WO2012137092A1

WO2012137092A1 - Device and method for dynamic load control in lighting systems

Info

Publication number: WO2012137092A1
Application number: PCT/IB2012/051390
Authority: WO
Inventors: Ying Wang; Sri Andari Husen; Ludovicus Marinus Gerardus Maria Tolhuizen; Meng Zhao
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-04-04
Filing date: 2012-03-23
Publication date: 2012-10-11

Abstract

Present invention provides controlling power consumption of at least one group of plurality of groups of lighting devices, each group comprising change range indicating values, by which energy consumption of the respective group can be changed. To this, for each of the at least one group a corresponding target power consumption change value is determined, by which power consumption of the corresponding group has to be changed, by selecting for each group of the plurality of groups a corresponding target power consumption change value from the corresponding change range of the corresponding group such that normalized illumination change values of the plurality of groups have minimal difference among each other, each of the normalized illumination change values being determined for corresponding group by use of the selected target power consumption change value of the group.

Description

Device and method for dynamic load control in lighting systems

FIELD OF THE INVENTION

The invention relates to dynamic load control in lighting systems. Particularly, the invention refers to a device configured to control power consumption of at least one group of a plurality of groups of lighting devices and to a corresponding method.

Additionally, the present invention relates to a system comprising the device and to a computer program product comprising code configured for producing the steps of the method when run on a device configured for executing the computer program product.

BACKGROUND OF THE INVENTION

Lighting systems are known to consume a large proportion of energy or power in buildings and, more generally, in city infrastructures and may be seen as cause for high energy or power consumption. Therefore, lighting systems are often configured as controllable loads to offer dynamic load control services such as demand response in smart grids. By implementing lighting systems as controllable loads, by control of which it is ensured that the consumed electrical load or power consumption is less than what can be generated and/or provided, load reductions from lighting systems become more predictable and substantial and can be achieved within a short period of time.

In current lighting systems, lamps or lighting devices are often uniformly and simultaneously dimmed by use of dimmable ballasts for a period of time. Thereto, simple power line broadcasting mechanisms may be used for controlling (dimming) the lamps or lighting devices of the lighting systems.

When performing dynamic load control in smart grids, the amount of electricity generated and transmitted by the electricity grid must match at any time the electricity consumed by loads at the other end of the grid to ensure stability of the electricity grid. In known control systems, this is mainly achieved by adjusting the electricity generation to match the actual consumption. However, in several periods of time (e.g., during hot summer days), the electricity demand exceeds the generation capacity (e.g., due to intensive operating of air conditioning systems). Curtailment is then deployed to ensure that the grid can still deliver power generated under the available generation capacity. Usually, curtailment is done by the grid operator by manually disconnecting a distribution branch of the grid, deeming all loads served by the branch unusable during the curtailment period. Alternatively, grid customers can selectively and individually disconnect some loads from the grid. However, coordination and agreement between the grid customers and the grid operators on factors like the amount and duration of reduction, for example, is required. This necessitates reliable communication means between the grid operator and the customers. Furthermore, incentives and settlements may be needed to reward the customers. Hence, this approach is applicable only to a handful of large utility customers, typically, large industrial customers, which can supply a significant amount of reduction.

Due to the recent rapid developments in the area of communications technology, it is possible to connect a vast number of customers to the grid operator to deploy an orchestrated load shedding. Also economically, it has become more feasible to develop such infrastructure as the gap between the available generation and peak demand widens, driving up electricity or power costs. Currently, a number of demand response programs are operational in various states of the USA (e.g. California, Texas, New York), supplying reduction of the peak demand. Demand response will play an even more important role in the future Smart Grid to balance an increasingly dynamic grid due to growing integration of highly variable renewable energy or power resources.

On the facility level, participation in the demand response program requires actively controlling the load to ensure meeting the targeted demand reduction. Active load control may also benefit facilities not taking part in the demand response program as it can reduce the total cost of the consumed electricity or power. For instance, many utility companies charge the rate based on the peak power consumption during the billing period rather than the average power consumption. Proper control of peak demand may reduce costs of electricity consumption incurred by user(s). Active load control may also be used to take advantage of dynamic tariff pricing.

However, the known control systems fail to provide an energy consumption control, by use of which the control is performed with regard to whole lighting system by taking into consideration disturbing effects arising when controlling energy consumption and changing the energy consumption, i.e., the lighting levels of the lighting devices. Such disturbing effects may relate, for example, to wild changes in illumination levels in at least some of areas of the whole lighting system. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a methodology for improved controlling power consumption in a lighting system, i.e., for improved controlling lighting levels of devices of the lighting system with regard to power consumption allowed or targeted in the system. The power consumption control comprises power consumption reduction or shedding, respectively, and/or power consumption increasing or restoring, respectively.

The object is achieved by the features of the independent claims.

Herewith, a dynamic load shedding and/or restoring approach for lighting systems is provided to satisfy a target power consumption requested by grid or detected with regard to a certain state of the lighting system like a state of constantly decreasing or increasing amount of available energy or power amount, for example. To this, according to the present invention, optimal changes of power consumption levels for multiple service areas in the lighting system are designed or determined by taking into consideration for different individual service areas different illumination requirements, different load shedding and/or restoring flexibilities, different power-to-illumination efficiencies and/or disturbances due to changes in illumination levels, for example.

The invention is based on the idea of formulation of the above-outlined design of load shedding and/or restoring as a constrained optimization problem so that it can be solved by standard techniques like quadratic programming (QP), for example, what enables a fast and effective implementing of the present invention. As a result, an optimal distributing the disturbance is achieved due to load shedding and/or restoring performed according to the present invention over all service areas such that power and illumination constraints of individual service areas are satisfied or met. By translating the load shedding and/or restoring design to a constraint optimization problem, it becomes possible to extend the design to incorporate other constraints, for example, user specified priorities for different service areas, perceived comfort and/or disturbance based on more illumination parameters like color temperature, contrast etc. Thus, an efficient, flexible and extendable implementation of the present invention is enabled. In following, the individual service areas of the lighting system correspond to groups of lighting devices divided in the lighting system.

