Bi-directional DC-DC resonant converter with bi-directional voltage control, comprising: - primary converter terminals (TCal, TCa2) defining a primary voltage; - secondary converter terminals (TCbl, TCb2) defining a secondary voltage; - a transformer device having primary transformer terminals (Tal, Ta2) and secondary transformer terminals (Tb1, Tb2); - a resonant tank device having first and second primary resonant tank terminals (a1, a2) defining a primary resonant tank voltage (Ua) and first and second secondary resonant tank terminals (b1, b2) defining a secondary resonant tank voltage (Ub), where the primary tank terminals (a1, a2) are connected to the secondary transformer terminals (Tb1, Tb2); - a primary switching circuit connected between the primary converter terminals (TCal, TCa2) and the primary transformer terminals (Tal, Ta2); - a secondary switching circuit connected between the secondary resonant tank terminals (b1, b2) and the secondary converter terminals (TCbl, TCb2); where the resonant tank device comprises a configuration switch for configuration of the converter between a first state, in which power is transferred from the secondary converter terminals (TCbl, TCb2) to the primary converter terminals (TCal, TCa2), and a second state, in which power is transferred from the primary converter terminals (TCal, TCa2) to the secondary converter terminals (TCbl, TCb2); where the resonant tank device comprises a resonant inductor (Lr), a magnetizing inductor (Lm) and a resonant capacitor (Cr; Cr1, Cr2) connected to the configuration switch; where a first gain (Gres1) is defined as the ratio between a first harmonic approximation (Ub_FHA) of the secondary resonant tank voltage (Ub) and a first harmonic approximation (Ua_FHA) of the primary resonant tank voltage (Ua) when operating at a first series resonance frequency (ω res1) in the first state; where a second gain (Gres2) is defined as the ratio between a first harmonic approximation (Ub_FHA) of the secondary resonant tank voltage (Ub) and a first harmonic approximation (Ua_FHA) of the primary resonant tank voltage (Ua) when operating at a second series resonance frequency (ω res2) in the second state; where the first gain (Gres1) is different from the second gain (Gres2); characterized in that: the first gain (Gres1) is equal to 1 when operating at the first series resonance frequency (ω res1) in the first state and where the second gain (Gres2) is determined by the inductance of the resonant inductor (Lr) and inductance of the magnetizing inductor (Lm) so that the second gain (Gres2) is equal to the sum of the inductance of the resonant inductor (Lr) and the inductance of the magnetizing inductor (Lm) divided on the inductance of the magnetizing inductor (Lm) when operating at the second series resonance frequency (ω res2) in the second state. - primary converter terminals (TCal, TCa2) defining a primary voltage; - secondary converter terminals (TCbl, TCb2) defining a secondary voltage; - a transformer device having primary transformer terminals (Tal, Ta2) and secondary transformer terminals (Tb1, Tb2); - a resonant tank device having first and second primary resonant tank terminals (a1, a2) defining a primary resonant tank voltage (Ua) and first and second secondary resonant tank terminals (b1, b2) defining a secondary resonant tank voltage (Ub), where the primary tank terminals (a1, a2) are connected to the secondary transformer terminals (Tb1, Tb2); - a primary switching circuit connected between the primary converter terminals (TCal, TCa2) and the primary transformer terminals (Tal, Ta2); - a secondary switching circuit connected between the secondary resonant tank terminals (b1, b2) and the secondary converter terminals (TCbl, TCb2); the first gain (Gres1) is equal to 1 when operating at the first series resonance frequency (ω res1) in the first state and where the second gain (Gres2) is determined by the inductance of the resonant inductor (Lr) and inductance of the magnetizing inductor (Lm) so that the second gain (Gres2) is equal to the sum of the inductance of the resonant inductor (Lr) and the inductance of the magnetizing inductor (Lm) divided on the inductance of the magnetizing inductor (Lm) when operating at the second series resonance frequency (ω res2) in the second state.