| Popis: |
In recent years, virtual inertia algorithms are mostly applied to inverters of high-penetration distributed generation systems to improve system equivalent inertia. When distributed generators (DG) based on traditional first-order virtual inertia (TFVI) algorithm operates in weak grid connected mode, there is contradiction between its output active power steady state and dynamic characteristics adjustment. Although the virtual inertia with improved structures such as first-order virtual inertia based on differential compensation (DCFVI) and second-order virtual inertia (SVI) have better active power control accuracy and power oscillation damping ability simultaneously, its frequency support ability in high permeability distributed generation system is weaker due to its fast frequency response and small inertia in the initial stage of response, which is easier to cause under-frequency load shedding. In this paper, firstly, the frequency characteristics of the DG based on the above virtual inertia algorithms operating in islanded mode are analyzed, and the active power steady-state and dynamic characteristics of the DG operating in grid connected mode are studied as well. Afterwards, based on the active power steady-state and dynamic characteristics comparison and summary of DG grid-connected system with each improved virtual inertia algorithm, through optimization of the second-order virtual inertia structure, an optimized second-order virtual inertia (OSVI) algorithm is proposed, which can not only maintain the active power control accuracy and suppress power oscillation, but also can provide larger frequency support capability. Finally, the effectiveness of the proposed control strategy is verified by simulation. |
