WO2013098744A2

WO2013098744A2 - Method and apparatus for inrush mitigation in power distribution systems

Info

Publication number: WO2013098744A2
Application number: PCT/IB2012/057623
Authority: WO
Inventors: Bozena Erdmann; Michael Alex VAN HARTSKAMP; Matthias Wendt; Maurice Herman Johan Draaijer; Manuel Eduardo ALARCON-RIVERO
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-12-27
Filing date: 2012-12-21
Publication date: 2013-07-04
Also published as: WO2013098744A3

Abstract

The present invention relates to design-and installation-time tool for solving the inrush problem. The proposed design and planning tool for DC power distribution networks takes into account the inrush behavior of the loads and distributes the loads likely to be switched on at the same time (e.g. being members of one control group) to different bus bars.

Description

METHOD AND APPARATUS FOR INRUSH MITIGATION IN POWER DISTRIBUTION SYSTEMS

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for inrush mitigation or inrush current limitation in power distribution systems.

BACKGROUND OF THE INVENTION DC (direct current) power distribution are estimated to provide upcoming, promising simplifications of load power components, energy saving by reduction of distribution and conversion losses as well as simplified integration of local green energy sources. But, DC power distribution systems often suffer from inrush - the effect of increased current consumption on device power on. Unlike done in alternating current (AC) systems, a DC load can beneficially have a capacitor at the power input terminals. Such a capacitor prevents that the current ripple of the load itself propagates fully to the power grid and smoothes spikes, especially short overvoltage pulses, in order to protect the load. But, such input capacitors would produce excessive currents whenever the grid needs to be powered up as all capacitances need to be charged at once. A specific source for inrush are e.g. lighting devices based on halogen incandescent lamps, as the filament needs a multiple of nominal current until the lamp gets on temperature. Also, a typical inrush condition is when the grid voltage rises slowly at a certain voltage loads with switched mode, as power supplies will try to start up. As long as the voltage is below nominal value the required supply current is often higher than the nominal current to deliver the nominal power into the load.

There are specific requirements and standards for limiting the available power per bus bar which is a strip made of e.g. copper or aluminum that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. For example, EMerge Alliance specification requires for the low- voltage (24V) DC installations conformance with NFPA® National Electric Code safety regulations, thus limiting the available power to 100VA per bus bar. In DC systems, inrush causes temporal exceeding of the allowable power budget on the bus bar, and thus temporal disconnection of the bus bar and unpowering of the devices supplied by it, an effect very disturbing to the user, especially if happening repeatedly, as likely on system startup. Inrush protection via electronic circuitry in the load may be costly.

Disadvantages of inrush are e.g. temporary power and equipment unavailability on startup, due to exceeded current limit, and user-noticeable power on/off effects caused by inrush and protection, like lights flashing, and systems failing to switch on after power drop.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatus for limiting inrush current in power distribution systems.

This object is achieved by an apparatus as claimed in claim 1, by a method as claimed in claim 6, and by a computer program product as claimed in claim 7.

Accordingly, inrush prevention is provided for DC power distribution system planning and installation assistance, which allows the user to define control groups for the DC powered loads and which is equipped with a feature to analyse the inrush behavior of the loads and propose an installation way such that the power limitations are met even in the startup phase.

For example, in the lighting control systems, especially in the professional lighting segment targeted by EMerge, lamps are often assigned to groups. For example, all lamps in one room may all be automatically controlled by a presence detector, or lamps in one room may be assigned to different groups, controlled by light sensors (e.g. for daylight integration at the window-side/corridor-side office lighting), or multiple workplace- or task-assigned buttons. In another example, enabling a hotel room before guest's arrival may require turning on of HVAC, default lighting and television (TV) for basic guest information or the like. In yet another example, powering a workplace may require turning on a desktop, a screen, a printer, loudspeakers and a smartphone docking station.

The inrush prevention tool can be a dedicated device, a function of a device, or an application running on a generic purpose platform, local or remote. The device implementing the tool function can be portable, handheld or stationary. The inrush prevention tool may analyse the inrush behavior of the planned loads and proposes a way of their installation such that the power limitations are met even during the startup phase. To this end, the inrush prevention tool allows the user to specify the planned loads and their key characteristics.

