Elevator call distribution in elevator system

Abstract

According to an aspect, a method for elevator call allocation in an elevator system is provided. The method includes receiving, from each of a plurality of elevator cars of the elevator system, charge information associated with an energy storage of the elevator car; receiving an elevator call of a floor providing a charging device for the energy store; an elevator call is assigned to an elevator car of the plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars.

Description

[0001] This application is a divisional application of the invention patent application with application date of March 5, 2020, application number 202010146208.X, and invention name “Elevator call allocation in elevator system”. Background Art

[0002] A moving cableless elevator car needs to have on-board energy storage to supply power to the elevator car. These energy storages have a limited energy storage capacity, so it is necessary to recharge them at sufficient intervals. Insufficient charge in the energy storage system can lead to an interruption of the power supply for car electrification in the worst case, which can lead to an emergency stop in the case of a wirelessly operated elevator car.

[0003] In addition, on-board energy storage using battery technology (e.g., configurations of individual battery cells connected in series and parallel) has an inherent problem of imbalance between individual cell voltages due to differences in cell resistance throughout the battery pack. This means that the battery pack must be balanced at some point after the cell voltages differ too far from each other. Severe cell imbalance reduces the usable capacity of the battery pack and, in the worst case, leads to the risk of overcharging or discharging.

[0004] Therefore, a solution is needed that will maintain the charge of the energy storage of the elevator cars during operation of the elevator system while still maintaining an acceptable service level. Summary of the invention

[0005] According to at least some aspects, a solution is provided that prevents an onboard energy storage of an elevator car from negatively impacting traffic handling performance in an elevator system due to a low charge level or battery imbalance in the energy storage. The disclosed solution assigns a received elevator call to an elevator car among a plurality of elevator cars based at least in part on charge information associated with an energy storage received from each of the plurality of elevator cars.

[0006] According to a first aspect, a method for elevator call distribution in an elevator system is provided. The method includes receiving charge information associated with an energy storage device of an elevator car from each of a plurality of elevator cars of the elevator system; receiving an elevator call to a floor where a charging device for the energy storage device is provided; and allocating the elevator call to an elevator car among a plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars. A solution is provided that enables charging of the energy storage devices of the elevator cars while still maintaining an adequate service level in the elevator system. The disclosed solution may also prevent the on-board energy storage devices from negatively impacting traffic handling performance due to unintentional low charge levels or battery imbalances in the energy storage devices. Additionally, the solution may also enable better performance of the energy storage devices in terms of efficiency, safety, and lifetime because they may be operated within an optimal operating range.

[0007] In one embodiment, the charge information includes a request to charge the energy storage device.

[0008] In one embodiment, the charge information includes a request to perform cell balancing of the energy storage.

[0009] In one embodiment, the charge information includes at least one of a charge level of an energy storage device of each elevator car and a battery imbalance.

[0010] In one embodiment, the method further comprises determining that a charge level of an energy storage device of an elevator car is below a first threshold level; determining that a received elevator call is associated with a landing floor having a charging device for charging the energy storage device of the elevator car; and assigning the elevator call to an elevator car having a charge level below the first threshold level to enable charging of the elevator energy storage device at the landing floor.

[0011] In one embodiment, the method further includes determining that the charge level of the energy storage of the elevator car is below a second threshold level; taking the elevator car out of service; and controlling the elevator car to travel to a landing floor having a charging device to charge the energy storage of the elevator car.

[0012] In one embodiment, the method further comprises determining that a battery imbalance of an energy storage device of the elevator car exceeds a third threshold; taking the elevator car out of service; and controlling the elevator car to travel to a landing floor having a charging device to balance the energy storage device of the elevator car.

[0013] According to a second aspect, an elevator group controller is provided, comprising means for receiving, from each of a plurality of elevator cars of an elevator system, charge information associated with an energy storage device of the elevator car; means for receiving an elevator call to a floor where a charging device for the energy storage device is provided; and means for allocating the elevator call to an elevator car of the plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars.

[0014] In one embodiment, the charge information includes a request to charge the energy storage device.

[0015] In one embodiment, the charge information includes a request to perform cell balancing of the energy storage.

[0016] In one embodiment, the charge information includes at least one of a charge level of an energy storage device of each elevator car and a battery imbalance.

[0017] In one embodiment, the elevator group controller further comprises means for determining that the charge level of the energy storage device of the elevator car is below a first threshold level; means for determining that a received elevator call is associated with a landing floor having a charging device for charging the energy storage device of the elevator car; and means for assigning the elevator call to an elevator car having a charge level below the first threshold level so as to enable charging of the elevator energy storage device at the landing floor.

