Abstract
A power transformation system that is constructed and arranged to transform power from one or more primary voltage nodes to a separate secondary voltage node using one or more columns comprised of a plurality of capacitive modules each of which is capable of being either electrically inserted into the column or electrically isolated and electrically bypassed. There is a secondary voltage node, at a non-ground potential, to which a first end of the column is electrically connected. In the two-primary node example there are two high voltage switches, each in series with a reactor; one high-voltage switch adapted to electrically connect a second end of the column to the first primary voltage node and the other high-voltage switch adapted to electrically connect the second end of the column to a second primary node. A controller is adapted to control high voltage switches to connect the capacitances comprising the column sequentially to each primary node so as to transform power, by resonant exchange of energy, between those primary nodes and the secondary node.
Claims
1. A power transformation system that is constructed and arranged to transform power from one or more primary voltage nodes to a separate secondary voltage node, the system comprising: (a) one or more columns, each column comprising a plurality of capacitive modules, where the capacitive modules comprise a plurality of series-connected capacitances that are arranged to be either electrically inserted into the column or electrically isolated and electrically bypassed; (b) a secondary voltage node that is at a non-ground potential, wherein a first end of a column is electrically connected to the secondary voltage node; (c) multiple high voltage switches, each in series with a column; each high-voltage switch adapted to electrically connect, sequentially, a second end of the column to a primary voltage node; (d) a fourth node that is at a ground potential; (e) a capacitor that is electrically connected between the secondary node and the fourth node, wherein the capacitor has a susceptance that is larger than a susceptance of the columns; and (f) a controller adapted to control the connections of the capacitances within a column and two high voltage switches that are in series with the column, so as to transform power by resonant exchange of energy between multiple capacitances within the column and both primary and secondary nodes.
2. The power transformation system of claim 1, wherein an aggregate voltage rating of all capacitive modules comprising a column exceeds the voltage of any oldie primary voltage nodes.
3. The power transformation system of claim 1, wherein the primary nodes are high voltage DC nodes.
4. The power transformation system of claim 3, wherein the resonant exchange comprises a repeating cycle of sequential charge exchanges with each of the primary nodes, and wherein the controller is further adapted to control one or both the number and configuration of series-connected capacitive modules comprising the capacitive column, such that a terminal-to-terminal voltage of the capacitive column is changed from one step in the capacitive column charge exchange cycle and the next.
5. The power transformation system of claim 4, wherein the controller is further adapted to configure the potential of the secondary voltage node to be equal to the voltage of any one of the primary voltage nodes minus the terminal-to-terminal voltage of the capacitive column.
6. The power transformation system of claim 5, wherein the controller is further adapted to prevent the potential of the secondary voltage node from drilling from its nominal value.
7. The power transformation system of claim 5, wherein the controller is further adapted to reconfigure the capacitive column from one cycle to the next such that the potential of the secondary voltage node varies in a manner approximating a sinusoid.
8. The power transformation system of claim 7, wherein the capacitive column is configured such that its voltage is greater than the voltage of any of the primary voltage nodes, thereby allowing the voltage on the secondary node to be a full sinusoidal voltage, with positive and negative half-cycles that are equal in voltage magnitude with respect to ground.
9. The power transformation system of claim 8, comprising multiple capacitive columns that are controlled to simultaneously transform power from one or more primary nodes to three secondary nodes each one of which represents one phase of a three phase AC node.
10. The power transformation system of claim 9, wherein the DC primary nodes are bipolar, each pole of which is configured to transform power to a three-phase AC node set.
11. The power transformation system of claim 1, configured to transform power between primary DC nodes and an additional DC secondary node, all of which are bipolar DC nodes.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 shows the prior art configuration necessary to connect the juncture of two DC transmission lines to an AC system in a self-redundant manner using prior art equipment.
(2) FIG. 2 shows a prior art schematic of a capacitive column DCT, based on prior art, when connected to exchange charge with the first of two DC nodes.
(3) FIG. 3 shows a prior art schematic of a capacitive column DCT, based on prior art, when connected to exchange charge with the second of two DC nodes.
(4) FIG. 4 shows the prior art pulsed nature of input and output current profiles for a single capacitive column DCT.
(5) FIG. 5 shows a prior art three capacitive column DCT that is configured to increase power exchange capability and cause smoother input and output current wave-shapes.
(6) FIG. 6 shows the prior art smoothing effect on both input and output wave-forms achieved by using the three-capacitive column DCT of FIG. 5.