This can be achieved by selecting a load type/model from a tool database, downloading load/type model characteristics form its vendors webpage, or allowing the user to specify key characteristics of the load, e.g. average/maximum operational current/power, inrush current, inrush duration. The input can be performed in user-friendly graphical form, textual form, by scanning of some product labels, etc.

Furthermore, the inrush prevention tool may allow for assignment of the loads to groups.

The input can be performed in user-friendly graphical form, textual form, by scanning of some product labels, etc. If the inrush prevention tool is integrated with some other functionality, e.g. floor plan functionality and installation drawing, the inrush prevention tool could even automatically propose some default groups to the user. For example, with one group per room, or two groups in each room, with one group containing one load alongside the window. Then, the inrush prevention tool may analyse the available information about the loads and their control grouping, so as to analyse the inrush behavior.

In one embodiment, the user may also be required to input the information on the planned DC grid, incl. the number of bus bars available, and how many loads are planned to be attached to each of the bus bars. Then, the tool analyses the inrush behavior and indicates bus bar with inrush over-current. In extension, it can also propose some remedies.

In another embodiment, the tool can be connected to one or multiple locations of the DC power distribution system and some parameters of the DC grid can be automatically discovered (e.g. by monitoring current waveforms during operation).

In yet another embodiment, the user may not be required to provide any information about the DC grid, while the planning of the complete DC power distribution system, including the inrush protection, may be done by the inrush prevention tool. For the purpose of limiting the inrush, the loads may get re-distributed over bus bars. The possible means are for example: splitting a group of loads likely to cause inrush over-current to different bars, changing the orientation of the bus bars from along the room axis (e.g. from parallel to the window wall to perpendicular to the window wall), attaching the loads to the internal and external bus bar of the same bar, if the bus bars are not connected, shifting the loads to another bus bar, or increasing the density of the bus bars, e.g. by using shorter bus bars or spacing the bus bars physically closer apart.

Furthermore, especially for bus bars already operating close to the maximum power conditions, the inrush prevention toll may be adapted to avoid putting together on the same bus bars loads with different reliability requirements or loads with different operational cycle. For example, a continuously operated load (corridor light) may not be disturbed by frequently switched on/off light, e.g. one in coffee/printer corner. Moreover, loads never or unlikely to be used together may be put on the same bus bar.

Additionally, the inrush prevention tool may also be adapted to analyze other unfavourable power conditions on the bus bar, e.g. overload during operation. More specifically, the inrush prevention tool tool could take additional requirements/boundary conditions into account, such as (i) total cost of (BoM) installation, (ii) cost/time for performing the installation, (iii) condition to protect against (worst case / average operational case); (iv) other operational criteria, e.g. expected power losses due to standby power of power supply module, standby power of the loads on powered bars, losses in the bars, etc., (v) application-related requirements and conditions, e.g. in case of lighting: required amount of lux in certain locations, (vi) boundary conditions imposed by the control technology, e.g. length/range/capacity of the control channel, control architecture, etc.

As a further option, the inrush prevention tool may allow for defining application-related requirements and conditions. More specifically, the inrush prevention tool may allow the user to specify high-level requirements, e.g. dimensions of the room, presence of door/window/glass walls, number of participants, required amount of illumination and/or preferred brand, type and/or usage of loads (e.g. halogen accent lights, general purpose TL lights), and the tool will provide the complete design, incl. the ceiling grid, DC power supply, and the required number of and location of lights, taking inrush into account.

The inrush prevention tool may be implemented as a computer program product stored on a computer-readable medium or downloadable from a network, which comprises code means for producing the steps of method claim 6 when run on a computing device.

Further advantageous embodiments are defined below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, based on embodiments with reference to the accompanying drawings, wherein:

Figs, la and lb show an office room before and after application of the proposed inrush prevention tool according to a first embodiment, respectively;

Figs. 2a and 2b show an office room before and after application of the proposed inrush prevention tool according to a second embodiment, respectively;

Figs. 3a and 3b show two office rooms before and after application of the proposed inrush prevention tool according to a third embodiment, respectively;

Figs. 4a and 4b show an office room before and after application of the proposed inrush prevention tool according to a fourth embodiment, respectively;

Figs. 5a and 5b show an office room before and after application of the proposed inrush prevention tool according to a fifth embodiment, respectively;

Figs. 6a and 6b show an office room before and after application of the proposed inrush prevention tool according to a sixth embodiment, respectively; and Figs. 7a and 7b show an office room before and after application of the proposed inrush prevention tool according to a seventh embodiment, respectively.