[0018] In one embodiment, the elevator group controller also includes a device for determining that the charge level of the energy storage device of the elevator car is lower than a second threshold level; a device for removing the elevator car from service; and a device for controlling the elevator car to travel to a landing floor having a charging device to charge the energy storage device of the elevator car.

[0019] In one embodiment, the elevator group controller further comprises means for determining that a battery imbalance of an energy storage device of an elevator car exceeds a third threshold; means for removing the elevator car from service; and means for controlling the elevator car to travel to a landing floor having a charging device to balance the energy storage device of the elevator car.

[0020] According to a third aspect, there is provided an elevator system comprising the elevator group controller of the second aspect.

[0021] In one embodiment, the elevator system comprises at least two elevator shafts, each of the at least two elevator shafts comprising a plurality of landings and at least one charging device for charging an energy store of an elevator car, wherein the charging devices of different elevator shafts are arranged at different floors.

[0022] According to a fourth aspect, there is provided a computer program comprising program code which, when executed by at least one processing unit, causes the at least one processing unit to perform the method according to the first aspect.

[0023] According to a fifth aspect, there is provided a computer readable medium comprising program code which, when executed by at least one processor, causes the at least one processor to perform a method according to any first aspect.

[0024] According to a sixth aspect, an apparatus is provided. The apparatus includes a processor configured to receive charge information associated with an energy storage of an elevator car from each of a plurality of elevator cars of an elevator system, receive an elevator call to a floor where a charging device for the energy storage is provided, and assign the elevator call to an elevator car of the plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars.

[0025] The apparatus discussed above may be implemented, for example, using at least one processor, at least one processor and at least one memory connected to at least one processor, or at least one processor, at least one memory connected to at least one processor, and an input / output interface connected to at least one processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are included to provide a further understanding of the present invention and constitute a part of this specification, illustrate embodiments of the present invention and, together with the description, are used to explain the principles of the present invention. In the drawings:

[0027] Figure 1A A flow chart of elevator call distribution according to one embodiment is shown.

[0028] Figure 1B A flow chart of elevator call distribution according to another embodiment is shown.

[0029] Figure 1C A flow chart of elevator call distribution according to another embodiment is shown.

[0030] Figure 1D A flow chart of elevator call distribution according to another embodiment is shown.

[0031] Figure 2 A block diagram of an elevator system according to one embodiment is shown.

[0032] Figure 3 A charging device in an elevator system according to one embodiment is shown.

[0033] Figure 4 A graph depicting the charge level of an energy storage according to one embodiment is shown.

[0034] Figure 5 A block diagram of an elevator group controller according to one embodiment is shown. DETAILED DESCRIPTION

[0035] The following description shows a solution that prevents an on-board energy storage of an elevator car of an elevator system from negatively affecting traffic handling performance in the elevator system due to a low charge level or battery imbalance in the energy storage. The disclosed solution can use, for example, charge state information associated with the energy storage as a parameter when assigning elevator calls to the elevator cars.

[0036] The state of an energy storage device is mainly characterized by its charge level and cell imbalance. The term "charge level" as used herein refers to the available charge at a specific moment relative to the total capacity of the energy storage device. The term "cell imbalance" refers to the difference in charge level between the individual cells of the energy storage device.

[0037] Figure 1A A flow chart of elevator call allocation according to one embodiment is shown. The method shown can be performed, for example, by an elevator group controller of an elevator system. The method can be implemented as a computer-implemented method.

[0038] At 100, charge information associated with an energy storage device of an elevator car is received from each of a plurality of elevator cars of an elevator system. Each elevator car includes an energy storage device that provides power to various devices of the elevator car (e.g., lights, operating panels, etc.). In some embodiments, the charge information includes at least one of a charge level and a battery imbalance of the energy storage device of each elevator car. Each elevator may have an associated elevator controller, and the associated elevator controller may be connected to an elevator group controller. In other embodiments, the charge information may include a request to charge the energy storage device or a request to perform battery balancing of the energy storage device.

[0039] At 102, an elevator call is received at a floor where a charging device for an energy storage device is provided. One or more floors in a building may be provided with a charging device. The term "charging device" means that when the elevator car is fixed at a specific floor, the energy storage device of the elevator car can be charged, for example by using a wireless or wired charging solution. The elevator call may be caused by a passenger calling by pressing an up / down button at the floor. Alternatively, the elevator call may be caused by a passenger making a destination call, and the passenger or passengers making the call are immediately signaled that an elevator is being served.

