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This paper presents a new methodology for primary frequency response (PFR) in a microgrid through the finite control set-model predictive control (FCS-MPC) plus droop control applied to the grid side converter (GSC) of a doubly fed induction generator (DFIG). In this configuration, the rotor side converter (RSC) is responsible for maintaining wind turbine operation at the maximum power point (MPP) extraction, even at the time of a disturbance, while the GSC is responsible for processing the power required to reestablish the microgrid frequency at its rated value. The power required for frequency control comes from a battery energy storage system (BESS) connected to the DC-link, and its value is selected via the FSC-MPC by continuously adjusting the droop gain value. This control configuration has considerable benefits such as continuous operation at the MPP extraction, injection of power proportional to the frequency imbalance, the capability to impose restrictions through the control and it does not use any type of communication between the storage system and the control. Through the FCS-MPC, the gain of the droop controller is selected, which maximizes the power needed to control the frequency of the microgrid. To verify the performance of the proposed control strategy, simulations are performed for an unexpected islanding of the microgrid under different wind speed scenarios. The results show that the DFIG equipped with the proposed control strategy is able to provide ancillary services such as PFR in all DFIG operating modes.

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Abstract:The share of photovoltaic (PV) farms is increasing in the energy mix as power systems move away from conventional carbon-emitting sources. PV farms are equipped with an expensive power converter, which is, most of the time, used well bellow its rated capacity. This has led to proposals to use it to provide reactive power support to the grid. In this framework, this work presents a step-by-step methodology to obtain the reactive power support capability map and the associated technical costs of single-and two-stage PV farms during daytime operation. Results show that the use of two-stage PV farms can expand the reactive power support capability for low irradiance values in comparison to single-stage ones. Besides, despite losses being higher for two-stage PV farms, the technical cost in providing reactive power support is similar for both systems. Based on the obtained maps, it is demonstrated how the profits of a PV farm can be evaluated for the current ancillary services policy in Brazil. The proposed method is of interest to PV farm owners and grid operators to estimate the cost of providing reactive power support and to evaluate the economic feasibility in offering this ancillary service.

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