Measuring of earth fault current
View Patent ↗Method and apparatus for measuring an earth fault current in an output circuit of an inverter (INU) operating on the PWM principle and forming alternating-current voltage from direct-current voltage, the output currents (i U , i V and i W ) of which inverter are measured, and which inverter comprises at least two phase switches implemented with power semiconductor components (V 1 -V 6 , D 1 -D 6 ), which switches, controlled by a control unit, connect their own output phases to a positive (+) pole and to a negative (−) pole of a direct-current voltage source such that the phase switches are repeatedly both in different positions and also in the same positions, wherein the results of current measurement during two opposite switch position combinations are recorded in memory, and the earth fault current is calculated by forming a difference of the measurement results of said combinations.
1. Method for measuring an earth fault current in an output circuit of an inverter (INU) operating on the PWM principle and forming alternating-current voltage from direct-current voltage,
the output currents (i U , i V and i W ) of which inverter are measured, and
which inverter comprises at least two phase switches implemented with power semiconductor components (V 1 -V 6 , D 1 -D 6 ), which switches, controlled by a control unit, connect their own output phases to a positive (+) pole and to a negative (−) pole of a direct-current voltage source such that the phase switches are repeatedly both in different positions and also in the same positions,
characterized in that
in the method the results of current measurement during two opposite switch position combinations are recorded in memory, and
the earth fault current is calculated by forming a difference of the measurement results of said combinations.
2. Method according to claim 1 ,
characterized in that
the output current of the inverter is measured by means of a current sensor disposed in the DC intermediate circuit, and
the measurement results of current needed for calculating the earth fault current are recorded in memory when all the output phases are in the (+) position and when all the output phases are in the (−) position.
3. Method according to claim 2 ,
characterized in that
the value of an earth fault current is calculated to be half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.
4. Method according to claim 1 ,
characterized in that
the output current of the inverter is measured from each output phase with its own current sensors, and
the phase-specific measurement results of current are summed together, and
the measurement results of current from all the phases are recorded in memory when all the output phases are in the (+) position and when all the output phases are in the (−) position.
5. Method according to claim 4 ,
characterized in that
the value of an earth fault current is calculated to be half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.
6. Method according to claim 1 ,
characterized in that
the output current of the inverter is measured from each output phase with its own current sensors, and
the phase-specific measurement results of current are summed together, and
the measurement results of current from all the phases are recorded in memory when one output phase is in the (+) position and the other output phases are in the (−) position, and when the same output phase is in the (−) position and the other output phases are in the (+) position.
7. Method according to claim 6 ,
characterized in that
the value of an earth fault current is calculated to be half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.
8. Method according to claim 1 ,
characterized in that
the value of an earth fault current is calculated to be half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.
9. Apparatus for measuring an earth fault current in an output circuit of an inverter (INU) operating on the PWM principle and forming alternating-current voltage from direct-current voltage,
which apparatus comprises means for measuring the output currents (i U , i V and i W ) of an inverter, and
which inverter comprises at least two phase switches implemented with power semiconductor components (V 1 -V 6 , D 1 -D 6 ), which switches, controlled by a control unit, connect their own output phases to a positive (+) pole and to a negative (−) pole of a direct-current voltage source such that the phase switches are repeatedly both in different positions and also in the same positions,
characterized in that the apparatus is fitted
to record in memory the results of current measurement during two opposite switch position combinations, and
to calculate the earth fault current by forming a difference of the measurement results of said combinations.
10. Apparatus according to claim 9 ,
characterized in that
the output currents of the inverter are measured by means of a current sensor disposed in the DC intermediate circuit, and
the apparatus comprises a memory, in which case the measurement results of current needed for calculating the earth fault current are recorded in memory when all the output phases are in the (+) position and when all the output phases are in the (−) position.
11. Apparatus according to claim 10 ,
characterized in that the apparatus is fitted to calculate the value of an earth fault current such that it is half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.
12. Apparatus according to claim 9 ,
characterized in that
the output currents of the inverter are measured from each output phase with their own current sensors, and
the apparatus comprises means for summing together the phase-specific measurement results of current, and
the apparatus comprises a memory, in which case the measurement results of current from all the phases are recorded in memory when all the output phases are in the (+) position and when all the output phases are in the (−) position.
13. Apparatus according to claim 12 ,
characterized in that the apparatus is fitted to calculate the value of an earth fault current such that it is half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi N1 ) recorded in memory during opposite switch position combinations.
14. Apparatus according to claim 9 ,
characterized in that
the output currents of the inverter are measured from each output phase with their own current sensors, and
the apparatus comprises means for summing together the phase-specific measurement results of current, and
the apparatus comprises a memory, in which case the measurement results of current from all the phases are recorded in memory when one output phase is in the (+) position and the other output phases are in the (−) position, and when the same output phase is in the (−) position and the other output phases are in the (+) position.
15. Apparatus according to claim 14 ,
characterized in that the apparatus is fitted to calculate the value of an earth fault current such that it is half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.
16. Apparatus according to claim 9 ,
characterized in that the apparatus is fitted to calculate the value of an earth fault current such that it is half the difference of the measurement results (Δi DCP and Δi DCN , Δi P0 and Δi N0 , Δi P1 and Δi N1 ) recorded in memory during opposite switch position combinations.