[0040] At 104, an elevator call is assigned to an elevator car among the plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars. This provides a solution that enables charging of energy storage devices of elevator cars while still maintaining adequate service levels in the elevator system. The disclosed solution may also prevent onboard energy storage devices from negatively impacting traffic handling performance due to unintentional low charge levels or battery imbalances in the energy storage devices. Additionally, the solution may also enable better performance of the energy storage devices in terms of efficiency, safety, and lifespan because they may be operated within an optimal operating range.

[0041] When the charge information includes a request to charge the energy storage or to perform battery balancing of the energy storage, the energy storage system in the elevator car can have a battery management unit that can determine the battery balance and / or charge state. The energy storage system can then generate a battery balancing or charging request for the elevator group controller when necessary. The elevator group controller then assigns the appropriate call to the elevator to service the request (or can take the elevator out of service to perform battery balancing, etc.).

[0042] Figure 1B A flow chart of elevator call allocation according to one embodiment is shown. The method shown can be performed, for example, by an elevator group controller of an elevator system. The method can be implemented as a computer-implemented method. Figure 1A Steps 100 and 102 have been discussed in the description of FIG.

[0043] At 106, it is determined that the charge level of the energy storage is below a first threshold level but above a second threshold level. The first threshold level may refer to a lower value of an optimal operating range of charge levels. The first threshold may be set, for example, to 50% of a full charge of the energy storage.

[0044] At 108, an elevator call is assigned to an elevator car having a charge level below a first threshold but above a second threshold in order to charge an energy storage of the elevator car.

[0045] Figure 1C A flow chart of elevator call allocation according to one embodiment is shown. The method shown can be performed, for example, by an elevator group controller of an elevator system. The method can be implemented as a computer-implemented method. Figure 1A Steps 100 and 102 have been discussed in the description of FIG.

[0046] At 110, it is determined that the charge level of the energy storage of the elevator car is below a second threshold. This may mean that the charge level of the energy storage is too low for the optimal operating range of the charge level. This means that the charge level is considered too low to maintain adequate safety and performance characteristics.

[0047] At 112, the elevator car is taken out of service.

[0048] At 114, the elevator car is controlled to travel to a landing floor having a charging device to charge the energy storage of the elevator car. This ensures that the elevator car will restore a sufficient charge level for its energy storage.

[0049] Figure 1D A flow chart of elevator call allocation according to one embodiment is shown. The method shown can be performed, for example, by an elevator group controller of an elevator system. The method can be implemented as a computer-implemented method. Figure 1A Steps 100 and 102 have been discussed in the description of FIG.

[0050] At 116, it is determined that the cell imbalance of the energy storage exceeds a third threshold. When the cells of the energy storage are rebalanced, they may also be charged to a full 100% charge level. Severe cell imbalance may reduce the available capacity of the energy storage, leading to a risk of overcharging or discharging in the worst case. Therefore, it is important to perform cell balancing at intervals sufficient to maintain cell balance. In some embodiments, cell balancing may be performed, for example, once a day.

[0051] At 118, the elevator car is taken out of service.

[0052] At 120, the elevator car is controlled to travel to a landing floor having a charging device to charge the energy storage of the elevator car. This ensures that the elevator car will restore a sufficient charge level for its energy storage.

[0053] Figure 2 A block diagram of an elevator system 200 is shown according to one embodiment. Figure 2 The elevator system 200 can be configured to implement Figure 1A , any of the methods discussed in 1B, 1C or 1D.

[0054] The elevator group controller 200 can control a plurality of elevator controllers 202A, 202B, 202C, 202D. Each elevator controller 202A, 202B, 202C, 202D can control its associated elevator car. Each elevator car includes an energy storage 204 that provides power to various devices of the elevator car (e.g., lights, operating panel, etc.). The energy storage 204 has two characteristics that reflect its operating capabilities, namely, a charge level 206 and a battery imbalance 208. The charge level 206 represents the available charge 206 at a particular moment relative to the total capacity of the energy storage. The battery imbalance 208 represents the difference in charge level between the individual batteries of the energy storage 204. The elevator group controller 200 can periodically receive status updates of the energy storage 204 from the elevator controller 202B or directly from the energy storage 204. In some embodiments, the elevator group controller 200 can receive a request from the energy storage 204 to charge the energy storage 204.

