Configuration and control strategy for an integrated system of wind turbine generator and supercapacitor to provide frequency support

Wind turbine generators (WTGs) can provide fast frequency support to power systems through inertial control via the release of kinetic energy stored in rotating masses. However, because the kinetic energy is limited, the frequency support from WTGs based on inertial control cannot last until the system frequency recovers to the nominal value. Thus, it must be terminated during system frequency control, which results in adverse effects on the system frequency response. To guarantee sufficient energy and fast response for the frequency support of a permanent magnet synchronous generator based WTG, this study proposed the integration of a DC/DC converter-interfaced supercapacitor (SC) at the DC link of the WTG and consequently formed an integrated system of WTG and SC (WTG-SC system). First, the configuration of the SC was proposed based on the evaluation of the energy consumption of the WTG-SC system for frequency support and the available kinetic energy of the WTG. Second, a control structure that coordinates the machine-side converter (MSC), grid-side converter (GSC), and DC/DC converter of the SC was proposed. Finally, a “dual-droop” frequency support control scheme for the WTG was proposed to enhance the WTG-SC system’s frequency support capability and the efficiency of energy utilisation during frequency support. The efficacy of the proposed approach was validated using a modified IEEE 39 bus system with a wind farm comprising 100 WTG-SC systems under different operating conditions.