A method of thermal monitoring of a power device comprising an enclosure around a heat-generating component in contact with a circulating electrically insulating cooling fluid , the power device comprising a first sensor performing measurements relating to power losses of the power device and a second sensor performing measurements of a reference temperature of the power device, the method comprising: in a first computer processing environment (A), executing (S1) a first algorithm based on design information about the power device for at least two different operation states of the power device; from the first algorithm, deriving (S2) coefficients relating to heat transfer in the power device for the at least two different operation states; storing (S3) the derived coefficients in a database ; connecting (S4) the database to a second computer processing environment (B); during operation of the power device , the second computer processing environment (B) receiving (S5) information about the measurements performed by the first sensor and the second sensor ; and in the second computer processing environment (B), executing (S6) a second algorithm based on the stored coefficients and on the received measurement information for estimating at least one temperature of the heat generating component in the power device in real time; wherein, in contrast to the execution of the first algorithm, the second algorithm is executed continuously and automatically during operation of the power device ; the method being characterized by controlling (S7) the power device based on the estimated at least one temperature; wherein the different operation states are defined by different current loads (I) which give different fluid flow rates unless there is forced circulation of the cooling fluid. in a first computer processing environment (A), executing (S1) a first algorithm based on design information about the power device for at least two different operation states of the power device; from the first algorithm, deriving (S2) coefficients relating to heat transfer in the power device for the at least two different operation states; storing (S3) the derived coefficients in a database ; connecting (S4) the database to a second computer processing environment (B); during operation of the power device , the second computer processing environment (B) receiving (S5) information about the measurements performed by the first sensor and the second sensor ; and in the second computer processing environment (B), executing (S6) a second algorithm based on the stored coefficients and on the received measurement information for estimating at least one temperature of the heat generating component in the power device in real time; wherein, in contrast to the execution of the first algorithm, the second algorithm is executed continuously and automatically during operation of the power device ; the method being characterized by controlling (S7) the power device based on the estimated at least one temperature; wherein the different operation states are defined by different current loads (I) which give different fluid flow rates unless there is forced circulation of the cooling fluid. <EOS>