Model-Free DPC of Grid Connected Converters Under the Weak Grid Condition

When a converter is connected to a weak grid, the system may become instable. In particular, a weak grid can lead to voltage fluctuations at the point of common coupling (PCC) and consequently causes converter instability. Thus, maintaining the stability of such systems is an important concern for the power industry. In this paper, impacts of system parameters on the stability of voltage source converters are studied using a small-signal model. This model is directly extracted from a look-up switching table and enables the stability analysis of concurrent variations in the system parameters. This work also shows that a decrease in the grid inductance does not necessarily improve the stability of grid connected converters as the system stability is a function of both grid inductance and impedance. Also, an increase in the filter inductance to improve the total harmonic distortion (THD) of grid current may deteriorate the system stability. Therefore, stability studies must be conducted upon the provision of such means for decreasing the THD. These findings are verified through extensive simulation.

Model-Free DPC of Grid Connected Converters Under the Weak Grid Condition Keywords:

Grid connected converters , weak grids , direct power control , small-signal model , state-space model , stability analysis