In one aspect of the present invention, a device is provided, which is configured to control power consumption of at least one group of a plurality of groups of lighting devices, each group of the plurality of groups comprising a change range, said change range indicating values, by which energy consumption of the respective group can be changed, wherein the device is configured to determine for each of the at least one group of the plurality of groups a corresponding target power consumption change value, by which power consumption of the corresponding group has to be changed, selecting for each group of the plurality of groups a corresponding target power consumption change value from the corresponding change range of the corresponding group such that normalized illumination change values of the plurality of groups have a minimal difference among each other, each of the normalized illumination change values being determined for a corresponding group by use of the selected target power consumption change value of the group.

By use of the present invention, a flexible and effective power consumption control is provided, which at the same time takes into consideration the degrees of illumination level changes in the whole system and ensures that a smooth illumination level changes are performed without causing disturbing effects, i.e., without having negative impacts with regard to comfort of consumers. The power consumption changes and, thus, illumination level changes are distributed in an appropriate way over the lighting system such that the disturbing effects are avoided. Further, several areas of the lighting system are handled individually by taking into consideration the conditions in said areas like the preferred or permitted change ranges, indicating values, by which energy consumption of the respective areas may or should be changed. The groups may comprise different numbers of lighting devices. In this way, the degree of individual handling of devices can be set flexibly, wherein, if a group comprises one lighting device only, a very high degree of individual handling is implemented with regard to said group and wherein an increasing number of lighting devices in a group leads to a lower degree of individual handling. Particularly, the present invention allows a well quantifying of disturbance and allows changes of illumination levels, which do not impact comfort of users.

According to an embodiment of the present invention, the device is configured to select for each group of the plurality of groups the corresponding target power

consumption change value such that a sum of the selected target power consumption change values is less than or equal a total power consumption change value, by which power consumption has to be changed among the plurality of groups of lighting devices. In this way, it is ensured that the targeted power consumption is actually achieved after adjusting the power consumption.

According to an embodiment of the present invention, the device is configured to determine the total power consumption change value in response to a request message requesting a power consumption change of the lighting devices or in response to a detection of a state, which indicates a requirement of a change of power consumption among the plurality of groups of lighting devices. In this way, a flexible implementing of the present invention is enabled. Further, it is ensured that the power consumption control and adjusting is performed when a need for changing the power consumption is actually present in the system.

According to an embodiment of the present invention, the device is configured to determine for each group the corresponding normalized illumination change value by dividing a coefficient of the group by a current illumination level value of the group and by multiplying a result of the dividing with the corresponding selected target power

consumption change value of the group, wherein the coefficient of the group is a coefficient used for determining an illumination change value of the group. In this way, an easy and fast implementation of the present invention is supported.

According to an embodiment of the present invention, the illumination change value of the group is determined by multiplying the target power consumption change value of the group with the coefficient of the group. In this way, an easy and fast implementation of the present invention is supported.

According to an embodiment of the present invention, the device is configured to determine the difference between the normalized illumination change values of the plurality of groups by use of a cost function. In this way an optimal, effective and fast quantifying of the difference of changes of lighting levels in the system is enabled.

consumption change value by determining a solution for an optimization problem. Thus, the present invention allows a well quantifying of disturbance by the optimization problem to be solved and allows changes of illumination levels, which do not impact comfort of users.

According to an embodiment of the present invention, the device is configured to determine the solution for an optimization problem by use of an implementation of a quadratic programming method. In this way, a fast and efficient determining of a solution of the optimization problem becomes possible.

According to an embodiment of the present invention, for each group of the plurality of groups the corresponding change range is determined by a load shedding flexibility value of the group and a load restoring flexibility value of the group, wherein the load shedding flexibility value of the group indicates a maximum amount of power, by which power consumption of lighting devices of the group can be reduced at a current time such that a minimum power consumption permissible in the group at the current time is maintained, and wherein the load restoring flexibility value of the group indicates a maximum amount of power, by which the power consumption of the lighting devices of the group can be increased at the current time such that a maximum power consumption permissible in the group at the current time is maintained. In this way, an individual handling of current state in the groups of illumination devices is supported.

According to an embodiment of the present invention, a minimum value of the change range of the group is the load shedding flexibility value multiplied by -1 and wherein a maximum value of the change range of the group is the load restoring flexibility value. In this way, a fast and effective implementing of the present invention is supported. According to an embodiment, the range may be divided in a range for power consumption shedding and in a range for power consumption restoration. In this case, the minimum value of the power consumption shedding range of the group is the load shedding flexibility value of the group multiplied by -1 and the maximum value of the power consumption shedding range of the group is zero. Further, the maximum value of the power consumption restoration range of the group is the load restoring flexibility value of the group and the minimum value of the power consumption restoration range of the group is zero.

According to an embodiment of the present invention, the device is configured to initiate in each of the at least one group a corresponding power consumption change process, wherein in said corresponding process the power consumption of the corresponding group is changed by the corresponding determined target power consumption change value. In this way, a fast and effective implementing of the present invention is supported.

According to an embodiment of the present invention, for each of the at least one group of the plurality of groups the corresponding target power consumption change value is determined such that in each of the at least one group a new power consumption value of the corresponding group is set to a value obtained by a sum of the corresponding determined target power consumption change value of the group and a current power consumption value of the group.

