An electronic power converter, suitable, in a first mode, for receiving electrical voltage and/or current quantities from a first device as input, for processing them using processing means (10, 12) capable of measuring said electrical quantities and servocontrolling said electrical quantities based on said measurements and constraints specific to a second device, and for providing the adapted voltage and/or current quantities to said second device, the electronic power converter further comprising means for determining the impedance of the energy source at a given frequency, based on intensity and voltage values measured across the terminals of the energy source, said electric converter being characterized in that: the power converter is suitable for, in a first state of a second mode of the converter, when one of the first and second devices is an electricity source, imposing a direct current having a predetermined value (I 0) across the terminals of said energy source; the power converter is further suitable for measuring current and voltage values across the terminals of the energy source during said first state of the second mode, for determining, as a function of said measured current values, a current offset value and, as a function of said measured voltage values, a voltage offset value, said current and voltage offset values being further function of an operating range of the processing means; the power converter is suitable for exciting, in a second state of the second mode, the energy source by injecting alternating current at least at one fixed excitation frequency, said alternating current being superimposed on the determined imposed direct current; and wherein the processing means are suitable, in the second state of the second mode, for measuring successive current and voltage values (Ialt-out, Valt-out) across the terminals of the energy source following the excitation at said excitation frequency, after offsetting said current values, voltage values, respectively, as a function of said determined current offset value, said determined voltage offset value, respectively; said means for determining the impedance of the energy source being suitable for determining the impedance of the energy source at the fixed excitation frequency, based on said intensity and voltage values measured successively. the power converter is suitable for, in a first state of a second mode of the converter, when one of the first and second devices is an electricity source, imposing a direct current having a predetermined value (I 0) across the terminals of said energy source; the power converter is further suitable for measuring current and voltage values across the terminals of the energy source during said first state of the second mode, for determining, as a function of said measured current values, a current offset value and, as a function of said measured voltage values, a voltage offset value, said current and voltage offset values being further function of an operating range of the processing means; the power converter is suitable for exciting, in a second state of the second mode, the energy source by injecting alternating current at least at one fixed excitation frequency, said alternating current being superimposed on the determined imposed direct current; and wherein the processing means are suitable, in the second state of the second mode, for measuring successive current and voltage values (Ialt-out, Valt-out) across the terminals of the energy source following the excitation at said excitation frequency, after offsetting said current values, voltage values, respectively, as a function of said determined current offset value, said determined voltage offset value, respectively; said means for determining the impedance of the energy source being suitable for determining the impedance of the energy source at the fixed excitation frequency, based on said intensity and voltage values measured successively.