WO2016118175A1

WO2016118175A1 - Method and apparatus for efficient lighting element operation

Info

Publication number: WO2016118175A1
Application number: PCT/US2015/019433
Authority: WO
Inventors: Matthew LIOTTA; John DE ROO
Original assignee: Podponics, Inc.
Priority date: 2015-01-23
Filing date: 2015-03-09
Publication date: 2016-07-28

Abstract

In a method of powering a lighting system that includes a plurality of lighting elements (312) electrically coupled in series, current from a multi-phase AC power source (10) is rectified (310) so as to generate a rectified DC power signal (110). An instantaneous voltage of the DC power signal (110) is sensed. A minimum voltage threshold necessary to drive the plurality of lighting elements (312) is determined. One of the lighting elements (316) is decoupled from the plurality of lighting elements (312) when the instantaneous voltage falls below the minimum voltage threshold. The one of the lighting elements (316) is coupled to the plurality of lighting elements so as to be in series therewith when instantaneous voltage is at least the threshold voltage.

Description

METHOD AND APPARATUS FOR EFFICIENT LIGHTING ELEMENT

OPERATION

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of, US Patent Application Serial No.

62/107,293, filed 01/23/2015, the entirety of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention

[0002] The present invention relates to lighting systems and, more specifically, to a system of controlling lighting elements efficiently.

[0003] 2. Description of the Related Art

[0004] Because of their energy efficiency, LED lighting systems are increasingly used in industrial and agricultural applications. For example, LED lighting is frequently used in warehouse and factory lighting. As another example, LEDs are used in many indoor hydroponic agricultural systems for growing vegetables.

[0005] In a hydroponic agricultural system, efficient use of lighting can have a substantial impact on the profit margin for the operation. A leafy produce plant, such as lettuce, can use different amounts of light at different periods of its life cycle. For example, a seedling can absorb much less light than a mature plant. Also, light that falls in the spaces between immature plants is wasted, whereas light directed to those spaces once that plant has grown into them can help the plant to mature faster.

[0006] Most large scale industrial and agricultural facilities receive three phase power from the local power utility. Three phase power tends to be more economical than single phase current at the industrial scale. Such facilities often use three phase loads in some applications, but derive single phase 120V through a transformer from the three phase power source to deliver standard 120V single phase power for applications such a lighting.

[0007] LED lighting elements typically require direct current (DC) at a narrow range of voltages in order to operate. One typical type of industrial LED lighting element requires a DC voltage in an operating range of between 40V to 50V. In such industrial settings, 120 VAC power is derived from three phase 208 VAC power and 277VAC single phase power is derived from 480VAC via a transformer. An LED driver converts this power into direct current power with a voltage that corresponds to the operating range of the LED fixture being employed. Typical transformers exhibit loss of about 5% and LED drivers exhibit a loss of about 8%, which combined results in a loss of around 12% to 13%. In energy intensive business applications such a loss can translate to higher operational expenses.

[0008] Therefore, there is a need for a more efficient system for operating LEDs and other types of lighting elements.

