Method, Electronic Device and System for Iteratively Measuring the Insulation Resistance of an Energized Electrical Apparatus With Respect to Ground

An electronic device for measuring a negative terminal insulation resistance (Rin), present between a negative terminal of an energized electrical apparatus and a ground ideally isolated from the energized electrical apparatus, and a positive terminal insulation resistance (Rip), present between a positive terminal of the energized electrical apparatus and said ground ideally isolated from the energized electrical apparatus, wherein the device comprises:

• a first device terminal and a second device terminal being connectable to the negative and positive terminals of the energized electrical apparatus, respectively;
• a first switching circuit arranged between said positive terminal and ground, thus in parallel with said positive terminal insulation resistance (Rip), wherein the first switching circuit comprises a first switching unit, configured to take either one of two states according to a driving signal having a positive branch switching duty-cycle (dp), and a first sample resistance (Rkp) arranged in series with respect to said first switching unit;
• a second switching circuit arranged between said negative terminal and ground, thus in parallel with said negative terminal insulation resistance (Rin), wherein the second switching circuit comprises a second switching unit configured to take either one of two states according to a driving signal having a negative branch switching duty-cycle (dn) and a second sample resistance (Rkn) arranged in series with respect to said second switching unit;
• an electronic control processor configured to:
• define at least two working points of the circuit consisting of the energized electrical apparatus, the first switching circuit, and the second switching circuit, wherein the first working point is associated with a first positive branch switching duty-cycle value (dp1) and a first negative branch switching duty-cycle value (dn1), and the second working point is associated with a second positive branch switching duty-cycle value (dp2) and a second negative branch switching duty-cycle value (dn2);
• control the first switching circuit and the second switching circuit so that they operate in accordance with said first working point, and measure, in such a condition, a respective first battery voltage value (VB1) present between said negative terminal and positive terminal and a respective first reference voltage value (Viso1) representative of a voltage present at the ends of one of the first switching circuit and the second switching circuit, determined by the first working point and also dependent on both the negative terminal insulation resistance (Rin) and the positive terminal insulation resistance (Rip);
• control the first switching circuit and the second switching circuit so that they operate in accordance with said second working point, and measure, in such a condition, a respective second battery voltage value (VB2) present between said negative terminal and positive terminal and a respective second reference voltage value (Viso2) representative of a voltage present at the ends of one of the first switching circuit and the second switching circuit, determined by the second working point and also dependent on both the negative terminal insulation resistance (Rin) and the positive terminal insulation resistance (Rip);
• calculate said negative terminal insulation resistance (Rin) and said positive terminal insulation resistance (Rip), based on said first battery voltage value (VB1), first reference voltage value (Viso1), second battery voltage value (VB2), and second reference voltage value (Viso2);
• wherein the electronic control processor is configured to determine said first positive branch switching duty-cycle value (dp1), first negative branch switching duty-cycle value (dn1), second positive branch switching duty-cycle value (dp2), and second negative branch switching duty-cycle value (dn2) based on the criterion of keeping the first reference voltage value (Viso1) and the second reference voltage value (Viso2) within a given neighborhood with respect to a predefined reference target voltage (Vt).

An electronic system for measuring a negative terminal insulation resistance (Rin), present between a negative terminal of an energized electrical apparatus and a ground ideally isolated from the energized electrical apparatus, and a positive terminal insulation resistance (Rip), present between a positive terminal of the energized electrical apparatus and said ground ideally isolated from the energized electrical apparatus, wherein the system comprises:

• an electronic device comprising a first device terminal and a second device terminal being connectable to the negative and positive terminals of the energized electrical apparatus, respectively, and further comprising:
• a first switching circuit, arranged between said positive terminal and ground, comprising a first switching unit, configured to take either one of two states according to a first driving signal having a positive branch switching duty-cycle (dp), and a first sample resistance (Rkp) arranged in series with respect to said first switching unit;
• a second switching circuit arranged between said negative terminal and ground, and comprising a second switching unit configured to take either one of two states according to a second driving signal having a negative branch switching duty-cycle (dn) and a second sample resistance (Rkn) arranged in series with respect to said second switching unit;
• at least one measurement circuit, configured to measure a battery voltage (VB) present between said negative terminal and positive terminal and a reference voltage (Viso) representative of a voltage present at the ends of one of the first switching circuit and the second switching circuit;
• an electronic control processor (C(s)) configured to:
• define at least two working points of the circuit consisting of the energized electrical apparatus, the first switching circuit, and the second switching circuit, wherein the first working point is associated with a first positive branch switching duty-cycle value (dp1) and a first negative branch switching duty-cycle value (dn1), and the second working point is associated with a second positive branch switching duty-cycle value (dp2) and a second negative branch switching duty-cycle value (dn2);
• control the first switching circuit and the second switching circuit so that they operate in accordance with said first working point, determining said first driving signal and said second driving signal based on the first working point defined, and providing the first switching circuit with said first driving signal and the second switching circuit with said second driving signal;
• control the first switching circuit and the second switching circuit so that they operate in accordance with said second working point, determining said first driving signal and said second driving signal based on the defined second working point, and providing the first switching circuit with said first driving signal and the second switching circuit with said second driving signal;
• receive from the at least one measurement circuit, in the condition in which the first switching circuit and the second switching circuit operate in accordance with the first working point, a respective first battery voltage value (VB1) measured between said negative terminal and positive terminal and a respective first reference voltage value (Viso1) representative of a voltage present at the ends of one of the first switching circuit and the second switching circuit;
• receive from the at least one measurement circuit, in the condition in which the first switching circuit and the second switching circuit operate in accordance with the second working point, a respective second battery voltage value (VB2) measured between said negative terminal and positive terminal and a respective second reference voltage value (Viso2) representative of a voltage present at the ends of one of the first switching circuit and the second switching circuit;
• calculate said negative terminal insulation resistance (Rin) and said positive terminal insulation resistance (Rip), based on said first battery voltage value (VB1), first reference voltage value (Viso1), second battery voltage value (VB2), and second reference voltage value (Viso2);
• wherein the electronic control processor is further configured to determine said first positive branch switching duty-cycle value (dp1), first negative branch switching duty-cycle value (dn1), second positive branch switching duty-cycle value (dp2), and second negative branch switching duty-cycle value (dn2) based on the criterion of keeping the first reference voltage value (Viso1) and the second reference voltage value (Viso2) within a given neighborhood with respect to a predefined reference target voltage (Vt).