ARRANGEMENT AND METHOD FOR A POWER BUS

Abstract

A method for a direct current (DC) power distribution arrangement and a direct current (DC) power distribution arrangement, comprising a plurality of DC power distribution subsystems. Each DC power distribution subsystem comprises an inverter unit (INU) configured to operate as a subsystem-specific circuit breaker for intercoupling/separating the DC power distribution subsystem to/from the rest of the DC power distribution arrangement.

Claims

1. A direct current (DC) power distribution arrangement, comprising a plurality of DC power distribution subsystems, wherein each DC power distribution subsystem comprises an inverter unit configured to operate as a subsystem-specific circuit breaker for intercoupling/separating the DC power distribution subsystem to/from the rest of the DC power distribution arrangement.

2. The DC power distribution arrangement according to claim 1, wherein the inverter unit is configured to operate as a subsystem-specific circuit breaker such that: the DC terminals of the inverter unit are connected to the corresponding DC poles of the DC power distribution subsystem, and each AC terminal of the inverter unit is connected to a terminal-specific connecting member, which terminal-specific connecting member is connected to an AC terminal of at least one other inverter unit connected to another DC power distribution subsystem.

3. The DC power distribution arrangement according to claim 2, wherein the number of connecting members is at least the same as the number of AC terminals of each inverter unit.

4. The DC power distribution arrangement according to claim 2, wherein the AC terminals of each inverter unit are connected to a unique combination of connecting members.

5. The DC power distribution arrangement according to claim 1, wherein the inverter units are configured to keep controllable power switches simultaneously in on-state in an upper or lower leg of one phase switch and in a lower or upper leg of either one another phase switch or of two other phase switches at a time.

6. The DC power distribution arrangement according to claim 5, wherein the inverter units are configured to keep the selected controllable power switches in on-state either: continuously; or for a predefined duration, in which case the on-state periods of the selected controllable power switches are configured to be rotated such that the average load of each AC terminal of the inverter unit is essentially equal.

7. The DC power distribution arrangement according to claim 1, wherein the DC power distribution arrangement comprises two DC power distribution subsystems and two inverter units, wherein the inverter units are configured to operate as pole-specific circuit breakers between the corresponding poles of the two DC power distribution subsystems such that: the first pole of the first DC power distribution subsystem is connected to a DC terminal of the first inverter unit, and the corresponding first pole of the second DC power distribution subsystem is connected to the intercoupled AC terminals of the first inverter unit, and the second pole of the first DC power distribution subsystem is connected to the intercoupled AC terminals of the second inverter unit, and the corresponding second pole of the second DC power distribution subsystem is connected to a DC terminal of the second inverter unit.

8. The DC power distribution arrangement according to claim 1, wherein the DC power distribution system comprises an upper level controller which is configured to turn on and/or off any controllable power switch in any inverter connected to the system.

9. The DC power distribution arrangement according to claim 8, wherein one DC power distribution subsystem is configured to be charged to the normal operating voltage level externally, and the upper level controller is configured to control the inverter unit connected to the fully charged subsystem to operate such that its pulse-width modulated output voltage rises at a predefined speed to the full level.

10. The DC power distribution arrangement according to claim 1, wherein the controllable power switches of at least one inverter unit in the system are configured to be kept turned off while at least two connection members are configured to be energized.

11. The DC power distribution arrangement according to claim 1, wherein in case of a measured overcurrent in one AC-terminal of an inverter unit, the connection member being connected to that AC-terminal is configured to be de-energized by turning off the controllable power switches at the AC-terminals connected to that specific connection member in all inverter units, and another replacement connection member is configured to be energized by turning on corresponding controllable power switches in another AC-terminal of all inverter units.

12. The DC power distribution arrangement according to claim 1, wherein the connecting member comprises an inductive component for limiting balancing current transients in switching situations.

13. A method for direct current (DC) power distribution arrangement, wherein the power distribution arrangement comprises a plurality of DC power distribution subsystems, each DC power distribution subsystem comprises an inverter unit, and the inverter unit operates as a subsystem-specific circuit breaker intercoupling/separating the DC power distribution subsystem to/from the rest of the DC power distribution arrangement.

14. The method in an arrangement according to claim 13, wherein the inverter units keep controllable power switches simultaneously in on-state in an upper or lower leg of one phase switch and in a lower or upper leg of either one another phase switch or of two other phase switches at a time.

15. The method according to claim 13, wherein the inverter units keep the selected controllable power switches in on-state either: continuously; or for a predefined duration, in which case the on-state periods of the selected controllable power switches are rotated such that the average load of each AC terminal of the inverter unit is essentially equal.

16. The method according to claim 13, wherein one DC power distribution subsystem is charged to the normal operating voltage level externally, and the upper level controller controls the inverter unit connected to the fully charged subsystem such that its pulse-width modulated output voltage rises at a predefined speed to the full level.

