Control method for voltage source converters in systems with high frequency variability

In recent years there has been much attention on the proportional plus resonant (P-R) current regulators for grid connected voltage-source converters (VSCs). Many strategies have been proposed for use of P-R controllers both in the stationary and in the synchronous reference frame that demonstrate VSC performance can be improved under non-ideal supply conditions such as supply asymmetry and supply voltage distortion. However, when employed in systems with high frequency variability such as micro-grids, the phase-locked loop (PLL) required for operation in the synchronous reference frame or for dynamic retuning of the resonant controller may experience poor performance or even loss of phase-lock. A method is presented here based on current decomposition that uses an efficient RDFT algorithm to compute equivalent admittances and allows control of grid connected VSCs to be performed in the stationary reference frame without supply synchronization. While only slightly more computationally burdensome, the method provides better performance in systems with high frequency variability. In this paper the proposed method is described and then performance is evaluated for systems with high frequency variability such as micro-grids with large step or pulsed loads.