In one aspect of the present invention, a method for controlling power consumption of at least one group of a plurality of groups of lighting devices is provided, each group of the plurality of groups comprising a change range, said change range indicating values, by which energy consumption of the respective group can be changed, wherein the method comprises determining for each of the at least one group of the plurality of groups a corresponding target power consumption change value, by which power consumption of the corresponding group has to be changed, by selecting for each group of the plurality of groups a corresponding target power consumption change value from the corresponding change range of the corresponding group such that normalized illumination change values of the plurality of groups have a minimal difference among each other , each of the normalized illumination change values being determined for a corresponding group by use of the selected target power consumption change value of the group. Also by the method, the advantages and effects of the present invention as provided in the present description are achieved.

According to an embodiment of the present invention, the method is performed by a device, which is configured to control power consumption of at least one group of a plurality of groups of lighting devices. The device corresponds to the above outlined device, which is described in more detail below.

In a further aspect of the present invention, a system comprising a device configured to control power consumption of at least one group of a plurality of groups of lighting devices is provided. The device corresponds to the above outlined device, which is described in more detail below.

In another aspect of the present invention, a computer program product is provided, which comprises code configured for producing the steps of method, as outlined above and described in more detail below, when run on a device configured for executing the computer program product. The device may correspond to the above outlined device being described in more detail below.

In this way, an efficient, effective, flexible, extendable power consumption control is enabled, which takes into consideration different requirements set out with regard to both the lighting system as whole and specific parts of the lighting system. Said requirements refer, for example, to different illumination requirements, different load or power consumption shedding and/or restoring flexibilities, different power-to-illumination efficiencies, disturbances due to changes in illumination levels etc. The power consumption control may be implemented by utilizing different degrees of individual handling of service areas of the lighting system. With the power consumption control according to the present invention disturbing effects like wild changes in illumination levels for some service areas, for example, are avoided. The present invention provides a design of an optimal load or power consumption shedding and/or restoring method for fairly distributing the disturbance over multiple service areas, which also takes into account the current power consumption and illumination levels when a new power consumption target is received or detected. The approach of the present invention can be implemented in a fast and flexible way without wasting system resources by considering the current power consumption and actually allowed or permitted power consumption at a given situation or given point of time with high accuracy and in an optimal way.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 illustrates an exemplary environment where the present invention can be implemented;

Fig. 2 illustrates a lighting system according to an embodiment of the present invention;

Fig. 3 illustrates a lighting system according to a further embodiment of the present invention;

Fig. 4 illustrates an exemplary power consumption profile for load shed/restore in a system comprising four groups of lighting devices according to an embodiment of the present invention;

Fig. 5 illustrates steps for determining for each of a plurality of groups a corresponding target power consumption change value, by which power consumption of the corresponding group has to be changed, according to an embodiment of the present invention; and

Fig. 6 illustrates an arrangement of a device configured to control power consumption of at least one group of a plurality of groups of lighting devices according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 illustrates an exemplary environment where the present invention can be implemented. Particularly, Fig. 1 illustrates a plan of a building that is sub-divided into different areas like corridor 16, workspace 11, 12, 13, 14 and reception 15, for example, that serve different purposes. A lighting system, comprising a plurality of lighting devices or energy consuming devices in general, is implemented in the several areas 11 - 16. Each functional area 11 - 16 may have different illumination requirements. Further, each functional area 11 - 16 may have a different flexibility towards load shedding, i.e. powering down the load or illumination level reduction. For example, some areas like the corridor 16, for example, may tolerate illumination reduction up to 50% while other areas like the workspace 11, 12, 13, 14 or reception 15, for example, may tolerate illumination reduction up to 20% only.

According to the present embodiment, the lighting system may comprise controllable and non-controllable loads, i.e. lighting devices, energy or load consumption of which can be controlled for ensuring that the load or energy consumed by the system is less than what can be generated or provided, and lighting devices, energy of load consumption of which can not be controlled. In following, for the ease of description, a lighting system with controllable loads, i.e. with controllable lighting devices will be considered, wherein it has to be noted that the present invention can be applied also to a system comprising additionally non-controllable loads or lighting devices.

According to the present embodiment, the lighting devices of the lighting system are grouped into K groups (K > 0 (e.g., K≥2)), each of said groups consisting of one or more controllable loads or lighting devices respectively. According to an embodiment, lighting devices of a group may serve an area like the corridor 16, office room 11 - 14 or reception 15, for example. In general, the present invention allows different assignments of lighting devices to the K groups.

Further, each of the K groups has at least one lighting device, wherein it is possible that at least one of the K groups comprises one lighting device only. In this way, the level of accuracy of controlling lighting devices may be adjusted, wherein, if at least one of the groups comprises one or view lighting devices, the accuracy level for controlling the at least one group may be high and wherein, if at least one of the groups comprises many lighting devices, the accuracy level may be correspondingly lower. In this way, a flexible implementation of control of lighting devices is allowed.

Fig. 2 illustrates a lighting system according to an embodiment of the present invention, where the system comprises lighting devices 212, 222, 232 divided exemplary into three groups 21, 22, 23. Further, according to the present embodiment, each group 21, 22, 23 has a controller 211, 221, 231, referred in following to also as group controller, each of the group controllers 211, 221, 231 being configured for controlling the energy consumption and, thus, also illumination levels of the corresponding lighting devices 212, 222, 232 belonging to the corresponding group 21, 22, 23 of the respective group controller 211, 221, 231. The illumination levels and, thus, the energy consumption levels for the lighting devices 212, 222, 232 are determined according to the present embodiment by taking into account information like occupancy status (e.g., derived by at least one occupancy sensor), daylight levels (e.g., derived from a daylight sensor), tasks performed in the area (e.g., obtained from user input), for example. Illumination levels of the lighting devices 212, 222, 232 can be determined, for example, as being lower during the daytime than in the morning or evening.

