Patent ID: 9000734
Filing Date: 2015-04-07
Classification: H02J,H02M,H02P,Y02E

Abstract:
1. Method of operating a converter of a wind turbine for providing electric energy to a utility grid, the method comprising: determining a grid voltage; performing a first procedure including lowering the grid voltage if the grid voltage is between a nominal voltage and a first voltage threshold, the first voltage threshold being greater than the nominal voltage; performing a second procedure if the grid voltage is above the first voltage threshold, wherein the second procedure includes keeping a DC voltage of a converter in a specific range, wherein the first and second procedure are different, wherein the second procedure comprises, after enabling a chopper, disabling a pulse width modulation, wherein disabling the pulse width modulation comprises: switching a second controllable switch of a grid side converter portion to a non-conducting state, dissipating electric energy by current flow through a diode, wherein the second controllable switch and the diode are connected in parallel between two DC-nodes of a DC-link of the converter, wherein the second controllable switch is provided with pulse width modulation signals for controlling a conductance state of the second controllable switch to change with a higher frequency than the grid frequency, if the grid voltage deviates from the nominal voltage by less than a predefined percentage.