(7) FIG. 7 shows a prior art three capacitive column-based DCT used to transform power between two bipolar DC nodes.
(8) FIG. 8 shows a prior art adaptation of the configuration in FIG. 7 for the case where no ground is established in transformation between two bipolar DC nodes.
(9) FIG. 9 shows a prior art simplification of the configuration shown in FIG. 8.
(10) FIG. 10 shows a system of the present disclosure where the junction of positive and negative capacitive columns is isolated from ground and caused to assume a voltage equal to the difference between positive and negative column voltages.
(11) FIG. 11 shows a simplified example of embodiments that include an additional bus with a non-ground voltage which functions as a third independent node.
(12) FIG. 12 shows extension of FIG. 11, using a three-column DCT for each of two poles, each pole supplying its own third independent node.
(13) FIG. 13 shows a power frequency half-sine wave approximated by successive DCT charge exchanges, each changed in ratio from the prior.
(14) FIG. 14 shows the division of voltage within the configuration of FIG. 11 when it is used to generate an AC wave-form.
(15) FIG. 15 shows the addition of a grounding reactor to prevent build-up of DC voltage on the offset-neutral node.
(16) FIG. 16 shows the system and method of FIG. 15 wherein the second DC bus is eliminated, thus constituting a bipolar DC to three-phase AC transformer.
(17) FIG. 17 shows how transformation can be achieved between either or both of two monopolar DC nodes and a set of three-phase AC nodes.
(18) FIG. 18 extends FIG. 17 to show transformation of power between bipolar DC nodes and a set of three-phase AC nodes.
(19) FIG. 19 illustrates use of the embodiments in simplifying the interconnection of incoming DC transmission lines in the underlying AC system.
DETAILED DESCRIPTION
(20) FIG. 10 illustrates a DC-to-DC transformation similar to that shown in FIG. 7 but with the juncture of positive and negative capacitive columns connected to a common node 6 at some electrical potential, ΔV, other than ground by causing voltages V.sub.1+ and V.sub.1− to be unequal and V.sub.2+ and V.sub.2− to also be unequal while the absolute sum of V.sub.1+ and V.sub.1− remains equal to node-to-node primary voltage and the absolute sum of V.sub.2+ and V.sub.2− equal to the secondary node-to-node voltage. The result is a voltage displacement of node 6 above ground potential by ΔV=|V.sub.1+|−|V.sub.1−|=|V.sub.2+|−|V.sub.2−|; thus, adding to the DCT another node of voltage ΔV. Functions of this additional node 6 are further described below.
(21) The voltage displacement of node 6, ΔV, can be realized as disclosed in principle by FIG. 11. In that elementary embodiment, the voltage of the column can be decreased between connection to nodes 2 and 3 by electrically by-passing modules within the column 100 or increased by electrically inserting in series with the column, modules that were previously charged in a “sorting process,” i.e., one in which, during connection to either node 2, 3, the number of capacitive modules in electrical series was kept constant but sequentially shared by multiple columns.
(22) In order that the resonant discharge of the capacitor column have a path to the ground node 1 and that it appear predominantly between a secondary node 6 and ground, a capacitor 10 must be inserted connecting that secondary node 6 and ground 1 and, further, that capacitor 10 which will contribute to the resonant frequency of discharge of the column 100, must have a capacitance much smaller than the capacitance of the column 100, i.e., its susceptance must be much larger than that of the column.
(23) The principle illustrated by FIG. 11 for a monopolar DC case can be extended to include three capacitive columns 100, each of which is assigned a switching cycle offset equally from the others as was illustrated in FIG. 3, and extended further by addition of a mirror image configuration supplied by the negative polarity first nodes 4, 5 as shown in the embodiment illustrated in FIG. 12. In that embodiment the additional node 6, supplied by the positive nodes 2, 3 will itself be positive in polarity and the additional node 7, supplied by the negative first nodes 4, 5, will be negative in polarity.