Further, according to the present embodiment, the system comprises a central controller 20, which controls the power consumption of the lighting devices of the system. The central controller 20 can control the power or energy consumption of the system by performing corresponding communications with the group controllers 211, 221, 231, as indicated by the arrows between the central controller 20 and the group controllers 211, 221, 231 in Fig. 2. Moreover, the system may comprise an electricity power sensing unit measuring the power consumption of the system. The several sensor units like the above mentioned occupancy sensors, daylight sensors or the power sensing unit are visualized exemplary by components 24 in Fig. 2 for simplifying the representation of the system, wherein it is clear that different arrangements of different sensor units 24 with regard to their locations in the system are possible according to the present invention. Additionally, according to the present embodiment, the system comprises communications means like communications network or system, for example, for information exchange between controllers 20, 211, 221, 231, sensors 24 and the lighting devices 212, 222, 232. The corresponding communications means is outlined exemplary in Fig. 2 by different arrows between the corresponding components, wherein several ways of communications (also such not shown) can be implemented according to the present invention.

The groups 21, 22, 23 may be divided such that each group corresponds to an area like corridor 16, workspace 11, 12, 13, 14 and reception 15, for example. In general, the present invention allows several different ways of dividing the lighting devices 212, 222, 232 into appropriate groups 21, 22, 23, as already outlined above.

According to the present embodiment, the central controller 20 corresponds to the above outlined device configured to control power consumption of at least one group 21, 22, 23 of a plurality of groups of lighting sources or devices 212, 222, 232. According to the present embodiment, the central controller 20 controls power consumption of all groups 21, 22, 23. The operating of the central controller 20 with regard to power consumption control is explained exemplary in more detail below.

Fig. 3 illustrates a lighting system according to an embodiment of the present invention. In comparison to Fig. 2, where a system with a centralized architecture is established, the system of Fig. 3 comprises a distributed architecture. According to the distributed architecture of Fig. 3, no central controller 20 is provided. Further, in line with the present embodiment, each group controller 31 , 32, 33 performs in addition to tasks performed also by group controllers 211, 221, 231 of Fig. 2 also tasks of a central controller like the central controller 20 of Fig. 2. This decentralized architecture implies also changes in the communications network utilized in the system, where each group controller 31 , 32, 33 is configured to communicate with each other group controller 31 , 32, 33. Further, each group controller 31, 32, 33 is configured to communicate with corresponding occupancy sensors, daylight sensors or the power sensing units visualized exemplary by components 24. In general, according to the present embodiment, the configuration of the group controllers 31 , 32, 33 corresponds to configuration of group controllers 211, 221, 231 and to configuration of central controller 20, wherein instead of communicating with the central controller 20 the group controllers 31, 32, 33 communicate accordingly among each other. The dividing of groups 21, 22, 23 is performed according to the present embodiment in the same way as described exemplary above with regard to Figs. 1 and 2.

Further, according to the present embodiment, each of the group controllers 31, 32, 33 correspond to the above outlined device configured to control power consumption of at least one group 21, 22, 23 of a plurality of groups of lighting sources or devices 212, 222, 232. According to the present embodiment, each of the group controllers 31, 32, 33 controls power consumption of its corresponding group 21, 22, 23. The operating of the group controllers 31, 32, 33 with regard to power consumption control is explained in more detail below.

Before explaining the power consumption control, as performed according to the present invention, in more detail, the following symbols or parameters respectively used for the power consumption control are introduced in following with regard to K groups 21, 22, 23 indicated by index k = Ι,.,.,Κ .

I_k represents a value of a current illumination level of the k-th group 21, 22,

23.

P_k represents a value of a current power consumption of the k-th group 21, 22,

23.

P_k ^mm represents a value of a minimum power consumption of the k-th group 21, 22, 23 acceptable or permissible in said group 21, 22, 23.

P_k ^msK represents a value of a maximum power consumption of the k-th group

21, 22, 23 acceptable or permissible in said group 21, 22, 23.

G represents a value of target total power consumption desired or to be adjusted in the system of lighting devices 212, 222, 232, which, for example, may be requested by the grid or may be determined with regard to detecting a situation indicating that a power consumption change has to be performed in the system.

P_k ^ew represents a value of a new power consumption of the k-th group 21, 22,

23 after performing a power consumption change in said group 21, 22, 23. The power consumption change may be a shedding or reducing of the power consumption in said group 21, 22, 23 or may be restoring or increasing of the power consumption in said group 21, 22, 23.

Each of the above listed parameters may be time-varying, i.e. may correspond to a certain time instance t , wherein in many embodiments the time instance t may correspond to the current time. Thus, the parameters can be also annotated as follows: I_k (t) ,

P_k it) , P_k ^min (t) , (t) , G(t) , P_k ^new(t) . For notational simplicity, mentioning the time index t is omitted in the following description. However, it is pointed out, that the steps or operations may be performed with regard to a certain time instance t , which may correspond to the current time.

Additionally, it should be taken into consideration that a system comprising lighting devices 212, 222, 232 representing controllable loads may comprise lighting devices being non-controllable loads, i.e., lighting devices power consumption and, thus, illumination levels of which can not be adjusted or controlled (e.g. by dimming). The power consumption of the lighting devices being non-controllable loads is referred to as P_non . In cases, where the system comprises non-controllable loads, the target total power consumption value G may be set by subtracting the power consumption of the non-controllable loads P_non from the original target total power consumption value G , i.e. G := G - P_non .