SUMMARY OF THE INVENTION

[0009] The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a lighting circuit configured to generate light in response to current, from a power source, that has an instantaneous voltage. A plurality of lighting elements is electrically coupled in series and is configured to be powered by the power source. Each of the plurality of lighting elements has a minimum operating voltage associated therewith. A minimum voltage threshold is a sum of all of the minimum operating voltages of each lighting element in the plurality of lighting elements. A switch is configured selectively to couple a selected one of the plurality of lighting elements to the plurality of lighting elements when the switch is in a first state and to decouple the selected one of the plurality of lighting elements from the plurality of lighting elements when the switch is in a second state, different from the first state. A voltage sensor is configured to measure the instantaneous voltage. A controller is responsive to the voltage sensor and is configured to drive the switch into the first state when the instantaneous voltage is at least the minimum voltage threshold and is configured to drive the switch into the second state when the instantaneous voltage is less than the minimum voltage threshold. [0010] In another aspect, the invention is a lighting system that is configured to be powered by a multi-phase power source. A rectifying unit is configured to rectify power from the multi-phase power source so as to generate a DC voltage having an instantaneous voltage associated therewith. A plurality of lighting elements is electrically coupled in series and is configured to be powered by the DC voltage. Each of the plurality of lighting elements has a minimum operating voltage associated therewith. A minimum voltage threshold is a sum of all of the minimum operating voltages of each lighting element in the plurality of lighting elements. A switch is configured selectively to couple a selected one of the plurality of lighting elements to the plurality of lighting elements when the switch is in a first state and to decouple the selected one of the plurality of lighting elements from the plurality of lighting elements when the switch is in a second state, different from the first state. A voltage sensor is configured to measure the instantaneous voltage. A controller is responsive to the voltage sensor and is configured to drive the switch into the first state when the instantaneous voltage is at least the minimum voltage threshold and is configured to drive the switch into the second state when the instantaneous voltage is less than the minimum voltage threshold.

[0011] In yet another aspect, the invention is a method of powering a lighting system that includes a plurality of lighting elements electrically coupled in series. Current from a multi-phase AC power source is rectified so as to generate DC power. An instantaneous voltage of the DC power signal is sensed. A minimum voltage threshold necessary to drive the plurality of lighting elements is determined. One of the lighting elements is decoupled from the plurality of lighting elements when the instantaneous voltage falls below the minimum voltage threshold. The one of the lighting elements is coupled to the plurality of lighting elements so as to be in series therewith when instantaneous voltage is at least the threshold voltage.

[0012] These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure. BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

[0013] FIG. 1 is a block diagram of a first embodiment of a lighting system.

[0014] FIG. 2 is a block diagram of a second embodiment of a lighting system.

[0015] FIG. 3A is a schematic diagram of a lighting system with a single switchable lighting element.

[0016] FIG. 3B is a schematic diagram of a voltage sensor and switch control circuit.

[0017] FIG. 4 is a schematic diagram of a switchable lighting matrix.

[0018] FIG. 5 is a diagram of a lighting system employed in an agricultural

application.

DETAILED DESCRIPTION OF THE INVENTION

[0019] A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of "a," "an," and "the" includes plural reference, the meaning of "in" includes "in" and "on."

[0020] As used herein the term "lighting element matrix" includes any type of combination of lighting elements, including a linear series of lighting elements and an array of lighting elements with some of the elements being connected in series, in which some or all of the lighting elements can be switched out of the combination. Certain lighting element matrices allow reconfiguration of the elements, such as reconfiguring an element originally in series with another element to be in parallel with that element. [0021] As shown in FIG. 1, one embodiment of a lighting circuit 100 includes a rectifying unit 110 (such as a diode-based full wave rectifier) that receives power from a multiphase power source 10 (such as a nominally 480VAC three phase power source) and rectifies it to a direct current (DC) supply 112 (such as nominally 648VDC power). The rectifying unit 110 can also include a filter that flattens the output from the rectifying unit 110 by reducing voltage deviations. A switchable lighting element matrix 130 includes a plurality of lighting elements in series. (The lighting elements can include, for example, LEDs and other lighting technologies including, plasma bulbs, light emitting polymers, nano-structure field emitters, piezophotonic devices and other photonic devices.)

[0022] In an LED-based embodiment, the sum of the operating voltage ranges associated with the LEDs is such that the nominal voltage associated with the direct current supply 112 is within the operating voltage range sum. Many public utility power supply voltages can vary over time with periodic voltage drops that will cause the instantaneous DC supply voltage to fall below the lower limit of the series operating range. A voltage sensor and switch control unit 120 senses the instantaneous voltage from the DC supply 112 and if the instantaneous voltage drops below the lower limit of the series operating range, then the sensor and switch control unit 120 will reconfigure the lights in the switchable LED matrix 130 so that the sum of the lower limits of the operating ranges is below the instantaneous voltage.

