A method of controlling a gas turbine power plant including a gas turbine engine , and an electric power generator mechanically connected to the gas turbine engine , the gas turbine engine comprising a compressor , a combustor assembly and a turbine ; the method comprising determining at least one of a fuel supply and an air supply to the combustor assembly to control at least one of a load (P E ) and an exhaust temperature (T E ) of the gas turbine engine in accordance with a sliding-mode control technique; the method being further characterized in that controlling comprises determining a sliding quantity (S; S L ; S TE ), as a function of a control error between a current value and a reference value of a controlled variable, the controlled variable including at least one of a load (P E ) and an exhaust temperature (T E ) of the gas turbine engine , and determining a control law (U(S, t); U L (S L , t); U TE (S TE , t)), having a gain factor (k(S, t); k L (S L , t) ; k TE (S TE , t)) and a sliding factor (SF(S, t); SF L (S L , t); SF TE (S TE , t)) and configured to bring the sliding quantity (S; S L ; S TE ) on a sliding manifold (S') defined by states that cause the sliding quantity (S; S L ; S TE ) to be zero; the sliding factor (SF(S, t); SF L (S L , t); SF TE (S TE , t)) is a first function of the sliding quantity (S; S L ; S TE ) and a time derivative ( k̇ ( S,t ); k̇ ( S L , t ); k̇ ( S TE ,t )) of the gain factor (k(S, t); k L (S L , t); k TE (S TE , t)) is a second function of the sliding quantity (S; S L ; S TE ; and the time derivative ( k̇ ( S , t ); k̇ ( S L , t ); k̇ ( S TE ,t )) of the gain factor (k(S, t); k L (S L , t); k TE (S TE , t)) is negative in a first region (B 1 ) around the sliding manifold (S'), is zero in a second region (B 2 ) that surrounds the first region (B 1 ) and is positive in a third region (B 3 ) that surrounds the second region (B 2 ). the method comprising determining at least one of a fuel supply and an air supply to the combustor assembly to control at least one of a load (P E ) and an exhaust temperature (T E ) of the gas turbine engine in accordance with a sliding-mode control technique; the method being further characterized in that controlling comprises determining a sliding quantity (S; S L ; S TE ), as a function of a control error between a current value and a reference value of a controlled variable, the controlled variable including at least one of a load (P E ) and an exhaust temperature (T E ) of the gas turbine engine , and determining a control law (U(S, t); U L (S L , t); U TE (S TE , t)), having a gain factor (k(S, t); k L (S L , t) ; k TE (S TE , t)) and a sliding factor (SF(S, t); SF L (S L , t); SF TE (S TE , t)) and configured to bring the sliding quantity (S; S L ; S TE ) on a sliding manifold (S') defined by states that cause the sliding quantity (S; S L ; S TE ) to be zero; the sliding factor (SF(S, t); SF L (S L , t); SF TE (S TE , t)) is a first function of the sliding quantity (S; S L ; S TE ) and a time derivative ( k̇ ( S,t ); k̇ ( S L , t ); k̇ ( S TE ,t )) of the gain factor (k(S, t); k L (S L , t); k TE (S TE , t)) is a second function of the sliding quantity (S; S L ; S TE ; and the time derivative ( k̇ ( S , t ); k̇ ( S L , t ); k̇ ( S TE ,t )) of the gain factor (k(S, t); k L (S L , t); k TE (S TE , t)) is negative in a first region (B 1 ) around the sliding manifold (S'), is zero in a second region (B 2 ) that surrounds the first region (B 1 ) and is positive in a third region (B 3 ) that surrounds the second region (B 2 ). <EOS>