According to some embodiments of the present invention, the value P_k ^new of new power consumption of the k-th group 21, 22, 23 may be such that a sum of new power consumption values P_k ^ew of each of groups 21, 22, 23 is less than or equal the total power

K

consumption value G , i.e.,∑P_k"^ew≤ G . Further, according to some embodiments of the k=l

present invention, the value P_k ^ew of new power consumption of the k-th group 21, 22, 23 may be such that it is a value from a range defined by the value P_k ^mm of minimum power consumption of the k-th group 21, 22, 23 (as minimum value of the range) and the value P_k ^msK of a maximum power consumption of the k-th group 21, 22, 23, i.e., P_k ^new e [P_k ^mia ,P_k ^msK ] . Furthermore, according to some embodiments, P_k"^ew should satisfy both of said constraints:

K

∑ nnew rtnew - min max

< G , and ^> e |i^> ,i^> J . (1)

For the k-th group 21, 22, 23, the change of power consumption to be performed in said k-th group 21, 22, 23 or target power consumption change value respectively is denoted by δ_λ , the load shedding flexibility value is denoted by LSF_k , the load restoring flexibility value is denoted by LRF_k and the change of illumination level or illumination change value respectively is denoted by δ_{7 k} . Also these values or parameters may be time- varying, i.e. may correspond to a certain time instance t , wherein in many embodiments the time instance t may correspond to the current time.

Said values or parameters may be defined with regard to the k-th group 21, 22,

23 as follows: s - . (2)

δ^ = βΑ > β, > 0 · (5)

A positive value may indicate a power increase or restoration, a negative value δ^ may indicate power reduction or shedding. LSF_k and LRF_k may be non-negative, i.e. greater than or equal to zero or positive values, respectively. The change of illumination level δ_{7 k} may be proportional to the change of power consumption δ^ with a coefficient , which may be specific for the k-th group 21, 22, 23. A larger may indicate a more efficient light source or group 21, 22, 23, i.e., a large variation of illumination level only needs a small variation of power. Further, in line with some embodiments of the present invention, the following two assumptions may be made: 1) for each light source or lighting device 212, 222, 232, the change of illumination level is linearly related to the change of power consumption level, and 2) each group 21, 22, 23 comprises at least one or one lighting device 212, 222, 232. The first assumption is widely recognized for various types of dimmable lighting devices 212, 222, 232. The second assumption is made for simplifying the description and should not be considering as limiting the present invention and embodiments of the present invention. A group 21, 22, 23 contains multiple light sources or lighting devices 212, 222, 232 with same or similar power-to-illumination efficiency, i.e., same or similar values of the coefficients

According to some embodiments, from constraints concerning P_k ^new , given by (1) exemplary, corresponding constraints on may be defined as:

£δ,≤Δ <md S_k c [- LSF_k ,LRF_k ] (6) k=l

K

where Δ = G - P_k .

k=l

Here, with Δ a total power consumption change value is denoted, by which power consumption has to be changed among the plurality of groups 21, 22, 23 of lighting devices 212, 222, 232 in the system.

In general, constraints of (1) correspond to constraints of (6). Thus, when seeking for a solution of an optimization problem such that constraints of (6) are met the solution found meets also constraints of (1) and vice versa - when seeking for a solution of an optimization problem such that constraints of (1) are met the solution found meets also constraints of (6).

Fig. 4 illustrates an exemplary power consumption profile for load shed/restore in a system comprising four groups of lighting devices according to an embodiment of the present invention. According to the present embodiment K = 4 and k = 1,...,4 . Fig. 4a shows exemplary bounds for current power consumption P_k of each k-th group and Fig. 4b shows exemplary bounds for target power consumption change value of each k-th group. The bounds may be set in different ways. Thus, the bound values may be predefined values defined with regard to a specific time item(s) t and/or with regard to specific (predefined) states of the system.

Fig. 5 illustrates steps for determining for each of a plurality of groups 21, 22, 23 a corresponding target power consumption change value, by which power consumption of the corresponding group 21, 22, 23 has to be changed, according to an embodiment of the present invention when controlling power consumption of at least one group 21, 22, 23 of the plurality of groups 21, 22, 23 of lighting devices 212, 222, 232. The steps of Fig. 5 may be performed, for example, by the central controller 20 of Fig. 2 when a centralized architecture is utilized or by group controllers 31, 32, 33 of Fig. 3 when a distributed architecture is utilized. In the following, the device 20, 31, 32, 33 performing the steps of Fig. 5 is referred to as device 20, 31, 32, 33 controlling power consumption of at least one group 21, 22, 23.

According to the present embodiment, a total power consumption change value Δ is determined in step S51 by the device 20, 31, 32, 33 controlling power

consumption of at least one group 21, 22, 23.

Step S51 may be performed in response to a request message requesting a power consumption change of the lighting devices 212, 222, 232 and received by the device 20, 31, 32, 33 controlling power consumption of at least one group 21, 22, 23 from an utility or a further component of the (electrical) grid being an interconnected network for delivering electricity from suppliers to consumers. The request message may comprise information allowing determining S51 of the total power consumption change value Δ like G , for example. The total power consumption change value Δ is determined by the above-described

K

equation A = G - P_k .

k=l

Here, it has to be pointed out that, if the system comprises also non- controllable loads with their total power consumption P_non , as described above, the total power consumption change value Δ is determined in step S51 by use of an adapted target total power consumption G being derived as follows: G := G - P_non . After determining the adapted target total power consumption G , if non-controllable loads are comprised in the

K

system, the calculation of the equation Δ = G - P_k is performed by use of the adapted k=l

target total power consumption G .

Further, step S51 may be performed also in response to a detection of a state, which indicates a requirement of a change of power consumption among the plurality of groups of lighting devices. The total power consumption change value Δ is determined S51 as described above also in this case, wherein the target total power consumption G is determined based on the detected state.

