CONTROLLER, SYSTEM AND METHOD FOR CONTROLLING THE STATE OF LIQUID CRYSTAL-BASED SWITCHABLE WINDOWS

Abstract

A method for controlling the state of two or more liquid crystal-based switchable windows includes in a first step providing correction data which define a relationship between a state signal and an output voltage level. The correction data is provided for each of the switchable windows and the state of the switchable windows may be adjusted according to the state signal between a minimum and maximum level. In a subsequent step, the state signal is provided which defines the desired state of one or more selected switchable windows. In a further step, a required voltage level is determined for setting the desired state based on the state signal and the respective correction data for each of the one or more selected windows. In a subsequent step d), an AC output voltage is generated having the required voltage level for each of the one or more selected windows.

Claims

1. A method for controlling the state of two or more liquid crystal-based switchable windows (30) comprising: a) providing correction data which defines a relationship between a state signal which defines the desired state and an output voltage level which defines the output voltage required to set the desired state, wherein the correction data is provided for each of the two or more switchable windows (30) and wherein the state of the switchable windows (30) may be adjusted according to the state signal between a minimum level and a maximum level, b) providing the state signal which defines the desired state of one or more selected windows of the two or more switchable windows (30), c) determining a required voltage level for setting the desired state based on the state signal and the respective correction data for each of the one or more selected windows, and d) generating an AC output voltage having the required voltage level for each of the one or more selected windows.

2. The method according to claim 1, wherein the state signal is provided as an analogue input signal or in form of a digital signal.

3. The method according to claim 1, wherein the state is a tint level which defines the transmission of visible light through the respective switchable window (30) or is a scattering level which defines the haze of the respective switchable window (30).

4. The method according to claim 3, wherein the state signal is provided in dependence on a received alarm signal, wherein in case an alarm signal indicating a fire alarm is received a state signal corresponding to a minimum tint level is provided for all switchable windows (30), in case an alarm signal indicating a rampage situation is received a state signal corresponding to a maximum tint level and/or a maximum haze level is provided for all switchable windows (30), and in case an alarm signal indicating a bird flying in close proximity to a switchable window (30) is received a state signal corresponding to maximum tint level and/or a maximum haze level for the respective switchable window (30) is provided.

5. The method according to claim 1, wherein the state signal is provided in dependence on one or more data sources selected from the group comprising interior photo sensors, exterior photo sensors, clocks, calendars, connections to communication devices, radar sensors, bird detection devices, interior temperature sensors, exterior temperature sensors, user input devices, noise sensors, room occupation sensors, power consumption sensors and historical climate databases.

6. The method according to claim 1, wherein the state signal is provided taking into account the position of the respective switchable window (30) in a façade of a building and a desired pattern.

7. The method according to claim 1, wherein the correction data is provided in form of parameters for a mathematical function and/or in form of a look-up table.

8. The method according to claim 1, wherein the provided correction data is selected such that the resulting output voltages cause each of the two or more switchable windows (30) to switch to essentially the same state for the same state signal.

9. The method according to claim 1, wherein phases of at least two AC output voltages are shifted with respect to each other.

10. The method according to claim 9, wherein AC output voltages for N of the two or more switchable windows (30) are provided, wherein the AC output voltage for the n-th window is phase shifted by an amount of (n−1)*(2π)/N for n from 1 to N.

11. The method according to claim 1, wherein the AC output voltage is a square wave AC voltage or a trapezoid wave AC voltage.

12. The method according to claim 1, wherein a charging current flows to the respective switchable window (30) for a rising edge of the AC output voltage and a discharge current flows from the respective switchable window (30) for a falling edge of the AC output voltage, characterized in that electrical energy is recuperated during the falling edge of the AC output voltage.

13. The method according to claim 8, wherein an output terminal for outputting the AC voltage is monitored for a DC offset and if a DC offset is detected, a DC bias of the AC output voltage is adjusted in order to control the DC offset at the output terminal to a target value of zero.

14. A controller (20) for controlling the state of two or more liquid crystal-based switchable windows (30) comprising a storage memory for storing correction data for each of the two or more switchable windows (30), an input port for receiving a state signal which defines the desired state of one or more selected windows of the two or more switchable windows (30), a processor configured to generate a driving signal for each of the switchable windows (30) in dependence on the state signal and the respective correction data and amplifiers for each of the two or more switchable windows (30) for amplifying the driving signal and for providing an AC output voltage for each of the switchable windows (30), wherein the controller (20) is configured to execute the method according to claim 1.

15. The controller (20) according to claim 14, wherein the amplifiers are configured as four quadrant buck converters and the controller additionally comprises a DC-buffer for storing recuperated energy.

