Method for fixing an output power limit of a frequency converter and a method for diagnosing conditions of DC-link capacitors
A method for fixing an output power limit of a frequency converter includes determining voltage differences between two DC-link circuit capacitors for each of two different values of an output power of a frequency converter; determining a percentile value for each voltage difference by rejecting values higher than the determined percentile. A method also includes comparing a value of an output power limit P outlimit of a frequency converter which is fixed; assessing conditions of the DC-link capacitors, wherein when the value of the nominal power P n is higher than the fixed output power limit P outlimit the frequency converter is used conditionally with the power P i lower than the fixed output power limit P outlimit without replacement of the at least two DC-link capacitors or at least two blocks of DC-link capacitors, where i=(1, 2 . . . , n).
1. A computer-implemented method for fixing an output power limit of a frequency converter, comprising:
determining voltage differences ΔU i between at least two DC-link circuit capacitors or at least two blocks of DC-link circuit capacitors for each of at least two different values of an output power P out (i) of a frequency converter, thus providing at least two sets of the voltage differences ΔU i , where i=(1, 2 . . . , n), wherein the voltage differences ΔU i are determined during stable thermal conditions of the frequency converter;
determining a percentile value for each set of the voltage differences ΔU i in order to eliminate the highest errors occurring during determination of voltage differences ΔU i , wherein the elimination is done through rejection of values higher than the determined percentile, where i=(1, 2 . . . , n);
determining characteristic ΔU=f(P out ) from the values of the percentile,
determining a maximum allowable voltage difference ΔU maxallow , where
Δ U maxallow =⅓ ·U dc
where U dc represents a voltage of a DC-link circuit;
fixing a value of an output power limit P outlimit of the frequency converter for the determined maximum allowable voltage difference ΔU maxallow .
2. The computer-implemented method according to claim 1 , wherein the output power limit P outlimit is fixed with a margin of an error factor F me , wherein 0<F me <1.
3. The computer-implemented method according to claim 2 , wherein the margin of the error factor F me is 0.9.
4. The computer-implemented method according to claim 1 , wherein determining voltage differences ΔU i comprises determining at least 100 samples of the voltage differences ΔU i .
5. The computer-implemented method according to claim 1 , wherein the percentile is of at least 75th.
6. The computer-implemented method according to claim 5 , wherein the percentile is of 98th.
7. The computer-implemented method according to claim 1 , wherein the DC link circuit capacitors are electrolytic capacitors.
8. A computer-implemented method for diagnosing conditions of DC-link capacitors, comprising:
comparing a value of an output power limit P outlimit of a frequency converter comprising at least two DC-link capacitors or at least two blocks of DC-link capacitors with a value of a nominal power P n of the frequency converter, wherein the value of the output power limit P outlimit is fixed by:
determining voltage differences ΔU i between at least two DC-link circuit capacitors or at least two blocks of DC-link circuit capacitors for each of at least two different values of an output power P out (i) of a frequency converter, thus providing at least two sets of the voltage differences ΔU i , where i=(1, 2 . . . , n), wherein the voltage differences ΔU i are determined during stable thermal conditions of the frequency converter;
determining a percentile value for each set of the voltage differences ΔU i in order to eliminate the highest errors occurring during determination of voltage differences ΔU i , wherein the elimination is done through rejection of values higher than the determined percentile, where i=(1, 2 . . . , n);
determining characteristic ΔU=f(P out ) from the values of the percentile,
determining a maximum allowable voltage difference ΔU maxallow , where
Δ U maxallow =⅓· U dc
where U dc represents a voltage of a DC-link circuit;
fixing a value of an output power limit P outlimit of the frequency converter for the determined maximum allowable voltage difference ΔU maxallow ;
assessing conditions of the DC-link capacitors, wherein when the value of the nominal power P n is higher than the fixed output power limit P outlimit the frequency converter is used conditionally with the power P i being selected to be lower than the fixed output power limit P outlimit without replacement of the at least two DC-link capacitors or at least two blocks of DC-link capacitors, where i=(1, 2 . . . , n).
9. The computer-implemented method according to claim 8 , wherein the value of the output power limit P outlimit of a frequency converter is periodically verified and/or updated.
10. The computer-implemented method according to claim 8 , wherein the DC-link circuit capacitors are electrolytic capacitors.
11. A system, comprising:
at least one frequency converter;
at least one monitoring apparatus; and/or
at least one server;
wherein the at least one monitoring apparatus and/or the at least one server is configured to communicate with the at least one frequency converter;
wherein the at least one monitoring apparatus and/or the at least one server is further configured to:
determine voltage differences ΔU i between at least two DC-link circuit capacitors or at least two blocks of DC-link circuit capacitors for each of at least two different values of an output power P out (i) of a frequency converter, thus providing at least two sets of the voltage differences ΔU i , where i=(1, 2 . . . , n), wherein the voltage differences ΔU i are determined during stable thermal conditions of the frequency converter;
determine a percentile value for each set of the voltage differences ΔU i in order to eliminate the highest errors occurring during determination of voltage differences ΔU i , wherein the elimination is done through rejection of values higher than the determined percentile, where i=(1, 2 . . . , n);
determine characteristic ΔU=f(P out ) from the values of the percentile,
determine a maximum allowable voltage difference ΔU maxallow , where
Δ U maxallow =⅓· U dc
where U dc represents a voltage of a DC-link circuit;
fix a value of an output power limit P outlimit of the frequency converter for the determined maximum allowable voltage difference ΔU maxallow .