In step S52, a solution for an optimization problem is computed (by the device 20, 31, 32, 33 controlling power consumption of at least one group 21, 22, 23) for

determining for each of the at least one group 21, 22, 24 of the plurality of groups 21, 22, 21 a corresponding target power consumption change value , by which power consumption of the corresponding k-th group 21, 22, 23 has to be changed to achieve the total power consumption change Δ . The objective of the optimization problem is to minimize the difference of disturbance among the K groups 21, 22, 23 when changing power consumption in the system, i.e., when changing illumination levels of the lighting devices 212, 222, 232 in the system.

To this, the disturbance is quantified. The disturbance of the k-th group 21, 22, 23 can be, for example, the change of power consumption or, correspondingly, the change of illumination level δ_{7 k} . The absolute change of illumination level may not reflect the perceived comfort by the user. Considering, for example, δ_{7 k} = 50 lux , changing from 1000 lux to 950 lux may not be noticeable, while changing from 100 lux to 50 lux may be very disturbing. Therefore, it makes sense to normalize the change of illumination level as percentage of the current illumination level:

¾ = δ,_* /'* = (β_*/Ά, (7) wherein x_k is a normalized illumination change value of the k-th group 21, 22,

23.

Further, the difference among the normalized illumination change values x_k of all K groups 21, 22, 23 is quantified. To this, given a vector x = [x_l x₂ ... χ_κ ]^τ (^T denoting the transpose operator), the difference among its entries x_k , the normalized illumination change values of the K groups 21, 22, 23, can be measured or determined by use of a cost function J as:

^(x^ - x) , where x = l/K

k=l

where I_K is an KxK identity matrix and A_j is an KxK matrix containing all one's, i.e.

1 0 0 0 0 1 1 1 1 ··

0 1 0 0 0 1 1 1 1 ··

0 0 1 0 0 1 1 1 1 ··

and A,

0 0 0 1 1 1 1 1

0

0 0 0 0 0 1 1 1 1 1 1

and where II...11 specifies a vector norm, i.e., if v is a vector or matrix v v.

By use of the aforesaid, according to the present embodiment, the best or optimal target power consumption change value of the k-th group 21, 22, 23 is determined by formulating a constrained optimization problem with inputs Δ and LSF_k ,

LRF_k , _k/I_k for all K groups 21, 22, 23 as follows:

argmin (l^-K^A^ (9)

O] for load shedding

wherein 1^τδ < Δ and δ, e

[O, LRF^ for load restoring where δ =[δ_ι δ₂...δ^]^τ is a Kxl vector, wherein 1 is a vector containing Ί ' as elements, and D is a KxK diagonal matrix with the k-th diagonal element being

0 ... 0 β,/7 0 κ 0

0 κ 0 β /

χ_ι 0 ... 0

0 χ₂ 0 :

: 0 ^' · . 0 ^'

0 ... 0 χ_ν

The output of the optimization problem as provided above is for all K groups 21, 22, 23.

The solution of equation (9) specifying the optimization problem according to the present embodiment can be obtained by use of a quadratic programming (QP) approach, e.g. the active-set method as described, for example, in P.E. Gill, W. Murray, M.A. Saunders, and M.H. Wright "Procedures for Optimization Problems with a Mixture of Bounds and General Linear Constraints", ACM Trans. Math. Software, vol. 10, pp. 282-298, 1984.

Thus, in general, the step S52 comprises selecting δ^ e [- LSF_k , LRF_k ] for all

K groups 21, 22, 23 in step S521, determining x_k by use of selected δ^ for all K groups 21,

22, 23 in step S522 and determining the difference among all x_k ( k = 1, ... , K ) by use of the cost function J in step S523. The solution of the optimization problem as specified according to the present embodiment by equation (9) is found or determined when the lowest or minimal difference among all x_k ( k = 1, ... , K ) is determined. As result of determining

S52 the solution for an optimization problem, in step S53 the selected values δ_: , δ₂ , ... , δ^ are provided, by use of which the lowest or minimal difference among all x_k (k = 1, K ) has been determined.

Intuitively, it does not make sense to increase power consumption for one group and decrease power consumption for another one. However, it can be mathematically shown that this indeed is the case. As a result, the optimization can be carried out under the restriction e [- LSF_k , θ] in case of load shedding, and under the restriction e [θ, LRF_k ] in case of load restoration. Thus, in case of load shedding (restoration), only the load shedding (load restoration) flexibilities need to be known and signaled.

Also, it can mathematically be shown that there exists an optimal solution for which 1^τδ = Δ .

This may further simplify the implementation of an optimization algorithm.

Subsequently, in step S54, the device 20, 31, 32, 33, controlling power consumption of at least one group 21, 22, 23, initiates a power consumption change process in the corresponding at least one group 21, 22, 23 by use of the corresponding value representing the solution of the optimizing problem, wherein the change of illumination level δ_{7 k} in the k-th group 21, 22, 23 may be determined as δ_{7 k} = _kd_k , wherein the new illumination level I_k ^ew of the k-th group 21, 22, 23 may be determined as I_k ^ew = I_k + I_kx_k , wherein the new power consumption P_k ^new of the k-th group 21, 22, 23 may be determined as p^new _ p^ _|_5^ _ device 20, 31, 32, 33, controlling power consumption of at least one group 21, 22, 23, may initiate S54 the power consumption change process by transmitting at least one of the values δ^ , δ_{7 k} , I_k ^ew , P_k ^ew to the corresponding at least one group 21, 22, 23 or by adjusting the devices 212, 222, 232 of the at least one group 21, 22, 23 by use of at least one of the values δ, , δ₇ , , I_k ^new , P_k ^new .