DESCRIPTION OF PREFERRED EMBODIMENTS

Various embodiments of the present invention will now be described based on a DC power distribution system of an office building.

Fig. la shows an exemplary office room 1 with six ceiling lights 10a, 10b organized in two, independently-controllable groups, one group on the window-side including window-sided lights 10a, the other group on a corridor-side including corridor- sided lights 10b. The lights of each group are coupled via a bus bar 20a, 20b respectively. It is assumed that an inrush problem will occur when the three lights of each group are simultaneously powered on, the respective bus bar 20a, 20b causing over-current condition; it is further assumed that placing two lights on one bus bar would not.

As shown in Fig. lb, according to a first embodiment, by limiting the number of lights (especially in this example, two lights) per bus bar 20a, 20b, 20c and changing the orientation of some bus bars 20a, the inrush problem can be solved, as each group of lights associated with one bus bar 20a, 20b, 20c cannot cause an over-current condition any more. In this specific embodiment, each bus bar 20a, 20b, 20c supplies power to only two lights.

Fig. 2a shows an exemplary office room 1 according with six ceiling lights 10a, 10b organized in two, independently-controllable groups, one group consisting of window-sided lights 10a, the other group consisting of corridor-sided lights 10b. It is assumed that an inrush problem will occur when two or three lights of each group are simultaneously powered on, the respective bus bar 20a, 20b will create inrush current causing over-current condition; it is further assumed that placing two lights of which only one is switched at a given moment (especially, when light is required at a window side or when light is required at a corridor side) would not cause over-current condition.

As shown in Fig. 2b, to a second embodiment, by changing the orientation of the bus bars 20a, 20b, 20c, there are only two lamps 10a, 10b per bar, and the lamps belong to different groups, such that only one of them is typically being switched at a given moment.

Fig. 3a shows two exemplary office rooms la, lb each with six ceiling lights 10a, 10b organized in one group respectively, independently-controllable groups, one group consisting of window-sided lights 10a and corridor-sided lights 10b. It is assumed that an inrush problem will occur when six lights on one bus bar 20a, 20b are simultaneously powered on, the respective bus bar 20a, 20b will create inrush current causing over-current condition; it is further assumed that placing six lights of which only three are switched at a given moment (especially, when light is required at a window side or when light is required at a corridor side) would not cause over-current condition.

As shown in Fig. 3b, according to a third embodiment, by allowing the bus bars 20a, 20b to be used by lamps 10a, 10b in different groups (in two neighbour groups), two neighbouring rooms share lamps 10a, 10b on joint bus bars. It is unlikely that both presence detectors in different, especially adjacent rooms la, lb lead to a reaction exactly at the same time. This means that when an office is entered, three lamps 10a, 10b on the first bus bar 20a and three lamps 10a, 10b on the second bus bar 20b are switched on, but not six lights on a single bar. The bars could be directly connected or crossed. Crossing is beneficial when the corridor-/window-side lamps can have different operational points, e.g. based on the input of a daylight sensor.

Fig. 4a shows an exemplary office room 1 with six ceiling lights 10a, 10b organized in two independently-controllable groups, one group consisting of window-sided lights 10a and corridor-sided lights 10b. It is assumed that an inrush problem will occur when the three lights of each group are simultaneously powered on, the respective bus bar 20a, 20b causing over-current condition; it is further assumed that placing two lights on one bus bar would not.

As shown in Fig. 4b, according to a fourth embodiment, by distributing the lights of one group over an external bus bar 20el, 20e2 and an internal bus bar 20il, 20i2, each external bus bar 20el, 20e2 supplies power for two lights lOel, 10e2 and each external bus bar 20il, 20i2 supplies power for one light lOil, 10i2.