17. The method according to claim 13, wherein the controllable power switches of at least one inverter unit in the system are kept turned off while at least two connection members are energized.

18. The method according to claim 13, wherein in case of a measured overcurrent in one AC-terminal of an inverter unit, the connection member being connected to that AC-terminal is de-energized by turning off the controllable power switches at the AC-terminals connected to that specific connection member in all inverter units, and another replacement connection member is energized by turning on corresponding controllable power switches in another AC-terminal of all inverter units.

19. The DC power distribution arrangement according to claim 3, wherein the AC terminals of each inverter unit are connected to a unique combination of connecting members.

20. The DC power distribution arrangement according to claim 2, wherein the inverter units are configured to keep controllable power switches simultaneously in on-state in an upper or lower leg of one phase switch and in a lower or upper leg of either one another phase switch or of two other phase switches at a time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following, the invention will be described in more detail by the aid of some examples of its embodiments with reference to the attached drawings, wherein

[0021] FIG. 1 presents the main circuit of a frequency converter drive,

[0022] FIG. 2 presents a one-line diagram of a DC distribution power bus system,

[0023] FIG. 3A presents an arrangement in a DC power distribution bus system according to the first embodiment of the invention,

[0024] FIG. 3B illustrates timing diagrams related to the first embodiment of the invention,

[0025] FIG. 4A presents an arrangement in a DC power distribution bus system according to the second embodiment of the invention,

[0026] FIG. 4B illustrates a timing diagram related to the second embodiment of the present invention, and

[0027] FIG. 5 presents an arrangement in a DC power distribution bus system according to the third embodiment of the invention.

DETAILED DESCRIPTION

[0028] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms first, second, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms a and an do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of including, comprising or having and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms connected and coupled are not restricted to physical or mechanical connections: or couplings, and can include electrical connections or couplings, whether direct or indirect. Furthermore, the terms circuit and circuitry and controller may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together to provide the described function.

[0029] FIG. 1 presents a simplified main circuit diagram of a known and typical regenerative frequency converter as an example where the power units exploited in circuit breaker arrangements according to the present invention can be normally used.

[0030] In the example the converter comprises an active front end bridge AFE, which is able to feed power in both directions between the 3-phase mains network R, S, T, and the intermediate DC-circuit DC. AFE is connected to the mains via a so-called LCL line filter unit LFU, comprising a first 3-phase inductor unit LF.sub.1, a second 3-phase inductor unit LF.sub.2, and a capacitor unit C.sub.F. The inverter unit INU creates from the direct voltage circuit DC, which is filtered by a capacitor C.sub.D1, an adjustable 3-phase pulse width modulated (PWM) output voltage U, V, W, for supplying an AC motor M. AFE and INU bridges are similar, both consisting of 3 phase switches which are able to connect the phase terminal to either pole DC+, DC, of the DC intermediate circuit DC. One phase switch comprises of upper leg power components (i.e. a controllable power switch, normally IGBT, with an antiparallel-connected diode) connected to DC+ and similar power components in lower leg, connected to DC.

[0031] FIG. 2 presents an exemplary single-line drawing of a DC power distribution system wherein inverter units and active front end converters, as presented in FIG. 1, may be used. In this example, the DC power distribution system is divided into two subsystems DC.sub.1, DC.sub.2, which may be intercoupled or separated by a circuit breaker S.sub.1.

[0032] DC.sub.1 is powered by a diesel generator DG via an asynchronous generator ASG, a line filter unit LFU.sub.1 and an active front end converter AFE.sub.1. A motor drive, comprised of an inverter unit INU, and a motor M.sub.1 (feeding e.g. an air-conditioning fan) is an example of a typical load which may be connected to the system. A battery may be connected to the system in order to ensure the power stability (B.sub.1 via a voltage levels matching converter DC/DC.sub.1).

[0033] DC.sub.2 is in this example powered from the mains G.sub.2 via a transformer T.sub.2, a line filter unit LFU.sub.2 and an active front end converter AFE.sub.2. A couple of motor drives (INU.sub.2, M.sub.2, INU.sub.3, M.sub.3) are connected to DC.sub.2.

[0034] FIG. 3A presents an arrangement according to the present invention on how an arbitrary number of DC power distribution buses, in this example three buses DC.sub.31, DC.sub.32, DC.sub.33, can be intercoupled or separated by using three connecting members A, B, C, and DC bus specific inverter units INU.sub.31, INU.sub.32, INU.sub.33, as circuit breakers. The DC terminals +, , of each INU are coupled to the corresponding DC bus terminals and their AC terminals U, V, W to the phase-specific connecting members A, B, C.