16. A building management system (100) for controlling the state of two or more switchable windows (30) comprising one or more controllers (20) according to claim 14, a control unit (110) and a communication module (10), wherein the communication module (10) and the one or more controllers (20) are adapted to communicate by means of a first communication protocol and the communication module (10) is further adapted to communicate by means of a second communication protocol with the control unit (110).

17. A system comprising the building management system (100) according to claim 16 and two or more liquid crystal-based switchable windows (30), wherein the two or more liquid crystal-based switchable windows (30) are connected to the building management system (100).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The drawings show:

[0092] FIG. 1a a typical non-linear response of a transmission through a smart window in dependence on an analogue input signal,

[0093] FIG. 1b a linearized dependence of the transmission on the analogue input signal,

[0094] FIG. 2 an example of a building management system, and

[0095] FIG. 3 the control of the states of multiple smart windows by means of analogue input signals.

[0096] FIG. 1a depicts a diagram showing schematically a typical dependence of a transmission T.sub.vis of visible light through a smart window in dependence on a state signal in form of an analogue input signal V.sub.input. As can be seen from the diagram of FIG. 1a, the change of transmission in dependence on the analogue input signal V.sub.input is strongly non-linear. In a first part of the diagram, the transmission T.sub.vis is nearly constant and changes only slightly for changing input signal V.sub.input. In a second part of the diagram, T.sub.vis changes rapidly even for small changes in the input signal V.sub.input. Then, in a third part of the diagram, the transmission saturates and again changes only slightly for changing V.sub.input. This non-linear switching behavior is typical for liquid-crystal based switchable windows. The exact shape and in particular the required voltages for the maximum and minimum level of the transmission T.sub.vis are usually dependent on the specific liquid-crystal based switchable optical device of the windows and the size of the switchable optical device. Further, the required voltages may depend on further parameters such as the environmental conditions or the physical parameters of the switchable optical device may change over time due to aging.

[0097] In a typical application, the analogue input signal V.sub.input would be provided by means of a dimmer switch which is to be manually operated by a user. The strong non-linear response of the transmission T.sub.vis would be unexpected by the user and makes it difficult to set the transmission T.sub.vis to the desired value.

[0098] FIG. 1b depicts a diagram showing a linearized dependence of the transmission T.sub.vis of visible light through a smart window in dependence on the state signal in form of an analogue input signal V.sub.input. Such a linearization may be provided by applying the proposed method to determine the required output voltage for achieving the desired state in dependence on provided correction data and the analogue input signal V.sub.input. As can be seen from the diagram of FIG. 1b, the change of transmission in dependence on the analogue input signal V.sub.input is linear. Thus, the desired state of the transmission T.sub.vis may be easily set by means of, for example, a dimmer switch.

[0099] FIG. 2 shows a schematic view of a building management system 100 for controlling the state of a plurality of switchable windows 30. In the example depicted in FIG. 2, the building management system 100 controls the state of nine switchable windows 30.

[0100] In principle, the spatial arrangement of the switchable windows 30 relative to each other can be chosen as desired in the respective application, e.g. such as to form a façade of a building. In an embodiment the switchable windows 30 are arranged as a contiguous array, column or row. In another embodiment the switchable windows 30 are arranged in separate openings of a solid structure such as a wall.

[0101] Each of the switchable windows 30 has an electrical connection 32 for connecting the respective switchable windows 30 to a controller 20. By means of the electrical connection 32, the controller 20 provides an AC output voltage for driving of the respective switchable window 30. In the example shown in FIG. 2, the building management system 100 comprises three controllers 20, wherein each of the controllers 20 is configured for providing the AC output voltage for three switchable windows 30. In further embodiments, the controller 20 may be configured for a different number of switchable windows 30. For example, the controller 20 may be configured to provide the AC output voltage for 2 to 512 windows. Further, the building management system 100 may comprise a different number of controllers 20, for example from 1 to 64 controllers 20.

[0102] The three controllers 20 are interconnected by means of a first communication bus 12 and are configured to communicate by means of a first communication protocol. The first communication protocol may be, for example, RS485. The use of the first communication bus 12 allows coupling of several controllers 20 in order to expand the number of switchable windows 30 which may be connected to the building management system 100.

[0103] The controllers 20 are configured to provide the AC output voltage to the respective switchable windows 30 in dependence on state signals and correction data. In the building management system 100 of FIG. 2, a control unit 110 is used to provide the state signals.

[0104] The control unit 110 is configured to communicate by means of a second communication protocol which is, for example, the KNX protocol. For communicating with the controllers 20, the building management system 100 further comprises a communication module 10. The communication module 10 is adapted for communication using the first and the second communication protocol and is adapted to forward the state signals provided by the control unit 110 to the controllers 20. Accordingly, a second communication bus 22 connects the control unit 110 to the communication module 10 and the first communication bus 12 connects the communication module 10 to the controllers 20.

