Improved Grid Forming Control for Energy-Type STATCOM to Enhance Damping and Limit Multiple Currents

To improve the frequency and voltage stability of the modern power system, an energy-type STATCOM (ET-STATCOM) formed by embedding supercapacitors (SCs) in the dc bus of two film capacitor-type STATCOMs was designed, which can provide virtual inertia by boosting active power and voltage support through reactive power compensation. However, the issue of its grid forming control hangs in the balance. First, the favored virtual synchronous machine control may lead to over-charge/-discharge of SCs due to the active power-based control target. Second, although the classical matching control (MC) can regulate SC energy, none of its existing damping enhancement schemes is proper for the ET-STATCOM. Last but not least, the existing current limiting strategies can only limit the total current magnitude synthesized by the active and reactive currents, but not their respective magnitudes. To address these issues, an energy synchronization link founded on the MC and a novel damping enhancement scheme based on active power direct feedback are proposed, which helps the ET-STATCOM to integrate self-synchronization with power oscillation suppression capability, spontaneous inertia response, and autonomous management of SC energy. In addition, a multicurrent limiting control technique has been investigated to achieve overall and independent limiting of active and reactive currents. Simulations and a practical 35kV/30MVar/3MW/4s prototype validate the method's effectiveness.