Method for operating an electrical converter that has an at least two-phase AC voltage side having at least two AC voltage connections (W1, W2, W3), a DC voltage side and at least two parallel-connected series circuits (RES1, RES2, RES3), - wherein each of the series circuits (RES1, RES2, RES3) in each case forms a converter arm of the converter and is assigned to one of the AC voltage connections (W1, W2, W3) on the AC voltage side of the converter and - wherein one or more circuit currents are able to flow between the at least two parallel-connected series circuits (RES1, RES2, RES3), wherein - a loading value describing the thermal loading of the converter is calculated on the basis of at least three current values, specifically - an active power current value that indicates the active power current component of a phase current flowing through one of the AC voltage connections (W1, W2, W3), - a reactive power current value that indicates the reactive power current component of the phase current flowing through the abovementioned AC voltage connection (W1, W2, W3), and - a circuit current value that indicates the magnitude of the one or more circuit currents flowing between the series circuits (RES1, RES2, RES3), and - the converter is controlled at least also taking into consideration this loading value, characterized in that the temporally changing loading value is ascertained in accordance with Ith = 1 a ⋅ Ip 2 + Iq 2 + k 1 ⋅ Ip ⋅ ƒ Vconv Vdc + k 2 ⋅ Ik wherein - Ip denotes the abovementioned active power current value and is formed by the absolute value or the amplitude of the active power current component of the phase current flowing through the AC voltage connection (W1, W2, W3), - Iq denotes the abovementioned reactive power current value and is formed by the absolute value or the amplitude of the reactive power current component of the phase current flowing through the AC voltage connection (W1, W2, W3), - Vconv denotes the absolute value or the amplitude of the voltage at the AC voltage connection (W1, W2, W3), - Vdc denotes the absolute value or the amplitude of the DC voltage on the DC voltage side, - ƒ Vconv Vdc denotes a predefined function of a quotient formed from the absolute value or the amplitude of the voltage at the AC voltage connection (W1, W2, W3) and the DC voltage on the DC voltage side, - Ik denotes the circuit current value and is formed by the absolute value or the amplitude of the greatest series circuit-related circuit current, and - a, k1 and k2 are predefined constants. - wherein each of the series circuits (RES1, RES2, RES3) in each case forms a converter arm of the converter and is assigned to one of the AC voltage connections (W1, W2, W3) on the AC voltage side of the converter and - wherein one or more circuit currents are able to flow between the at least two parallel-connected series circuits (RES1, RES2, RES3), wherein - a loading value describing the thermal loading of the converter is calculated on the basis of at least three current values, specifically - an active power current value that indicates the active power current component of a phase current flowing through one of the AC voltage connections (W1, W2, W3), - a reactive power current value that indicates the reactive power current component of the phase current flowing through the abovementioned AC voltage connection (W1, W2, W3), and - a circuit current value that indicates the magnitude of the one or more circuit currents flowing between the series circuits (RES1, RES2, RES3), and - the converter is controlled at least also taking into consideration this loading value, - Ip denotes the abovementioned active power current value and is formed by the absolute value or the amplitude of the active power current component of the phase current flowing through the AC voltage connection (W1, W2, W3), - Iq denotes the abovementioned reactive power current value and is formed by the absolute value or the amplitude of the reactive power current component of the phase current flowing through the AC voltage connection (W1, W2, W3), - Vconv denotes the absolute value or the amplitude of the voltage at the AC voltage connection (W1, W2, W3), - Vdc denotes the absolute value or the amplitude of the DC voltage on the DC voltage side, - ƒ Vconv Vdc denotes a predefined function of a quotient formed from the absolute value or the amplitude of the voltage at the AC voltage connection (W1, W2, W3) and the DC voltage on the DC voltage side, - Ik denotes the circuit current value and is formed by the absolute value or the amplitude of the greatest series circuit-related circuit current, and - a, k1 and k2 are predefined constants.