[0055] Due to the difference in cell resistance across the battery pack, on-board energy storage using battery technology (e.g., configurations of individual battery cells connected in series and parallel) has an inherent problem of imbalance between individual battery cell voltages. This means that the battery pack must be balanced at some point after the cell voltages have become too far apart from each other. Severe cell imbalance reduces the usable capacity of the battery pack and, in the worst case, leads to the risk of overcharging or discharging.

[0056] One or more floors in a building may be provided with a charging device to charge the energy storage of the elevator car. The elevator shaft may include the main part of the charging device, and the elevator car may include the secondary part of the charging device. When the elevator car is stationary on the floor where the charging device is provided, the charging can be realized, for example, as wireless charging or as a contact-based solution.

[0057] The elevator group controller 200 receives an elevator call for a floor providing charging means for the energy storage. The elevator group controller 200 assigns the elevator call to one of the plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars.

[0058] In some embodiments, the elevator group controller 200 determines that the charge level 206 of the energy storage 204 is below a first threshold level. The first threshold level can be set to any level that still maintains the operation of the elevator car within a predetermined time period. As an example, the first threshold level can be set to 55% of the full charge of the energy storage 204. When the elevator group controller 200 determines that the received elevator call is associated with a landing floor having a charging device for charging the energy storage of the elevator car, the elevator group controller 200 can assign the elevator call to the elevator car with a charge level below the first threshold level so that the elevator energy storage can be charged at the landing floor.

[0059] In some embodiments, the elevator group controller 200 determines that the charge level of the energy storage 204 is below a second threshold level. Typically, the second threshold level is less than the first threshold level. As an example, when the first threshold level may be set to 55% of the full charge of the energy storage 204, the second threshold level may be set to 50%. If the charge level of the energy storage 204 is below the second threshold level, the elevator group controller 200 may take the elevator car out of service and control the elevator car to travel to a landing floor with a charging device to charge the energy storage 204.

[0060] Certain battery technologies (e.g., lithium-ion batteries) may have better safety, performance, and life characteristics when operating within an optimal operating range of charge levels. For example, the optimal operating range may be set to 50%-70%. By keeping the charge level of the energy storage 204 between the optimal operating ranges, this allows the energy storage system to have better performance in terms of efficiency, safety, and life.

[0061] In some embodiments, the elevator group controller 200 determines that the battery imbalance 208 of the energy storage 204 crosses a third threshold. The battery imbalance 208 may reduce the available capacity of the energy storage 204, and in the worst case may lead to the risk of overcharging or discharging. Therefore, in some embodiments, when the battery imbalance 208 of the energy storage 204 crosses the third threshold, the elevator group controller 200 may stop the elevator car from service and control the elevator car to travel to a landing floor with a charging device to balance the energy storage 204.

[0062] Furthermore, when assigning elevator calls to elevator cars, the elevator group controller 200 may also take into account that the charging of the energy storage 204 may be constrained by the available output power from the charging device and the ability of the energy storage 204 to receive that power. For example, in battery balancing, the current may be very small, and balancing a heavy, unbalanced battery pack may take a long time.

[0063] In real-world building traffic conditions, it may be that charging opportunities are not evenly distributed among the various elevator cars in the elevator group, but rather that some on-board energy storage devices have lower charge levels than other energy storage devices. Variations in charge levels within an elevator group may be caused by, for example, an uneven number of stops at one or more charging levels, uneven stop times at charging levels, or uneven power consumption between different elevator cars. The elevator group controller 200 may be configured to control the charging of the energy storage devices of the elevator cars to minimize the need to take the elevators out of service.

[0064] Figure 3 A charging device in an elevator system according to one embodiment is shown. Figure 3 The example shown depicts a building with nine floors 300-316 and six elevator shafts. Each floor 300-316 is served by six elevators 308A-308F. Two of the floors 300, 316 are equipped with charging devices. In other words, when an elevator stops at one of the floors 300, 316, it can charge its energy storage device there. Figure 3 An example is shown in which all elevator shafts share the same charging level 300, 316, in other embodiments the number of charging levels may vary between different elevator shafts. Figure 3 An example with nine layers is shown, in other embodiments the number of layers may be less than nine layers or greater than nine layers.

[0065] like Figure 3 As shown, the elevator system may include at least two elevator shafts, each of the at least two elevator shafts including a plurality of landings and at least one charging device for charging the energy storage device of the elevator car, wherein the charging devices of different elevator shafts are arranged at different floors. This increases the allocation options, since trips with different destination floors can be allocated as energy storage charging trips.

