Method of and apparatus for compensation of oscillation effects in the event of mains asymmetry in a double-fed asynchronous machine
In a method for the compensation of rotor torque oscillations upon the occurrence of mains asymmetries in relation to a double-fed asynchronous machine ( 1 ) it is provided that at least one respective currently prevailing machine parameter is measured and/or derived, the at least one machine parameter is respectively decomposed by calculation into a positive and a negative sequence system component and optionally a DC component, and for the positive sequence system component, the negative sequence system component and optionally for the DC component of the at least one machine parameter, there are respective separate control members for controlling an adjusting value, to which the respective components of the machine parameters are fed as input components and the output values of which are additively superposed. In that case the control members are so adapted for controlling the adjusting value in such a way that the torque oscillations are counteracted. Alternatively there is provided a control member to which the cross-product of the positive sequence system components and negative sequence system components as well as the cross-product of the negative sequence system components and positive sequence system components are fed as an input value, the control member being so adapted for controlling the adjusting value in such a way that second-order torque oscillations are counteracted.
1. A method for compensating rotor torque harmonics in a double-fed asynchronous machine fed by a frequency converter controlled by a control unit, comprising the steps of:
measuring at least one current machine parameter or deriving at least one current machine parameter from machine measurement parameters;
decomposing the at least one current machine parameter into a positive system component and a negative system component;
supplying the positive system component of the at least one machine parameter to an input of a first control member and supplying the negative system component of the at least one machine parameter to an input of a second control member;
adding a first output value from the first control member and a second output value from the second control member to produce a control variable; and
controlling the control variable so as to counteract torque oscillations.
2. The method of claim 1 , wherein the at least one current machine parameter is further decomposed into DC component, and further comprising the step of supplying the DC component of the at least one machine parameter to an input of a third control member, and adding a third output value from the third control member to the first and second output values.
3. The method of claim 1 , wherein the at least one machine parameter comprises one or more machine parameters selected from the group of a current rotor flux vector and a current stator flux vector; a network voltage and a network current; a stator voltage and a stator current, a rotor voltage and a rotor current, and a voltage and a current at a network-side converter member of the frequency converter.
4. A method for compensating rotor torque harmonics in a double-fed asynchronous machine fed by a frequency converter controlled by a control unit, comprising the steps of:
measuring at least one current machine parameter or deriving at least one current machine parameter from machine measurement parameters;
decomposing the at least one current machine parameter into a positive system component and a negative system component;
supplying to at least one control member a cross-product of the positive system component and the negative system component, and a cross-product of the negative system component and the positive system component as an input value to produce at an output of the at least one control member a control variable; and
controlling the control variable so as to counteract second-order torque oscillations.
5. The method of claim 1 , and further providing additional fourth control members for suppressing higher-order harmonics of a mains frequency.
6. The method of claim 5 , wherein the higher-order harmonics are sixth and the twelfth harmonics.
7. The method for claim 1 , wherein the at least one machine parameter comprises a current stator flux vector and a current rotor flux vector which are computed with a flux monitor from actual measured current and voltage values of the machine,
wherein positive system components of the rotor and the stator are supplied to the input of the first control member and the negative system components of the rotor and the stator are supplied to the input of the second control member, and
wherein the control variable comprises a phase shift φ 0 and a reduction factor k red and
the following relationship between the stator and rotor flux vectors is controlled:
ψ
_
1
p
ψ
_
2
p
′
=
ψ
_
1
n
ψ
_
2
n
′
=
1
k
red
and
∠
ψ
_
2
p
′
=
∠
ψ
_
1
p
+
ϕ
0
and
∠
ψ
_
2
n
′
=
∠
ψ
_
1
n
-
ϕ
0
with ψ 1p and ψ 2p ′ representing positive system components of the stator and rotor, respectively, ψ 1n and ψ 2n ′ representing negative system components of the stator and rotor, respectively,
wherein the phase shift φ 0 is adjusted to adjust a resulting torque, and k red is selected in dependence on a maximum available adjusting value of the rotor voltage.
8. The method for claim 2 , wherein the at least one machine parameter comprises a current stator flux vector and a current rotor flux vector which are computed with a flux monitor from actual measured current and voltage values of the machine,
wherein positive system components of the rotor and the stator are supplied to the input of the first control member and the negative system components of the rotor and the stator are supplied to the input of the second control member, and the DC components of the current stator flux vector and a current rotor flux vector are supplied to the input of the third control member,
wherein the control variable comprises a reduction factor k red and
the following relationship between the stator and rotor flux vectors is controlled for a total torque of zero:
ψ
_
1
p
ψ
_
2
p
′
=
ψ
_
1
n
ψ
_
2
n
′
=
ψ
_
1
dc
ψ
_
2
dc
′
=
1
k
red
and
∠
ψ
_
2
p
′
=
∠
ψ
_
1
p
and
∠
ψ
_
2
n
′
=
∠
ψ
_
1
n
and
∠
ψ
_
2
dc
′
=
∠
ψ
_
1
dc
′
wherein k red is selected in dependence on a maximum available adjusting value of the rotor voltage.
9. A control unit for controlling a double-fed asynchronous machine in the event of occurrence of mains asymmetries, wherein the machine comprises a frequency converter actuated by the control unit, the control unit controlling the converter in regard to a predetermined control strategy, wherein the control unit compensates rotor torque harmonics by performing the method of claim 1 .
10. The method of claim 1 , wherein the rotor torque harmonics comprise second harmonics.
11. The method of claim 1 , wherein the double-fed asynchronous machine is a separate exited three-phase machine.
12. The method of claim 4 , wherein the at least one machine parameter comprises one or more machine parameters selected from the group of a current rotor flux vector and a current stator flux vector; a network voltage and a network current; a stator voltage and a stator current, a rotor voltage and a rotor current, and a voltage and a current at a network-side converter member of the frequency converter.
13. The method of claim 4 , wherein the at least one machine parameter comprises a current stator flux vector and a current rotor flux vector which are computed with a flux monitor from actual measured current and voltage values of the machine, and
wherein the control variable is a negative system component of the rotor flux, which is controlled in such a way that a negative vector product of a positive system component of the stator flux with the negative sequence system component of the rotor flux is equal to a vector product of a negative sequence system component of the stator flux with a positive sequence system component of the rotor flux expressed as
− ψ 1p × ψ 2n ′= ψ 1n × ψ 2p ′,
wherein ψ 1p and ψ 2p ′ represent the positive system components of the stator and rotor, respectively, and ψ 1n and ψ 2n ′ represent the negative system components of the stator and rotor, respectively.
14. The method of claim 13 , wherein the control variable is controlled by generating a virtual spatial vector and eliminating a difference in respect of magnitude and phase is eliminated with two PI regulators with a feed-forward term.
15. The method of claim 14 , wherein the control variable is controlled by limiting a control signal of a rotor-side inverter of the converter by taking into consideration a maximum available control signal.
16. A control unit for controlling a double-fed asynchronous machine in the event of occurrence of mains asymmetries, wherein the machine comprises a frequency converter actuated by the control unit, the control unit controlling the converter in regard to a predetermined control strategy, wherein the control unit compensates rotor torque harmonics by performing the method of claim 4 .
17. The method of claim 4 , wherein the double-fed asynchronous machine is a separate exited three-phase machine.