This paper presents an investigation on the effect of grid impedance variation on the control of grid connected voltage source converter when they are controlled using synchronous reference frame (SRF) current controllers in micro-grid applications. Mutual coupling terms introduced between the d and q control loops in SRF PI controller which are normally decoupled using the grid impedance through a feed-forward control to achieve independent control of active and reactive powers. But if the configurations change in systems like micro-grids due to intermittent nature of renewable energy sources then the feed forward decoupling becomes inadequate. A practical micro-grid and its parameters are taken for the investigation and the analysis is extended through simulation studies. The effectiveness of decoupling and the system stability under configuration change in micro-grids were investigated. The loss of independency of power control and stability analysis is presented to justify the need for a dynamic intelligent controller.
Dr. Vijayakumari A., Devarajan, A. T., and Devarajan, N., “Effect of Grid Impedance Variation on the Control of Grid Connected Converters with Synchronous Reference Frame Controllers in Micro-Grids”, in Power Electronics and Renewable Energy Systems, Lecture Notes on Electrical Engineering, New Delhi, 2014.