[0066] Figure 4 A graph depicting the charge level of an energy storage device according to one embodiment is shown. Figure 3 In the example shown, the optimal operating range of the energy storage devices 206A-206F of the elevator car is considered to be 50% to 70% of the full charge of the energy storage devices (i.e., the lower threshold is 50% and the upper threshold is 70%). Figure 3As can be seen, the charge levels 206A, 206B, 206D, 206E, 206F are within the set optimal operating range. However, the charge level 206C is below the set lower threshold level. In one embodiment, for this reason, elevator calls to floors where charging devices are provided can be assigned to elevator cars including energy storage devices with charge levels below the set lower threshold. In another embodiment, elevator cars including energy storage devices with charge levels below the set lower threshold can be taken out of service and controlled to travel to a landing floor with a charging device to charge the energy storage device.

[0067] In some embodiments, the number of threshold levels may be one or more than two.In one embodiment, the elevator group controller may emphasize assignments differently based on the charge level of the energy storage (where an elevator service call is associated with a charging floor).

[0068] Figure 5 A block diagram of an elevator group controller 200 according to one embodiment is shown. The elevator group controller 200 shown may include a controller or processor 502 (e.g., a signal processor, a microprocessor, an ASIC, or other control and processing logic circuit) for performing tasks such as signal encoding, data processing, input / output processing, power control, and / or other functions. The elevator group controller 200 shown may include one or more memories 504. The memory 504 may include non-removable memory and / or removable memory. The non-removable memory may include RAM, ROM, flash memory, a hard disk, or other well-known memory storage technologies. The memory 304 may also be used to store data and / or code for running one or more application programs.

[0069] The elevator group controller 200 may further include a data interface 506 that enables communication with an external device or network. The data interface 506 may include a wired or wireless transceiver for communicating with an external device or network. The components of the elevator group controller 200 are exemplary, and the elevator group controller 200 may also include other components or elements.

[0070] The memory 504 may include a computer program that, when executed by the processor 502, causes the elevator group controller 200 to receive charge information associated with an energy storage device of an elevator car from each of a plurality of elevator cars of the elevator system; receive an elevator call to a floor where a charging device for the energy storage device is provided; and assign the elevator call to an elevator car among the plurality of elevator cars based at least in part on the charge information received from each of the plurality of elevator cars.

[0071] also, Figure 5Any combination of the components shown disclosed in the foregoing, for example, at least one of the processor 502, the memory 504, and the data interface 506 may constitute a device for determining that a charge level of an energy storage device of an elevator car is below a first threshold level; a device for determining that a received elevator call is associated with a landing floor having a charging device for charging the energy storage device of the elevator car; and a device for assigning the elevator call to an elevator car having a charge level below the threshold level to enable charging of the elevator energy storage device at the landing floor.

[0072] The example embodiments may be implemented with software, hardware, application logic, or a combination of software, hardware, and application logic. The example embodiments may also store information related to the various methods described herein. The information may be stored in one or more memories, such as a hard disk, an optical disk, a magneto-optical disk, a RAM, etc. One or more databases may store information for implementing the example embodiments. The database may be organized using data structures (e.g., records, tables, arrays, fields, graphs, trees, lists, etc.) included in one or more memories or storage devices listed here. The methods described with respect to the example embodiments may include appropriate data structures for storing data collected and / or generated by the methods of the devices and subsystems of the example embodiments in one or more databases.

[0073] All or part of the example embodiments may be conveniently implemented using one or more general purpose processors, microprocessors, digital signal processors, microcontrollers, etc. programmed according to the teachings of the example embodiments, as will be understood by those skilled in the art in the computer and / or software fields. As will be understood by those skilled in the software field, based on the teachings of the example embodiments, programmers of ordinary skill can easily prepare appropriate software. In addition, as will be understood by those skilled in the electrical field, the example embodiments may be implemented by preparing a dedicated integrated circuit or by an appropriate network interconnecting conventional component circuits. Therefore, the example is not limited to any particular combination of hardware and / or software. Stored on any one or combination of computer-readable media, the example may include software for controlling components of the example embodiments, for driving components of the example embodiments, for enabling components of the example embodiments to interact with human users, and the like. Such computer-readable media may also include a computer program for executing all or part of the processing performed in implementing the example embodiments (if the processing is distributed). The computer code means of the example may include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, and the like. In the context of this document, a "computer-readable medium" can be any medium or device that can contain, store, communicate, propagate, or transmit instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. Computer-readable media can include computer-readable storage media, which can be any medium or device that can contain or store instructions for use by or in connection with an instruction execution system, apparatus, or device (such as a computer). Computer-readable media can include any suitable medium that participates in providing instructions to a processor for execution. Such media can take a variety of forms, including but not limited to non-volatile media, volatile media, transmission media, etc.

