Power transfer between phases in a transformer
An AC power transformer includes primary and secondary windings for at least a first AC phase and a second AC phase, and a core for said at least first and second phases. The transformer further includes a control unit for transferring power from the first phase to the second phase via magnetic coupling in the core such that the sum of the phase vectors of all of the at least first and second phases is substantially zero.
1. An AC power transformer for a three-phase system, the transformer comprising:
primary and secondary windings for a first AC phase, a second AC phase and a third AC phase;
a core for said at least first and second phases; and
a control unit configured for controlling mechanical and/or solid-state tap changing means of the first and second phases for transferring power from the first phase to the second phase via magnetic coupling in the core by changing the amplitude and the phase angle of the phase vectors of both the first phase and the second phase,
wherein the phase angles are changed such that the angle between the phase vectors of the first and second phases is not 120 degrees, such that the sum of the phase vectors of all of the first, second and third phases is substantially zero.
2. The transformer of claim 1 , wherein the control unit is configured for controlling power electronics connected to the first and second phases for said transferring power, said respective power electronics connected in series with each of the at least first and second phases.
3. The transformer of claim 2 , wherein said power electronics comprises a first AC converter connected to the primary winding of the first phase and a second AC converter connected to the primary winding of the second phase.
4. The transformer of claim 3 , wherein each of the first and second AC converters comprises an inductor or a capacitor.
5. An arrangement comprising:
the transformer of claim 2 ; and
a power converter connected in series with the transformer, on the secondary side of the transformer, for controlling the at least first and second phases.
6. The transformer of claim 2 , wherein the control unit is configured for controlling mechanical tap changers on the windings of the first and second phases for said transferring power.
7. An arrangement comprising:
the transformer of claim 3 ; and
a power converter connected in series with the transformer, on the secondary side of the transformer, for controlling the at least first and second phases.
8. The transformer of claim 3 , wherein the control unit is configured for controlling mechanical tap changers on the windings of the first and second phases for said transferring power.
9. An arrangement comprising:
the transformer of claim 4 ; and
a power converter connected in series with the transformer, on the secondary side of the transformer, for controlling the at least first and second phases.
10. The transformer of claim 4 , wherein the control unit is configured for controlling mechanical tap changers on the windings of the first and second phases for said transferring power.
11. The transformer of claim 1 , wherein the control unit is configured for controlling mechanical tap changers on the windings of the first and second phases for said transferring power.
12. An arrangement comprising:
the transformer of claim 11 ; and
a power converter connected in series with the transformer, on the secondary side of the transformer, for controlling the at least first and second phases.
13. An arrangement comprising:
the transformer of claim 1 ; and
a power converter connected in series with the transformer, on the secondary side of the transformer, for controlling the at least first and second phases.
14. The arrangement of claim 13 , wherein the transformer, by means of the transferring power, is configured for primarily controlling negative sequence currents of the phases, while the power converter is configured for primarily controlling positive sequence voltages of the phases.
15. A method of controlling a three-phase AC power transformer comprising primary and secondary windings for a first AC phase, a second AC phase and a third AC phase, and a core for said at least first and second phases, the method comprising:
transferring power from the first phase to the second phase via a magnetic coupling in the core by changing the amplitude and the phase angle of the phase vectors of both the first phase and the second phase,
wherein the phase angles are changed such that the angle between the phase vectors of the first and second phases is not 120 degrees, such that the sum of the phase vectors of all of the at least first and second phases is substantially zero.
16. The method of claim 15 performed by a control unit of the transformer by controlling mechanical and/or solid-state tap changing means of the first and second phases.
17. A computer program product comprising a non-transitory computer-readable storage medium having computer-executable components stored therein, the computer-executable components being configured to, when executed by processor circuitry comprised in the control unit for the transformer, cause the control unit for the power transformer to perform the method of claim 16 .
18. A computer program product comprising a non-transitory computer-readable storage medium having computer-executable components stored therein, the computer-executable components being configured to, when executed by processor circuitry comprised in a control unit for the power transformer, cause the control unit for the power transformer to perform the method of claim 15 .
19. A non-transitory computer readable medium storing computer program codes configured to control a three-phase AC power transformer comprising primary and secondary windings for a first AC phase, a second AC phase and a third AC phase, and a core for said at least first and second phases, the computer program comprising computer program code which is able to, when run on processor circuitry of a control unit for a phase leg of the power converter, cause the transformer to transfer power from the first phase to the second phase via a magnetic coupling in the core by changing the amplitude and the phase angle of the phase vectors of both the first phase and the second phase, wherein the phase angles are changed such that the angle between the phase vectors of the first and second phases is not 120 degrees, such that the sum of the phase vectors of all of the at least first and second phases is substantially zero.