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 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 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 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 delivered to the load so that ε 3 =0, that is P=P n. ∘ the power 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 delivered to the load so that ε 3 =0, that is P=P n.