A Transient Stability Enhanced Andronov-Hopf Oscillator for Grid-Forming Converters

Grid forming control has been widely applied in the fields of renewable energy systems, owing to its capability to generate self-synchronous voltage and exhibit superior small-signal stability under weak grid. Andronov-Hopf oscillator (AHO) control is an emerging nonlinear controller to implement grid-forming control, while its transient behaviors under large-signal disturbances have not been fully explored. Different from the droop control with fixed droop coefficients, the transient stability of AHO-based converter under large grid disturbances will be deteriorated due to the equivalent nonlinear droop coefficients of AHO control. Therefore, this article proposes a transient stability enhanced Andronov-Hopf oscillator (EAHO) control. By reconstructing the dynamic equations of traditional AHO control, the monotonically decreasing nonlinear droop coefficients of traditional AHO control are reshaped into monotonically increasing as the voltage amplitude increases. The transient stability features of the droop, AHO, and EAHO control during grid voltage sags are compared and summarized. The theoretical analysis and experiment results show that the transient stability of EAHO control is significantly improved compared to AHO control.