(24) Prior art has shown that the typical resonant frequency of half-sine-wave charge/discharge cycles of a column-based DC-to-DC transformer, being an order of magnitude higher than power frequencies, can allow the DC-to-DC transformation ratio of an MMDCT to be varied from one charge/discharge cycle to the next to approximate a power frequency half-sine wave as shown in FIG. 13. Thus, by varying the number of capacitive modules in the elementary single-column transformer of FIG. 11, an embodiment using that configuration can also be made to approximate a half-cycle of power frequency voltage. In doing so FIG. 14 shows that during steps in the cycle where the capacitive column 100 is connected to node 2, the capacitive modules within the capacitive column 100 must be selected such that the voltage across the column 100, V.sub.c, must be such that V.sub.2+−V.sub.c=V.sub.ac, and since the column is rapidly switched between DC nodes 2 and 3, that during connection to node 3, V.sub.c is such that V.sub.3+−V.sub.C=V.sub.ac. FIG. 14 shows that, while achieving the required column voltage by appropriate selection of capacitive modules in series is obvious for the positive half-cycle, achieving it for the negative half cycle of the AC wave requires that (1) sufficient capacitive modules be in place such that their cumulative voltage rating of all capacitive modules is substantially higher than the higher of the two DC node voltages and (2) that subgroups of the total number of capacitive modules be separately charged to the DC voltage such that, when it is necessary that the (subtracting) column voltage, V.sub.C be greater than the DC node voltage, V.sub.2+ or V.sub.3+, sufficient voltage can be achieved within the capacitive column 100.
(25) Thus, the elementary embodiment shown in FIG. 11 can transform between a monopolar DC node and a single phase alternating current node with equal positive and negative voltages with respect to a ground node 1. As with the prior art DC-DC transformer configuration illustrated in its elementary form by FIG. 2, periodic adjustment of the specific number of capacitive modules within the capacitive column 100, can control the direction and magnitude of power transfer between any two of the three nodes 2, 3, 6 shown in FIG. 11.
(26) It should be noted that with the embodiment of FIG. 11 adapted to DC-AC-DC operation, slight inconsistencies in voltage from one operating cycle to another could cause a build-up of DC voltage on the grounding capacitor 10. To prevent that a reactor 11 can be inserted between bus 6 and ground as shown in FIG. 15.
(27) In any multi-module DCT based on the principles shown FIGS. 2 and 3, power transfer between nodes 2 and 3 in that case can be adjusted in magnitude and direction by adjustment of the number of capacitive modules in place while the capacitive column exchanges charge with node 1 and the number in place during charge exchange with node 3. If the column's capacitive module configuration is made to present a voltage of exactly V.sub.1 to node 2 and exactly V.sub.2 to node 2, no power will be transferred between those two nodes 2, 3 as the transformation cycle is repeated. Thus if, in the embodiment of FIG. 11, no power is to be transmitted between nodes 2 and 3, the switch 13 serves no purpose and can be eliminated along with its associated reactor 70 as shown in FIG. 16.
(28) Furthermore it will be apparent from explanation of the embodiment shown in FIG. 15 wherein a single capacitive column 100 served by two DC nodes 2, 3, was shown capable of transforming power between those monopolar DC nodes 2, 3, and a single-phase AC node 6, that this embodiment can be extended by using three capacitive columns as shown in FIG. 17, that three such configurations, connected to the same monopolar nodes 2,3 can transform power between those DC nodes 2, 3 and each of three AC nodes 200, 201, 202. comprising a three phase AC source. It is further apparent from FIG. 18 that adding a mirror image of the DCT embodiment shown in FIG. 17 to that shown in FIG. 17 would, as shown in FIG. 18, allow bipolar DC node pairs 2, 3 and 3, 4 to exchange power with a three phase AC node set 200, 201, 203.
(29) Within all the above cited embodiments, power flow between any two bipolar DC voltage sources will respond either to changes in the relative primary and secondary DC voltages presented to the DCT due to system operation or to a deliberate adjustment of the number of capacitive modules bypassed during connection to the lower of the DC voltages, i.e. manual control.
(30) While explanation of some of the foregoing embodiments have been illustrated by use of a single capacitive column 100, 101 for the sake of simplifying explanation, it will be apparent that each embodiment can be extended to use multiple capacitive columns in parallel, each equally offset in timing from the other, to produce smoother input and output voltage and current wave-forms and, further, that prior art filters can further smooth those waveforms.
(31) The general schematic of FIG. 1 illustrated the principle of self-redundancy. FIG. 19 illustrates that the same degree of redundancy can be achieved by incorporating the embodiment cited above into a DC-AC-DC transformer 9, using a simpler array of components than was shown in FIG. 1 while simultaneously allowing power transfer between multiple incoming DC lines without double DC/AC transformation. The embodiments cited herein also allow continuity of DC to AC power transfer despite the loss of one DC pole or, for multiple DC taps of small rating, DC to AC exchange from just one DC polarity.
(32) A number of implementations have been described. Nevertheless, it will be understood that additional modifications may be made without departing from the scope of the inventive concepts described herein, and, accordingly, other embodiments are within the scope of the following claims.
