Ancillary Services to Mitigate Non-linear and Unbalanced Load Based on CPT Using a DFIG Power Plant

The increase of renewable energy sources and non-linear loads on the utility grid introduces challenges in maintaining the nominal conditions of the utility grid. A viable approach to addressing some of these challenges is to utilize renewable energy conversion systems that accomplish supplementary functions in addition to supplying active power. This paper presents the implementation of ancillary services to mitigate non-linear and unbalanced loads using a single Doubly Fed Induction Generation (DFIG) power plant. For this, the Conservative Power Theory (CPT) is used to provide three types of services simultaneously: active filtering, reactive power compensation, and unbalanced phase compensation. A back-to-back converter is used to control the power flow in the DFIG and employ ancillary services. Two control strategies are compared: in the dq reference frame and the $\alpha \beta$ reference frame. Simulations in MatLab/Simulink are used to evaluate the response of the CPT and the control strategies. The ancillary services performance is analyzed using the indicator based on standards and CPT factor. The results show that the indicators comply with the standards depending on the active power supply. Moreover, $\alpha\beta$ reference frame exhibits better performance than $dq$ reference frame.