Frequency Trajectory Planning Based VSC Control Strategy for Power System Frequency Regulation

To ensure frequency stability of low inertia power systems, VSC needs to provide frequency response (FR) service. Limited by predicting grid inertia/damping and disturbances that are difficult to measure, the FR performance is greatly restricted. Besides, excessive response under certain conditions results in several consequences, including 1) energy waste, and 2) the VSC power frequently and excessively deviating from steady-state points, thereby reducing the component's life, lowering system safety/reliability, and increasing the risk of VSC overcurrent faults. To solve these issues, this paper proposes the frequency trajectory planning (FTP) based FR strategy, with the fundamental idea to actively plan the frequency trajectory with necessary safety margin in accordance with the grid code. Specifically, if the system frequency locates within the range of planned one (suggesting frequency indexes satisfying the requirement), VSC remains at the steady-state point to avoid excessive FR service; otherwise, the FR service is required, and the FTP control is enabled to closely track the planned trajectory. By fulfilling the tracking purpose, the requirement on system frequency indexes is met, frequency stability is guaranteed, and the over-response is avoided. Namely, the planned trajectory can characterize whether the system requires FR service and whether the provided FR service is sufficient or excessive. Additionally, the method needs no measurement of inertia/damping and disturbances of the system, and can be directly integrated into the commonly used VSC control systems. Finally, experiments prove the effectiveness and advancement of the FTP strategy.