A method For preventing saturation of a transformer during Fast voltage changes by correction of magnetic Flux of the transformer, said transformer having a primary winding with a power electronic converter and a secondary winding, by estimating or measuring a primary signal (i i), including a primary voltage on the primary winding of the transformer and optionally a primary current on the primary winding of the transformer, and injecting a correction signal including a correction voltage, into the primary winding of the transformer so as to prevent saturation of the transformer, said method comprising Following steps: a) Acknowledgement of the commanded change of converter voltage, to be applied to the primary winding of the transformer, including initial values of voltage angle, voltage parameters and voltage change parameters on the primary winding of the transformer as the primary signal (i i), b) Generating a reference signal including a reference voltage signal U* by a referencing unit, c) Inputting the reference voltage signal U* to a reference Flux trajectory calculator which - based thereon - calculates a reference Flux Φ *, d) Inputting a combination of the reference magnetic Flux Φ* and the estimated magnetic Flux to a Flux controller, which - based thereon - generates a correction term Δ U*, e) Generating the corrected reference signal, comprising a correction term, U**, wherein U**=U*+Δ U*, f) Inputting the corrected reference voltage signal U** and (optionally) load of the secondary winding of the transformer and its change in time, to a Flux estimator, which - based thereon - calculates an estimated Flux Φ, g) Injecting the correction signal through the power electronic converter into the primary winding of the transformer, characterized in that in addition the Following steps are performed by an auxiliary predictive control unit, which contains the reference mathematical model of the system: h) Initialization of the mathematical model of the system with the acquired initial values of voltage angle and voltage parameters, as well as the acquired or pre-configured voltage change parameters, i) Calculation of an expected magnetic Flux trajectory Φ̂( t) using the mathematical model of the system, j) Classifying the expected magnetic Flux trajectory Φ̂( t) so as to predict if saturation of the transformer is expected to happen by establishing its mean value, its maximal value Φ̂ max and its minimal value Φ̂ min and comparing them against a pre-determined magnetic core saturation limits ±Φ sat, k) Evaluating a Flux trajectory correction ΔΦ*( t) at which saturation would be avoided, or its occurrence would be minimized, l) Inputting the Flux trajectory correction ΔΦ*( t) into the Flux controller as an additional signal used by the Flux controller to generate the correction term Δ U*, wherein step g) is initialized with the same initial conditions which are used For the initialization of the mathematical model of the system in step h). a) Acknowledgement of the commanded change of converter voltage, to be applied to the primary winding of the transformer, including initial values of voltage angle, voltage parameters and voltage change parameters on the primary winding of the transformer as the primary signal (i i), b) Generating a reference signal including a reference voltage signal U* by a referencing unit, c) Inputting the reference voltage signal U* to a reference Flux trajectory calculator which - based thereon - calculates a reference Flux Φ *, d) Inputting a combination of the reference magnetic Flux Φ* and the estimated magnetic Flux to a Flux controller, which - based thereon - generates a correction term Δ U*, e) Generating the corrected reference signal, comprising a correction term, U**, wherein U**=U*+Δ U*, f) Inputting the corrected reference voltage signal U** and (optionally) load of the secondary winding of the transformer and its change in time, to a Flux estimator, which - based thereon - calculates an estimated Flux Φ, g) Injecting the correction signal through the power electronic converter into the primary winding of the transformer, h) Initialization of the mathematical model of the system with the acquired initial values of voltage angle and voltage parameters, as well as the acquired or pre-configured voltage change parameters, i) Calculation of an expected magnetic Flux trajectory Φ̂( t) using the mathematical model of the system, j) Classifying the expected magnetic Flux trajectory Φ̂( t) so as to predict if saturation of the transformer is expected to happen by establishing its mean value, its maximal value Φ̂ max and its minimal value Φ̂ min and comparing them against a pre-determined magnetic core saturation limits ±Φ sat, k) Evaluating a Flux trajectory correction ΔΦ*( t) at which saturation would be avoided, or its occurrence would be minimized, l) Inputting the Flux trajectory correction ΔΦ*( t) into the Flux controller as an additional signal used by the Flux controller to generate the correction term Δ U*, wherein step g) is initialized with the same initial conditions which are used For the initialization of the mathematical model of the system in step h).