[0074] Although the basic novel features as applied to the preferred embodiments thereof have been shown and described and pointed out, it should be understood that various omissions and substitutions and changes in the form and details of the described apparatus and methods may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and / or method steps that perform substantially the same function in substantially the same manner to achieve the same results are within the scope of the present disclosure. In addition, it should be recognized that the structures and / or elements and / or method steps shown and / or described in conjunction with any disclosed form may be incorporated into any other disclosed or described or suggested form or embodiment as a general matter of design choice. In addition, in the claims, the device-plus-function clause is intended to cover the structures described herein that perform the functions described, and includes not only structural equivalents, but also equivalent structures.

[0075] According to the common knowledge of those skilled in the art, the applicant separately discloses each individual feature described herein and any combination of two or more such features, to the extent that these features or combinations can be performed based on this specification as a whole, regardless of whether these features or combinations of features solve any problems disclosed herein, and without limiting the scope of the claims. The applicant points out that the disclosed aspects / embodiments may include any such individual features or combinations of features. In view of the foregoing description, it is obvious to those skilled in the art that various modifications can be made within the scope of the present disclosure.

Claims

1. A method for elevator call distribution in an elevator system, the method comprising: receiving, from each of a plurality of elevator cars of the elevator system, charge information associated with an energy storage of the elevator car, wherein the charge information includes at least a charge level of the energy storage of each elevator car; receiving an elevator call initiated by a passenger for a floor where a charging device for an energy storage device is provided; determining that a charge level of an energy storage device of the elevator car is below a first threshold level; determining that the received elevator call is associated with a landing floor having a charging device for charging an energy storage device of the elevator car; and An elevator call is assigned to an elevator car having a charge level below a first threshold level for charging the elevator energy storage at said landing floor.

2. A method for elevator call distribution in an elevator system, the method comprising: receiving, from each of a plurality of elevator cars of the elevator system, charge information associated with an energy storage device of the elevator car, wherein the charge information includes at least a battery imbalance of the energy storage device of each elevator car; receiving an elevator call for a floor where charging means for the energy storage device are provided; determining that a battery imbalance of an energy storage device of the elevator car exceeds a third threshold; Taking the elevator car out of service; and The elevator car is controlled to travel to a landing floor with a charging device to balance the energy storage device of the elevator car.

3. An elevator group controller, comprising: means for receiving, from each of a plurality of elevator cars of the elevator system, charge information associated with an energy storage of the elevator car, wherein the charge information includes at least a charge level of the energy storage of each elevator car; means for receiving an elevator call for a floor where charging means for an energy storage device are provided; means for determining that a charge level of an energy storage device of the elevator car is below a first threshold level; means for determining that a received elevator call is associated with a landing floor having a charging device for charging an energy storage device of the elevator car; and Means for allocating an elevator call to an elevator car with a charge level below a threshold level for charging an elevator energy storage device at said landing floor.

4. An elevator group controller, comprising: means for receiving, from each of a plurality of elevator cars of the elevator system, charge information associated with an energy storage device of the elevator car, wherein the charge information includes at least a battery imbalance of the energy storage device of each elevator car; means for receiving an elevator call for a floor where charging means for an energy storage device are provided; means for determining that a battery imbalance of an energy storage device of the elevator car exceeds a third threshold; means for taking the elevator car out of service; and The elevator car is controlled to travel to a landing floor with a charging device to balance the energy storage device of the elevator car.

5. An elevator system comprising an elevator group controller according to any one of claims 3-4.

6. The elevator system according to claim 5 comprises at least two elevator shafts, each of the at least two elevator shafts comprising a plurality of landings and at least one charging device for charging an energy storage device of an elevator car, wherein the charging devices of different elevator shafts are arranged on different floors.

7. A computer program comprising program code which, when executed by at least one processor (402), causes the at least one processor (402) to perform the method according to any one of claims 1-2.

8. A computer readable medium comprising program code which, when executed by at least one processor (402), causes the at least one processor (402) to perform the method according to any one of claims 1-2.

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