ARRANGEMENT, METHOD AND COMPUTER PROGRAM PRODUCT CONCERNED WITH TAPPING OF POWER FROM A DC POWER LINE TO AN AC POWER LINE
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0 Petitions
Accused Products
Abstract
An arrangement for tapping power from a DC power line to an AC power line includes power transfer modules between two DC potentials, each including a first branch with a string of converter cells in parallel with a second branch including a capacitor and being connected to an AC phase. There is at least one control unit that controls the arrangement considering one or more of a) distributing appropriate AC and DC voltages in converter output voltages of all series connected modules, b) maintaining/setting cell capacitor voltages in specific range and allowing boost mode operation, c) performing possible balancing of the introduced capacitor and d) employing an alternate approach of using passive filters to mitigate low order harmonics.
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Citations
39 Claims
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1-19. -19. (canceled)
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20. An arrangement for converting between alternating current, AC, and direct current, DC, said arrangement comprising:
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a number of power transfer modules connected in series between two DC potentials, where one DC potential is the voltage of a DC power line and each power transfer module comprises a first branch comprising a string of converter cells, wherein a cell provides a voltage contribution of a cell capacitor or zero, said first branch being connected in parallel with a second branch comprising a capacitor and a secondary winding of a transformer, the primary winding of which is connected to a corresponding AC phase of an AC network; at least one control unit comprising; an adding unit configured to; obtain an AC voltage reference and a DC dependent control contribution, said DC dependent control contribution being based on a DC voltage term depending on the number of power transfer modules and on the difference between the two DC potentials; and add the DC dependent control contribution to the AC voltage reference for forming a first control expression; and a dividing unit configured to; obtain the first control expression; obtain a cell voltage reference sum for use in a second control expression, where the cell voltage reference sum is a sum of cell capacitor voltage references provided for a corresponding power transfer module; and divide the first control expression with the second control expression in order to obtain a reference voltage signal for use in PWM control of the cells of the string of a corresponding power transfer module, where the signal is compared with a triangular carrier wave. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 39)
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32. A method of controlling a power transfer module for converting between alternating current, AC, and direct current, DC, the power transfer module being a power transfer module in a group of power transfer modules connected in series between two DC potentials, where one DC potential is the voltage of a DC power line and each power transfer module comprises a first branch comprising a string of converter cells, wherein a cell provides a voltage contribution of a cell capacitor or zero, said first branch being connected in parallel with a second branch comprising a capacitor and a secondary winding of a transformer, the primary winding of which is connected to a corresponding AC phase of an AC network, the method comprising:
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obtaining an AC voltage reference; obtaining a DC dependent control contribution, said DC dependent control contribution being based on a DC voltage term depending on the number of power transfer modules and the difference between the two DC potentials; adding the DC dependent control contribution to the AC voltage reference for forming a first control expression; obtaining a cell voltage reference sum for use in a second control expression, where the cell voltage reference sum is a sum of cell capacitor voltage references provided for a corresponding power transfer module; dividing the first control expression with the second control expression for obtaining a reference voltage signal for PWM control; and PWM controlling the cells of the string of the power transfer module using said reference voltage signal as a control signal in PWM control of these cells where the signal is compared with a triangular carrier wave. - View Dependent Claims (33, 34, 35, 36, 37)
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38. A computer program product for controlling a power transfer module for converting between alternating current, AC, and direct current, DC, the power transfer module being a power transfer module in a group of power transfer modules connected in series between two DC potentials, where one DC potential is the voltage of a DC power line and each power transfer module comprises a first branch comprising a string of converter cells, wherein a cell provides a voltage contribution of a cell capacitor or zero, said first branch being connected in parallel with a second branch comprising a capacitor and a secondary winding of a transformer, the primary winding of which is connected to a corresponding AC phase of an AC network, the computer program product comprising a non-transitory data carrier with computer program code configured to cause a control unit to:
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obtain an AC voltage reference; obtain a DC dependent control contribution, said DC dependent control contribution being based on a DC voltage term depending on the number of power transfer modules and the difference between the two DC potentials; add the DC dependent control contribution to the AC voltage reference for forming a first control expression; obtain a cell voltage reference sum for use in a second control expression, where the cell voltage reference sum is a sum of cell capacitor voltage references provided for a corresponding power transfer module; divide the first control expression with the second control expression for obtaining a reference voltage signal for PWM control; and PWM control the cells of the string using said reference voltage signal as a control signal in PWM control of these cells where the signal is compared with a triangular carrier wave.
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Specification