A method for controlling a head of an induction machine for heating a load, equipped with a bridge inverter and capacitor, for determining an operating resonance frequency (F 0 ) in a frequency range between a minimum frequency (F min ) and a maximum frequency (F max ) as a function of an operating nominal power (P n ), characterised by comprising the following steps of: • Setting a start frequency (F start ) to an intermediate value between said minimum and maximum frequencies (F min , F max ) and a start power (P min ) equal to a fraction of said nominal power (P n ), for the initial start-up of the machine; • Increasing the operating power by bringing it from the start power (P min ) to an intermediate power (Pmid) equal to about 50% of said nominal power (P n ); • Applying a first control loop wherein: ∘ a load current I loαd and a capacitor current I c are measured to calculate a first error parameter (ε 1 ): ε 1 = I load → 2 − I c → 2 ; e ∘ the working frequency is changed, by determining an approximate frequency value (F 0app ) so that ε 1 = 0; • Applying a second control loop wherein: ∘ a bridge current I L is measured to calculate a second error parameter (ε 2 ): ε 2 = I load → 2 − I c → 2 + I L → 2 ; ∘ the working frequency is changed, by determining a frequency value so that ε 2 = 0, by considering this value as resonance frequency (F 0 ); • Applying a third control loop wherein: ∘ the power (P) delivered to the load is measured to calculate a third error parameter (ε 3 ): ε 3 = P − P n ; ∘ the working power is changed, by determining a power (P) delivered to the load so that ε 3 =0, that is P=P n . • Setting a start frequency (F start ) to an intermediate value between said minimum and maximum frequencies (F min , F max ) and a start power (P min ) equal to a fraction of said nominal power (P n ), for the initial start-up of the machine; • Increasing the operating power by bringing it from the start power (P min ) to an intermediate power (Pmid) equal to about 50% of said nominal power (P n ); • Applying a first control loop wherein: ∘ a load current I loαd and a capacitor current I c are measured to calculate a first error parameter (ε 1 ): ε 1 = I load → 2 − I c → 2 ; e ∘ the working frequency is changed, by determining an approximate frequency value (F 0app ) so that ε 1 = 0; ∘ a load current I loαd and a capacitor current I c are measured to calculate a first error parameter (ε 1 ): ε 1 = I load → 2 − I c → 2 ; e ∘ the working frequency is changed, by determining an approximate frequency value (F 0app ) so that ε 1 = 0; • Applying a second control loop wherein: ∘ a bridge current I L is measured to calculate a second error parameter (ε 2 ): ε 2 = I load → 2 − I c → 2 + I L → 2 ; ∘ the working frequency is changed, by determining a frequency value so that ε 2 = 0, by considering this value as resonance frequency (F 0 ); ∘ a bridge current I L is measured to calculate a second error parameter (ε 2 ): ε 2 = I load → 2 − I c → 2 + I L → 2 ; ∘ the working frequency is changed, by determining a frequency value so that ε 2 = 0, by considering this value as resonance frequency (F 0 ); • Applying a third control loop wherein: ∘ the power (P) delivered to the load is measured to calculate a third error parameter (ε 3 ): ε 3 = P − P n ; ∘ the working power is changed, by determining a power (P) delivered to the load so that ε 3 =0, that is P=P n . ∘ the power (P) delivered to the load is measured to calculate a third error parameter (ε 3 ): ε 3 = P − P n ; ∘ the working power is changed, by determining a power (P) delivered to the load so that ε 3 =0, that is P=P n . <EOS>