Phase Compensator Placement and Design for Subsynchronous Oscillation Damping of Multi-loop Grid-Forming Converters

Under stiff grid conditions, grid-forming (GFM) converters are prone to subsynchronous oscillations (SSOs). Phase compensators are widely used as effective means to address SSO issues. However, owing to the lack of precise design regarding the location and configuration, the performance of phase compensators within multi-loop GFM control remains underutilized. To this end, the performance of the phase compensator is quantitatively evaluated by the negative damping area in the impedance model. With a parametric analysis of this area, the SSO-critical control loops and governing parameters are pinpointed, thereby identifying four optimal embedding locations for compensators. To effectively demonstrate the robustness of SSO damping under varying grid conditions, the required configuration properties of the compensator for each location are proposed, and a feasible and general compensator form is provided. Furthermore, the proposed design proves effective in a model incorporating frequency coupling. The hardware-in-loop (HIL) experimental results validate the theoretical insights as well as the effectiveness and robustness of the presented damping strategy. The systematic design framework can be adapted to guide the phase compensator in diverse multi-loop GFM controllers for effective SSO damping.