Patent ID: 9337645
Filing Date: 2016-05-10
CPC Classification: H02H,H02M

Claim Text:
1. A method in a controller for protection of a voltage source converter comprising three phases connected in delta connection, each phase comprising two or more series-connected converter cells and a respective phase reactor, each converter cell comprising a half-bridge converter cell or a full converter cell, further each converter cell having a by-pass switch connected in parallel with the respective converter cell for enabling by-pass thereof, the method comprising the steps of: detecting an over-voltage condition, wherein the step of detecting the over-voltage condition comprises measuring an AC voltage of a power grid to which the voltage source converter is connected and determining this AC voltage to exceed a maximum operation voltage of the voltage source converter, and/or measuring a DC voltage of the one or more converter cells and determining this DC voltage to exceed a preset value, and/or measuring a current in the one or more phases and determining this current to exceed a preset value, and controlling simultaneously the by-pass switches of each converter cell to be configured in closed position so as to short-circuit the converter cells and by-pass the converter cells upon detection of the over-voltage condition, wherein the voltage source converter enters a passive mode upon the converter cells being by-passed, in which in the passive mode the respective phase reactor of each of the three phases absorbs inductive overcurrent caused by the detected overvoltage condition.