[0105] For controlling the state of all switchable windows 30 or of a selection of the switchable windows 30, the control unit 110 provides state signals for all or the selected ones of the switchable windows 30. These state signals may be prepared in dependence on external input or sensors which are connected to the control unit 110. The state signals are provided in form of a digital signal and are first sent using the second communication protocol over the second communication bus 22 to the communication module 10. The communication model 10 then translates the communication protocol and forwards the state signal to the respective controllers 20 using the first communication protocol over the first communication bus 12.

[0106] After receipt of the digital state signal by the respective controllers 20 a required voltage level for setting the desired state according to the state signal is determined based on the state signal and correction data. The correction data may, for example be stored in a non-volatile memory of the respective controller 20. Finally, the controllers 20 generate an AC output voltage for each of the selected switchable windows 30 according to the determined required voltage level.

[0107] FIG. 3 shows a second embodiment of the building management system 100 comprising a single controller 20 and three switchable windows 30 which are connected to the controller 20 using electrical connections 32. In the embodiment of FIG. 3, the state signals for defining the state of each of the three switchable windows 30 are provided in form of an analogue signal. The analogue signals are each provided using analogue input devices 24 which may, for example, be configured as dimmer switches.

[0108] After receipt of the analogue state signal by the controller 20 a required voltage level for setting the desired state according to the state signal is determined based on the state signal and correction data. The correction data may, for example be stored in a non-volatile memory of the controller 20. Finally, the controller 20 generates an AC output voltage for each of the selected switchable windows 30 according to the determined required voltage level.

WORKING EXAMPLES

[0109] Two liquid crystal-based switchable windows are prepared using ITO-coated glass substrates, a double cell configuration with cell gaps of 25 μm and a dye-doped liquid crystal medium which has a positive dielectric anisotropy. The first window, designated as W-A, has a size of 1 m×1 m. The second window, designated as W-B, has a size of 3 m×1 m.

[0110] Voltage is supplied to both windows via a driver for which respectively 11 values can be pre-set in a look-up table with a resolution range of 1000.

[0111] The transmission of light in the visible spectral range (T.sub.vis) is determined for both windows in dependence of the applied voltage. The transmission is normalized with respect to the darkest state (0% transmission) and the brightest state (100% transmission).

[0112] Table 1 shows the voltage-transmission behaviour for windows W-A and W-B at 20° C.

TABLE-US-00001 TABLE 1 T.sub.vis Voltage (V) for W-A Voltage (V) for W-B  0% 1.3 2.0 10% 1.6 2.2 20% 1.8 2.5 30% 2.0 2.8 40% 2.2 3.1 50% 2.5 3.5 60% 2.9 4.1 70% 3.5 4.9 80% 4.7 6.6 90% 7.2 10.0 100%  17.0 24.0

[0113] Based on these data a look-up table is compiled to apply the same voltage-transmission response for both windows for T.sub.vis increments between 0% and 100%. Considering the driver's output resolution of 1000 and the maximum applied voltage of 24 V as used for W-B at T.sub.vis of 100% transmission (i.e. the brightest state), for each normalized T.sub.vis step the desired value can be calculated according to the relation 1000*voltage/24 V. The resulting look-up table (LUT) is shown in Table 2.

TABLE-US-00002 TABLE 2 T.sub.vis LUT for W-A LUT for W-B  0% 54 83 10% 67 92 20% 75 104 30% 83 117 40% 92 129 50% 104 146 60% 121 171 70% 146 204 80% 196 275 90% 300 417 100%  708 1000

[0114] For the same windows W-A and W-B the voltage-transmission behaviour as shown in Table 3 and the look-up table as shown in Table 4 are obtained accordingly at 80° C.

TABLE-US-00003 TABLE 3 T.sub.vis Voltage (V) for W-A Voltage (V) for W-B  0% 1.3 2.0 10% 1.6 2.2 20% 1.8 2.5 30% 1.9 2.7 40% 2.1 2.9 50% 2.3 3.2 60% 2.7 3.8 70% 3.2 4.5 80% 4.1 5.7 90% 6.1 8.6 100%  17.5 24.0

TABLE-US-00004 TABLE 4 T.sub.vis LUT for W-A LUT for W-B  0% 54 83 10% 67 92 20% 75 104 30% 79 113 40% 88 121 50% 96 133 60% 113 158 70% 133 188 80% 171 238 90% 254 358 100%  729 1000

REFERENCE NUMERALS

[0115] 10 communication module [0116] 12 first communication bus [0117] 20 controller [0118] 22 second communication bus [0119] 24 analogue input device [0120] 30 switchable window [0121] 32 electrical connection [0122] 100 building management system [0123] 110 control unit