Fig. 5a shows an exemplary office room 1 with six ceiling lights 10a, 10b organized in two independently-controllable groups, one group consisting of window-sided lights 10a and corridor-sided lights 10b. It is assumed that an inrush problem will occur when the three lights of each group are simultaneously powered on, the respective bus bar 20a, 20b will cause over-current condition; it is further assumed that placing two lights on one bus bar would not.

As shown in Fig. 5b, according to a fifth embodiment, by physically increasing the density of the bus bars 20a, 20b, 20c, 20d and changing the location of the luminaires 10a, 10b, luminaires of one group can be distributed across several bus bars.

Fig. 6a shows an exemplary office room 1 with six ceiling lights 10a, 10b organized in two independently-controllable groups, one group consisting of window-sided lights 10a and corridor-sided lights 10b. It is assumed that an inrush problem will occur when the three lights of each group are simultaneously powered on, the respective bus bar 20a, 20b will cause over-current condition; it is further assumed that placing two lights on one bus bar would not.

As shown in Fig. 6b, according to a sixth embodiment, by physically increasing the density of the bus bars 20a, 20b, 20c, 20d (i.e. exchange a passive bar by a powered bus bar) and changing orientation of the luminaires, e.g. if the connectors are integrated into bus bar housing turning them by 180deg, such that the connector is attached to the other bus bar; if the connectors are attached to the luminaire via cable, the connector can be attached to another bus bar, such that luminaires of one group are distributed across bus bars. In particular, bus bar 20d supplies power for luminaire 10b3; bus bar 20c supplies power for luminaires lObl, 10b2; bus bar 20a supplies power for luminaires lOal, 10a2; and bus bar 20b supplies power for luminaire 10a3.

Fig. 7a shows an exemplary office room 1 with six ceiling lights 10a, 10b organized in two independently-controllable groups, one group consisting of window-sided lights 10a and corridor-sided lights 10b. It is assumed that an inrush problem will occur when the three lights of each group are simultaneously powered on, the respective bus bar 20a, 20b will cause over-current condition.

As shown in Fig. 7b, according to a seventh embodiment, by assigning the lamps of one group to two sub-groups lOal, 10a2, lObl, 10b2, and the sub-groups being activated with slight delay, inrush currents will disappear. The sub-groups activated with slight delay is acceptable from the application (user) point of view, but allowing the inrush currents to disappear.

The proposed process performed by the inrush prevention tool can be run iteratively, with design criteria changed by the user or allowing for incorporating some design changes manually made by the user.

The inrush prevention tool functionality as described above is envisaged for the phase of designing/planning the DC installation. This functionality, as part of the same or different tool, can be used for installation assistance, installation check and

maintenance, debugging, installation. The functionality may be implemented as a software routine running on a computer device.

In summary, the present invention relates to design- and installation-time tool for solving the inrush problem. The proposed design and planning tool for DC power distribution networks takes into account the inrush behavior of the loads and distributes the loads likely to be switched on at the same time (e.g. being members of one control group) to different bus bars.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein. In particular, other variable energy conversion mechanisms may be provided within the switch device, and other geometries or arrangements of the moving device may provide for a compact and efficient switch device.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. An apparatus for inrush mitigation in power distribution system, said apparatus being adapted to analyze inrush behavior of loads of said power distribution system and to output an installation information such that predetermined power limitations are met when power is switched on.

2. The apparatus according to claim 1, wherein said apparatus is adapted to assign loads to bus bars depending on their power characteristics, intended control behavior and/or location.

3. The apparatus according to claim 1, wherein said apparatus is adapted to assign loads in a same control group to different bus bars.

4. The apparatus according to claim 1, wherein said apparatus is adapted to split a control group into sub-groups, controlled with a delay.

5. The apparatus according to claim 1, wherein said apparatus is adapted to provide information about at least one of a change of orientation of bus bars, an increased density of bus bars, an increased number of bus bars, and a shortening of bus bars.

6. A method for inrush mitigation in power distribution system, said method comprising analyzing inrush behavior of loads of said power distribution system and outputting an installation information such that predetermined power limitations are met when power is switched on.

7. A computer program product comprising code means for producing the steps of method claim 6 when run on a computing device.