Transient Stabilization Control of Electric Synchronous Machine for Preventing the Collapse of DC-Link Voltage

Electric synchronous machine (ESM) control is a power synchronization strategy that utilizes the measurement of dc-link voltage to generate a frequency reference. By using ESM, the grid-connected inverters with indeterminant renewable energies can work in grid-forming mode, and realizes a closed-loop control of the dc-link voltage. However, under weak grid conditions, the ESM provides a sluggish performance for the regulation of dc-link voltage and is prone to the transient instability issues, including dc-voltage collapse and synchronization instability, which hinders the application of ESM. This paper reveals the instability mechanism of dc-link voltage under large disturbances, and proposes a passivity-based control for the transient stabilization of ESM. Firstly, the transient stability of ESM is analyzed from the view of port-Hamilton system. The corresponding energy function comprises the energy stored in dc-link capacitor and potential energy in ac side. Then, a 2-degree-of-fredom controller is proposed to stabilize the dc-link voltage by enhancing the energy dissipation. It combines a phase-shift controller and supplementary voltage controller, fully utilizing the control flexibility of the inverters. Dissipation analysis proves the large-signal stability of the proposed control. Simulations and hardware-in-the-loop (HIL) experiments validate its transient performance in a single-inverter-infinite-bus (SIIB) system and a multi-inverter test system.