[0035] FIG. 3B illustrates two methods on the coupling of the DC power distribution buses in the arrangement of FIG. 3A. In the diagrams a thick line with a + sign means that the connecting member is connected to the + pole of all DC distribution power buses. The connection is in practice made by turning on the upper leg power component of the phase switch connected to that connecting member. E.g. a thick A line with + sign means that the upper leg controllable power switches, such as IGBTs, of U-phase in all INUs are turned on. Correspondingly e.g. thick B line with sign means that the V-phase lower leg controllable power switches, such as IGBTs, of all INUs are turned on. The dotted line in the diagram means that there is no connection between the DC buses via that connecting member. E.g. a dotted line C means that in W-phase switches all controllable power switches, such as IGBTs, are turned off.

[0036] The upper part of FIG. 3B illustrates a method, wherein only two connecting members are in use at a time. In order to balance the average loads of power semiconductors and connecting members their operating sequences may be rotated at regular intervals as presented in the figure, at time instants t.sub.0, t.sub.1, t.sub.2, etc. This is called as dynamic loading method in this document. It is also possible to use static loading method by loading continuously only two connecting members, like e.g. A and C during time interval t.sub.0 . . . t.sub.1 in FIG. 3B, and keeping the free one (B) as a spare part. The spare part may in this example be put into service e.g. in a situation where connection member C gets ground-faulted, by turning off all controllable power switches, e.g. IGBTs, in W-phase and turning on corresponding controllable power switches in V-phase.

[0037] The lower part of FIG. 3B illustrates a method, wherein all connecting members are used continuously (i.e. all phase switches of all INUs are continuously active). In order to balance the average loads of power semiconductors and connecting members the periods during which two members are connected to the + poles of the DC buses and one member to the pole, or vice versa, are rotated at regular intervals at time instants t.sub.0, t.sub.1, t.sub.2, etc. A static loading method is possible also in this case, by using the same connection members continuously.

[0038] FIG. 4A presents an arrangement according to the present invention on how an arbitrary number of DC power distribution buses, in this example 5 buses DC.sub.41 . . . DC.sub.45, can be intercoupled or separated by using 5 connecting members D, E, F, G, H, and DC bus specific inverter units INU.sub.41 . . . INU.sub.45 as circuit breakers. The DC terminals +, , of each INU is coupled to the corresponding DC bus terminals and their AC terminals U, V, W to the connecting members such that each connection combination is dissimilar. The dissimilarity connection combination requirement sets the requirement to the number of connecting members; e.g. in case of 5 DC power buses the number of connecting members has to be at least 5.

[0039] FIG. 4B illustrates a method on how the DC power distribution buses DC.sub.41 . . . DC.sub.45 may be intercoupled. In the method, each connecting member is connected to the + or pole of at least two DC power buses. In order to balance the average loads of power semiconductors and connecting members the operating periods may be rotated similarly to what is presented e.g. above in FIG. 3B (rotation instants t.sub.10; t.sub.11). Instead of this dynamic loading method, a similar static loading method, as presented in description of FIG. 3, is possible also in this case by using the same connection members continuously.

[0040] The benefit of this arrangement and method is that a faulty DC bus can be isolated such that the undamaged DC buses may stay intercoupled and continue operating normally. An example of this protection method is illustrated in FIG. 4B after the time instant t.sub.12 where the DC.sub.41 bus gets short-circuited. The short-circuit means that all connecting members D, E, F are also short-circuited via the freewheeling diodes of INU.sub.41. In a method embodiment related to this arrangement, the connecting members coupled to the faulty DC bus are connected to one of the poles of the undamaged DC buses (in this example D, E, F are connected to the pole), and the rest of the connecting members are connected to the opposite pole (i.e. G and H are connected to the + pole).

[0041] FIG. 5 presents an arrangement according to the present invention on how two DC power distribution buses DC.sub.51, DC.sub.52, can be intercoupled or separated by using two inverter units INU.sub.51, INU.sub.52 as circuit breakers. In the arrangement the intercoupled AC terminals of the first INU are connected to the + pole of the first DC bus and the DC+ terminal to the second DC bus. In pole side the DC terminal of another INU is connected to the first DC bus and the intercoupled AC terminals to the second DC bus. The DC buses can be separated by turning off all controllable power switches, such as IGBTs, because then no balancing current can flow between the DC buses due to the same conducting direction of the freewheeling diodes in both poles. The DC buses can be intercoupled by turning on the controllable power switches, balancing current can then flow via controllable power switches in one pole and diodes in another pole. Due to the parallel-connected phase switches the loadability of the circuit breaker arrangement is maximum what can be reached by using a standard INU module.

[0042] In an embodiment related to this arrangement, the controllable power switches of an INU are controlled so that all three phase switches are always in the same position.

[0043] While the invention has been described with reference to the previous embodiment, it should be recognized that the invention is not limited to this embodiment, but many modifications and variations will become apparent to persons skilled in the art without departing from the scope of the invention, as defined in the appended claims.