Converter protecting components against overvoltages
View Patent ↗A converter includes a converter bridge ( 101 ) adapted to transfer electrical energy between the AC terminal ( 102 ) and the DC terminal ( 103 ) of the converter. The converter also includes electrical paths bypassing the converter bridge for conducting overvoltage transients occurring in the AC terminal around the converter bridge to the DC terminal. Each electrical path includes a unidirectionally conductive semiconductor component ( 104 a, 104 b, 104 c ), such as a diode, and a voltage-limiting component ( 105 ) for which the ratio of voltage change to current change is small when the voltage of the voltage-limiting component is greater than a predetermined threshold voltage. Because of the overvoltage protection thus achieved, AC chokes can be omitted from the AC terminal or at least they can be designed smaller, reducing the load-dependent voltage drop of the DC terminal.
1. A converter, comprising:
a converter bridge configured to transfer electrical energy between an AC terminal and a DC terminal of the converter;
at least one capacitor on an electrical path from a first pole of the DC terminal to a second pole of the DC terminal; and
electrical paths for conducting overvoltage transients occurring in said AC terminal into said DC terminal in order to absorb the overvoltage transients into the at least one capacitor, the electrical paths being located between each of the phases of the AC terminal and the first pole of the DC terminal, each electrical path comprising:
a unidirectionally conductive semiconductor component, and
a voltage-limiting component in which the ratio of voltage to current is greater than a predetermined value in response to a situation in which the voltage across the voltage-limiting component is smaller than a predetermined threshold voltage, and in which the ratio of voltage change to current change is smaller than said predetermined value in response to a situation in which the voltage across the voltage-limiting component is greater than said threshold voltage, the predetermined threshold voltage being greater than a voltage between one of the phases of the AC terminal and the first pole of the DC terminal when current flows, via the converter bridge, between the one of the phases of the AC terminal and the first pole of the DC terminal so as to allow the converter bridge to determine a voltage of the DC terminal.
2. The converter according to claim 1 , wherein the voltage-limiting component on each of the electrical paths is common to said electrical paths and a first pole of the voltage-limiting component is connected to said first pole of the DC terminal, and
a second pole of the voltage-limiting component is connected with the unidirectionally conductive semiconductor components of the electrical paths, said semiconductor components being connected mutually in the same direction.
3. The converter according to claim 2 , wherein one pole of the voltage-limiting component is connected to the first pole of the DC terminal via a switch.
4. The converter according to claim 3 , further comprising a resistor configured to supply energy from said AC terminal to said DC terminal via said unidirectionally conductive semiconductor components, the resistor being in parallel with a series connection comprised of the voltage-limiting component and the switch.
5. The converter according to claim 2 , further comprising a second voltage-limiting component between the first pole of said voltage-limiting component and the second pole of said DC terminal.
6. The converter according to claim 1 , wherein said first pole of the DC terminal is the positive pole of the DC terminal and each unidirectionally conductive semiconductor component is adapted to conduct electric current towards said positive pole of the DC terminal.
7. The converter according to claim 6 , wherein said converter bridge comprises:
thyristors between the phases of the AC terminal and the positive pole of the DC terminal, and
diodes between the negative pole of the DC terminal and the phases of the AC terminal.
8. The converter according to claim 1 , wherein said first pole of the DC terminal is the negative pole of the DC terminal and each unidirectionally conductive semiconductor component is adapted to conduct electric current towards the AC terminal.
9. The converter according to claim 8 , wherein said converter bridge comprises:
diodes between the phases of the AC terminal and the positive pole of the DC terminal, and
thyristors between the negative pole of the DC terminal and the phases of the AC terminal.
10. The converter according to claim 1 , wherein the unidirectionally conductive semiconductor component is a diode.
11. The converter according to claim 1 , wherein the voltage-limiting component is one of a varistor, and a transient voltage suppressor (TVS).
12. The converter according to claim 1 , wherein the electrical paths bypass the converter bridge to conduct the overvoltage transients occurring in the AC terminal around the converter bridge to the at least one capacitor.
13. A method for protecting semiconductor components in a converter bridge against overvoltages, the converter bridge being configured to transfer electrical energy between an AC terminal and a DC terminal of a converter, the method comprising:
conducting overvoltage transients occurring in said AC terminal into said DC terminal via electrical paths provided between each of the phases of said AC terminal and a first pole of the DC terminal in order to absorb the overvoltage transients into at least one capacitor on an electrical path from the first pole of the DC terminal to a second pole of the DC terminal, each electrical path comprising a unidirectionally conductive semiconductor component and a voltage-limiting component in which the ratio of voltage to current is greater than a predetermined value in response to a situation in which the voltage across the voltage-limiting component is smaller than a predetermined threshold voltage, and in which the ratio of voltage change to current change is smaller than said predetermined value in response to a situation in which the voltage across the voltage-limiting component is greater than said threshold voltage, the predetermined threshold voltage being greater than a voltage between one of the phases of the AC terminal and the first pole of the DC terminal when current flows, via the converter bridge, between the one of the phases of the AC terminal and the first pole of the DC terminal so as to allow the converter bridge to determine a voltage of the DC terminal.
14. The method according to claim 13 , wherein the voltage-limiting component on each of the electrical paths is common to said electrical paths, and a first pole of the voltage-limiting component is connected to said first pole of the DC terminal, and a second pole of the voltage-limiting component is connected with the unidirectionally conductive semiconductor components of the electrical paths, said semiconductor components being connected mutually in the same direction.
15. The method according to claim 14 , wherein a reverse voltage in the semiconductor components of said converter bridge is limited by another voltage-limiting component located between a first pole of said voltage-limiting component and the second pole of said DC terminal.
16. The method according to claim 13 , wherein said first pole of the DC terminal is the positive pole of the DC terminal and each unidirectionally conductive semiconductor component is adapted to conduct electric current towards the positive pole of the DC terminal.
17. The method according to claim 13 , wherein said first pole of the DC terminal is the negative pole of the DC terminal and each unidirectionally conductive semiconductor component is adapted to conduct electric current towards the AC terminal.
18. The method according to claim 13 , wherein the unidirectionally conductive semiconductor component is a diode.
19. A method according to claim 13 , wherein the voltage-limiting component is one of a varistor and a transient voltage suppressor (TVS).
20. The method according to claim 13 , wherein the overvoltage transients are conducted via the electrical paths around the converter bridge to the at least one capacitor.