METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE WITH AN EXHAUST-GAS TURBOCHARGER HAVING VARIABLE TURBINE GEOMETRY TAKING INTO CONSIDERATION THE EXHAUST-GAS BACK PRESSURE

The invention relates to a method for operating an internal combustion engine (100) having an exhaust-gas turbocharger (5, 10, 15) for compressing the air fed to the internal combustion engine (100), wherein a drive power of a turbine (10) of the exhaust-gas turbocharger (5, 10, 15) in an exhaust tract (20) of the internal combustion engine (100) is changed through variation of a turbine geometry of the turbine (10), wherein, in a first control algorithm (I), a setpoint charge pressure (pLSoll) at the outlet of the compressor (5) of the exhaust-gas turbocharger (5, 10, 15) in the air feed tract (50) upstream of the combustion motor (55) is controlled in a manner dependent on a setpoint exhaust-gas back pressure (pT1Soll) to be set in an exhaust tract (20) downstream of the combustion motor (55) upstream of the turbine (10) of the internal combustion engine (100), wherein the setpoint charge pressure (pLSoll) is assigned an opening cross-sectional area of the turbine (10), which is controlled, by means of an actuating stroke of an actuating element (25) assigned to the turbine (10), in a manner dependent on a setpoint value (25Soll) assigned to the predefined setpoint charge pressure (pLSoll). According to the invention, provision is made for the actuating element (25), which is actuated by means of the first control algorithm (I), of the turbine (10) to be controlled by means of a second control algorithm (II), with predefinition of an upper threshold value of the setpoint exhaust-gas back pressure (pT1Soll) in the exhaust tract (20) upstream of the turbine (10) by intervention into the first control algorithm (I) with an adapted setpoint value (25′Soll), if, in a primary control path a) of the second control algorithm (II), a control deviation (ΔpT) upstream of the turbine (10) arises which is formed from an actual exhaust-gas back pressure (pT1lst) upstream of the turbine (10) and the predefined setpoint exhaust-gas back pressure (pT1Soll) upstream of the turbine (10), and, in a secondary control path b) of the second control algorithm (II), a control deviation (ΔpL) downstream of the compressor (5) arises which is formed from an actual charge pressure (pLlst) of the compressor (5) and the setpoint charge pressure (pLSoll) at the outlet of the compressor (5).