Converter device for converting electric voltage levels (U/2, -U/2, UREF; U, UREF, U/2) available on a first, a second and a third voltage line of a first type (P, N, REF; PP, REF, P), into a voltage (VA; VC) on a voltage line of a second type (A; C), in either direction, the said device comprising: - a first main switching unit connected to the said first voltage line of the first type (P; PP) and equipped with a first main switch (K1; T1; T11, D11, T12, D12; T1, D1; D1), - a second main switching unit connected to the said second voltage line of the first type (N; REF) and equipped with a second main switch (K2; T2; T22, D22, T21, D21; T2, D2; D2), - a main switching point connected to the said voltage line of the second type (A; C) and connected to the said first and to the said second main switching unit, and - a third main switch (K3; T3; DP, T12, D12, DN, T21, D21; T31, D31, T32, D32; T31, D32; T32, D31) common to the said first and to the said second main switching unit, the said third main switch being connected between the said main switching point and the third voltage line of the first type (REF; P), characterized in that it comprises: - a first, a second and a third capacitor (CR1, CR2, CR3) connected between the said main switching point and, respectively, the said first, the said second and the said third voltage line of the first type, - a first auxiliary switching unit connected between the first voltage line of the first type, the second voltage line of the first type, and a first auxiliary switching point, - a second auxiliary switching unit connected between the first voltage line of the first type, the second voltage line of the first type, the third voltage line of the first type and a second auxiliary switching point, and - a transformer equipped with windings (N1, N2) provided with two free ends and with two ends connected to a common point, the said common point being connected to the said main switching point, the two free ends being respectively connected to the said first auxiliary switching point and the said second auxiliary switching point. - a first main switching unit connected to the said first voltage line of the first type (P; PP) and equipped with a first main switch (K1; T1; T11, D11, T12, D12; T1, D1; D1), - a second main switching unit connected to the said second voltage line of the first type (N; REF) and equipped with a second main switch (K2; T2; T22, D22, T21, D21; T2, D2; D2), - a main switching point connected to the said voltage line of the second type (A; C) and connected to the said first and to the said second main switching unit, and - a third main switch (K3; T3; DP, T12, D12, DN, T21, D21; T31, D31, T32, D32; T31, D32; T32, D31) common to the said first and to the said second main switching unit, the said third main switch being connected between the said main switching point and the third voltage line of the first type (REF; P), - a first, a second and a third capacitor (CR1, CR2, CR3) connected between the said main switching point and, respectively, the said first, the said second and the said third voltage line of the first type, - a first auxiliary switching unit connected between the first voltage line of the first type, the second voltage line of the first type, and a first auxiliary switching point, - a second auxiliary switching unit connected between the first voltage line of the first type, the second voltage line of the first type, the third voltage line of the first type and a second auxiliary switching point, and - a transformer equipped with windings (N1, N2) provided with two free ends and with two ends connected to a common point, the said common point being connected to the said main switching point, the two free ends being respectively connected to the said first auxiliary switching point and the said second auxiliary switching point.