFIG-WT) combined with a battery energy storage system (BESS). It operates in both stand-alone and grid-connected modes, with the capability for seamless transitions between these states, and manages the state of charge (SOC) of the battery under all conditions. In this paper, by modifying control structures of the rotor-side and grid-side converters (RSC and GSC), the RSC is controlled in the grid-following (GFL) mode and the GSC in the grid-forming mode using the virtual synchronous generator technique. The proposed control scheme with detailed considerations for both the RSC and GSC simultaneously addresses the following aspects: (a) seamless operation in both grid-connected and stand-alone conditions, (b) synchronization and smooth connection of the DFIG during initial moments of grid-connection without using a phase-locked loop (PLL), (c) enabling the converters control systems to allow the grid-connected DFIG to operate not only in MPPT mode but also in power dispatch mode based on the power grid requirements, and (d) SOC adjustment of the battery in both grid-connected and islanded modes. In the grid-connected state, the battery SOC is managed by the GSC, and for SOC < 90 %, the battery is charged by the GSC according to the SOC level, and for SOC > 95 %, the GSC limits the SOC below the upper limit. In the stand-alone state, the SOC upper limits are mainly managed by the RSC, and if the SOC exceeds the value of 85 %, the RSC works in the power curtailment mode and reduces the stator power. |
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