Particularly, if the device is a central controller 20, the central controller 20 will transmit at least one of the values δ^ , δ_{7 k} , I_k ^ew , P_k ^ew to the corresponding group controllers 211, 221, 231 for adjusting the power consumption in the corresponding groups 21, 22, 23 by the corresponding group controllers 211, 221, 231. If the device is a group controller 31, 32, 33 in a system with a distributed architecture, the corresponding group controller 31 , 32, 33 will adjust the corresponding devices 212, 222, 232 of the at least one group 21, 22, 23 by use of at least one of the values δ^ , 8_IJc , I_k ^new , P_k ^new .

The adjusting may comprise a power consumption increase (or restoration) or reduction (or shedding), i.e. illumination level increase (or restoration) or reduction (or shedding), wherein the increase or restoration, respectively, is indicated by positive values δ^ , δ_{7 k} and the reduction or shedding, respectively, is indicated by negative values δ^ , δ_{7 k} . Table provided below represents an exemplary calculation of a device 20, 31,

32, 33 controlling power consumption of at least one group, where the target total power consumption G in the system is 350 W and where four groups are provided or divided in the system (i.e., K = 4 ):

The optimized power consumption change results in a normalized illumination level change x_k as equal as possible among the four groups, meanwhile satisfying all the power constraints of different groups. As shown in the above-provided table, groups 1, 2 and 4 reduce their illumination level by approximately 17% each, while group 3 reduces its illumination level by 13.7% and just reaches its P™^m of 92 W.

In another embodiment, an approximate solving of an optimization algorithm is applied, that is easy to implement and yields a sub-optimal solution. In following, the approximate solving is described with regard to load shedding, wherein for load restoration the algorithm is performed correspondingly in a similar way. At first, the power usage of all groups is reduced with an amount corresponding to the same value of all ¾ until either the system target power reduction is met, or a minimum power level for some group is attained. In the latter case, the reduction of the power consumption of the remaining groups is continued with an amount corresponding to the same value ¾ until the system power target is met or the minimum power level for another group is attained. This is continued until the target system power reduction has been achieved. When applying this approximate to the example of the above table, in a first iteration, the power consumption is changed in each group with the value corresponding to x=Xk = -24/175, i.e., the initial load reductions are (250/5)*x = -48/7 W for group 1, (1300/10)** = - (26*24)/35 W for group 2, -12W for group 3 and (300/3)*x = -96/7 W for group 4. It can be observed, that group 3 has reached its minimum power level and that the total power consumption change equals 50.4W, so a further power consumption reduction of 9.6 W is required. This is achieved by further changing the power consumption of groups 1,2 and 4 by an amount corresponding to y=Xk = -6/175. So overall, for £=1,2,4, we have that x_k= -24/175 + ( -6/175) = -30/175, while x₃ = - 24/175, resulting in power consumption changes 5_k = -8.57 W, -22.29 W, -12W, -17.14 W for k=l,2,3,4, respectively.

The value of the cost function J measuring the difference in the changes of the illumination values equals 0.000855 for the optimal solution, and 0.000882 for the approximate solution.

When performing the approximate solving with regard to load restoration, at first, the power usage of all groups is increased with an amount corresponding to the same value of all ¾ until either the system target power restoration is met, or a maximum power level for some group is attained. In the latter case, the restoration or increasing of the power consumption of the remaining groups is continued with an amount corresponding to the same value Xk, until the system power target is met or the maximum power level for another group is attained. This is continued until the target system power restoration or increase has been achieved.

Fig. 6 illustrates an arrangement of a device 6 configured to control power consumption of at least one group 21, 22, 23 of a plurality of groups 21, 22, 23 of lighting devices 212, 222, 232 according to an embodiment of the present invention. The device 6 may correspond to the central controller 20 of Fig. 2 or to group controllers 31, 32, 33 of Fig. 3. According to the present embodiment the device 6 comprises a computer program product 61, which comprises code 611 configured for performing the steps of the method of the present invention, as described exemplary above, when run on a the device 6. The device 6 is configured for executing the computer program product 61. According to the present embodiment, the structure of the device 6 is arranged or adapted such that it allows execution of the computer program product 61. The computer program product 61 may be incorporated in a correspondingly arranged hardware and/or software component arrangement 62 of the device 6.

Thus, present invention provides controlling power consumption of at least one group of plurality of groups of lighting devices, each group comprising change range indicating values, by which energy consumption of the respective group can be changed. To this, for each of the at least one group a corresponding target power consumption change value is determined, by which power consumption of the corresponding group has to be changed, by selecting for each group of the plurality of groups a corresponding target power consumption change value from the corresponding change range of the corresponding group such that normalized illumination change values of the plurality of groups have minimal difference among each other, each of the normalized illumination change values being determined for corresponding group by use of the selected target power consumption change value of the group.

It is obvious that the above-described embodiments can be combined in various ways. By means of the above described power consumption controlling, an efficient, effective, extendable power consumption control is provided, which enables an optimal and fail distributing the disturbances like wild changes in illumination levels, for example, over multiple service areas of the whole lighting system. Further, it ensures an optimal consideration of requirements in the service areas when adjusting power consumption in the lighting system.

Claims

CLAIMS:

1. A device (20, 31 , 32, 33, 6) configured to control power consumption of at least one group (21, 22, 23) of a plurality of groups (21, 22, 23) of lighting devices (212, 222, 232), each group (21, 22, 23) of the plurality of groups (21, 22, 23) comprising a change range, said change range indicating values, by which energy consumption of the respective group (21, 22, 23) can be changed, wherein the device (20, 31, 32, 33, 6) is configured to determine for each of the at least one group (21, 22, 23) of the plurality of groups (21, 22, 23) a corresponding target power consumption change value, by which power consumption of the corresponding group (21, 22, 23) has to be changed, by selecting for each group (21, 22, 23) of the plurality of groups (21, 22, 23) a corresponding target power consumption change value from the corresponding change range of the corresponding group (21, 22, 23) such that normalized illumination change values of the plurality of groups (21, 22, 23) have a minimal difference among each other, each of the normalized illumination change values being determined for a corresponding group (21, 22, 23) by use of the selected target power consumption change value of the group (21, 22, 23).

