Electric springs for improving transient stability of micro-grids in islanding operations

Micro-grids fed with small synchronous generators and intermittent renewable power sources are generally considered as weak power grids unless very large energy storages are incorporated as the energy buffer. Auxiliary techniques are needed to improve their stability when transient interrupts occur. In this paper, the 3-ph Electric Spring (ES) is studied to improve the stability of the micro-grid in transient operations. The power compensation characteristics of the 3-ph ES are firstly analyzed. The linear relationships between decoupled d and q components of ES voltage and real and reactive power of smart load enable the ES to conduct frequency and voltage regulation simultaneously. The f-V_esd and V-V_esq droop control is further developed to coordinate the operation of multiple ESs distributed along a distribution line. The transient stability issues of the micro-grid under study are analyzed in detail. Simulation results show that the 3-ph ES implemented with f-V_esd and V-V_esq droop control can react swiftly to fast transient changes of micro-grids including intentional islanding, unintentional islanding, and sudden load changes.