2. The device (20, 31, 32, 33, 6) according to claim 1, wherein the device (20, 31, 32, 33, 6) is configured to select for each group (21, 22, 23) of the plurality of groups (21, 22, 23) the corresponding target power consumption change value such that a sum of the selected target power consumption change values is less than or equal to a total power consumption change value, by which power consumption has to be changed among the plurality of groups (21, 22, 23) of lighting devices (212, 222, 232).

3. The device (20, 31, 32, 33, 6) according to claim 2, wherein the device (20, 31, 32, 33, 6) is configured to determine the total power consumption change value in response to a request message requesting a power consumption change of the lighting devices (212, 222, 232) or in response to a detection of a state, which indicates a requirement of a change of power consumption among the plurality of groups (21, 22, 23) of lighting devices (212, 222, 232).

4. The device (20, 31, 32, 33, 6) according to any one of the preceding claims, wherein the device (20, 31, 32, 33, 6) is configured to determine for each group (21, 22, 23) the corresponding normalized illumination change value by dividing a coefficient of the group (21, 22, 23) by a current illumination level value of the group (21, 22, 23) and by multiplying a result of the dividing with the corresponding selected target power

consumption change value of the group (21, 22, 23), wherein the coefficient of the group (21, 22, 23) is a coefficient used for determining an illumination change value of the group (21, 22, 23).

5. The device (20, 31, 32, 33, 6) according to claim 4, wherein the illumination change value of the group (21, 22, 23) is determined by multiplying the target power consumption change value of the group (21, 22, 23) with the coefficient of the group (21, 22, 23).

6. The device (20, 31, 32, 33, 6) according to any one of the preceding claims, wherein the device (20, 31, 32, 33, 6) is configured to determine the difference between the normalized illumination change values of the plurality of groups (21, 22, 23) by use of a cost function.

7. The device (20, 31, 32, 33, 6) according to any one of the preceding claims, wherein the device (20, 31, 32, 33, 6) is configured to select for each group (21, 22, 23) of the plurality of groups (21, 22, 23) the corresponding target power consumption change value by determining a solution for an optimization problem.

8. The device (20, 31, 32, 33, 6) according to claim 7, wherein the device (20, 31, 32, 33, 6) is configured to determine the solution for an optimization problem by use of an implementation of a quadratic programming method.

9. The device (20, 31, 32, 33, 6) according to any one of the preceding claims, wherein for each group (21, 22, 23) of the plurality of groups (21, 22, 23) the corresponding change range is determined by a load shedding flexibility value of the group (21, 22, 23) and a load restoring flexibility value of the group (21, 22, 23), wherein the load shedding flexibility value of the group (21, 22, 23) indicates a maximum amount of power, by which power consumption of lighting devices (212, 222, 232) of the group (21, 22, 23) can be reduced at a current time such that a minimum power consumption permissible in the group (21, 22, 23) at the current time is maintained, and wherein

the load restoring flexibility value of the group (21, 22, 23) indicates a maximum amount of power, by which the power consumption of lighting devices (212, 222, 232) of the group (21, 22, 23) can be increased at the current time such that a maximum power consumption permissible in the group (21, 22, 23) at the current time is maintained.

10. The device (20, 31, 32, 33, 6) according to claim 9, wherein a minimum value of the change range of the group (21, 22, 23) is the load shedding flexibility value multiplied by -1 and wherein a maximum value of the change range of the group (21, 22, 23) is the load restoring flexibility value.

11. The device (20, 31 , 32, 33, 6) according to any one of the preceding claims, wherein:

the device (20, 31 , 32, 33, 6) is configured to initiate in each of the at least one group (21, 22, 23) a corresponding power consumption change process, wherein in said corresponding process the power consumption of the corresponding group (21, 22, 23) is changed by the corresponding determined target power consumption change value.

12. The device (20, 31, 32, 33, 6) according to any one of the preceding claims, wherein for each of the at least one group (21, 22, 23) of the plurality of groups (21, 22, 23) the corresponding target power consumption change value is determined such that in each of the at least one group (21, 22, 23) a new power consumption value of the corresponding group (21, 22, 23) is set to a value obtained by a sum of the corresponding determined target power consumption change value of the group (21, 22, 23) and a current power consumption value of the group (21, 22, 23).

13. A method for controlling power consumption of at least one group (21, 22, 23) of a plurality of groups (21, 22, 23) of lighting devices (212, 222, 232), each group (21, 22, 23) of the plurality of groups (21, 22, 23) comprising a change range, said change range indicating values, by which energy consumption of the respective group (21, 22, 23) can be changed, wherein the method comprises determining for each of the at least one group (21, 22, 23) of the plurality of groups (21, 22, 23) a corresponding target power consumption change value, by which power consumption of the corresponding group (21, 22, 23) has to be changed, by selecting (S521) for each group (21, 22, 23) of the plurality of groups (21, 22, 23) a corresponding target power consumption change value from the corresponding change range of the corresponding group (21, 22, 23) such that normalized illumination change values of the plurality of groups (21, 22, 23) have a minimal difference among each other, each of the normalized illumination change values being determined (S522) for a

corresponding group (21, 22, 23) by use of the selected target power consumption change value of the group (21, 22, 23).

14. A system comprising a device (20, 31, 32, 33, 6) according to any one of claims 1 to 12.

15. A computer program product (61) comprising code (611) configured for producing the steps of method according to claim 12 when run on a device (20, 31, 32, 33, 6) configured for executing the computer program product (61).