[0023] For example, if the DC supply 112 has a nominal 648 VDC voltage associated therewith and if the LEDs have an average operating voltage range of 40V to 50V, then the switchable LED matrix 130 could include 14 LEDs in series. The operating range of the series of LEDs would then be 560V to 700V. If the voltage sensor and switch control 120 senses that the DC supply 112 drops below 560V to, for example, to 530V, then it will cause the switchable LED matrix to remove one of the LEDs from the series so that there are 13 LEDs in series instead of 14. Since the operating range of 13 LEDs would be 520V to 650V, a 530V supply would be sufficient to drive the reconfigured series of LEDs. If the instantaneous voltage were to drop further, for example to 490V, the voltage sensor and switch control 120 could (in some embodiments) remove another LED from the series, thereby lowering the operating range to 480V to 600V. The LEDs taken out of series could simply be bypassed or they could be put in parallel with other LEDs in the series, depending on the lighting requirements of the system. [0024] In one embodiment, a rectifier may not be needed when power from certain variable voltage power sources 20 is employed. Such power sources could include DC power sources, power taken from a single phase AC power source or AC power taken between two rails of a three phase power source.

[0025] One simple embodiment is shown in FIGS. 3A and 3B. In this embodiment power from a rectifier 310 is delivered to a plurality of LEDs 312 electrically coupled in series. One of the LEDs 316 is coupled to a switch 314 that can couple LED 316 to the other LEDs 312 in series therewith while in a first state and that can bypass LED 316 by outputting directly to ground via a bypass line 318 when in a second state. In this embodiment, if the LEDs are rated at 40V-50V, they will become inoperable if the instantaneous voltage from the rectifier 310 drops below 560V and, in such a case, the voltage sensor and switch control unit 320 will decouple LED 316 from the series until the instantaneous voltage returns to a level above 560V. In this simple embodiment, the voltage sensor and switch control 320 could be an op-amp configured as a comparator and the switch 316 could simply be a transistor, such as a power field effect transistor, as shown in FIG. 3B.

[0026] A more complex embodiment is shown in FIG. 4, in which each one of LEDs 412a-e in the series is coupled to a switch 414 that can bypass 418 each LED. In this embodiment, the voltage sensor and switch control unit 420 can be a programmable device (such as a field programmable gate array; a processor; a programmable logic array; a micro-controller; or a programmable logic device) that can be programmed to switch individual LEDs on an off based on predefined or dynamically determined criteria. In one application, each time that the voltage sensor and switch control unit 420 needs to switch off an LED, it can switch a different one of the LEDs off so as to lengthen the average lifetime of all of the LEDs 412a-e. (For example, the first time LED 412a is switched off, the second time LED 412b is switched off, etc.) In other applications, certain LEDs are favored for staying on, such as the LEDs in the center (e.g., LEDs. 412b, 412c, and 412d could always be on and LEDs 412a and 412e could be switched off when needed).

[0027] In an agricultural embodiment, as shown in FIG. 5, a plurality of plants 502 are raised in confinement in an interior location. Standard three phase power 30 is supplied, for example, offsite by a utility company. The three phase power is rectified by a full wave rectifier 510 to generate DC power 512. A lighting unit 540 includes a plurality of LEDs and provides growth light to the plants 502. Each of the LEDs (or at least selected ones of the LEDs) is controlled by a switching unit 530, which could include a switching matrix. The switching unit 530 is controlled by a switch control unit 522 (which could be a programmable device coupled to the switching unit 530 by a control bus 524) that receives control input from an instantaneous voltage sensor 520, which senses the instantaneous voltage of the DC power 512. The programmable switch control unit 522 can switch selected ones of the LEDs 544 off during low power transients, while leaving other ones of the LEDs 542 on. The programmable switch control unit 522 can also switch selected ones of the LEDs on or off at different stages of the plant growth to ensure optimal light exposure for the plants 502.

[0028] In one embodiment the lighting unit could employ lighting elements that generate light of different wavelengths and the switch control unit could select lighting elements based on a desired wavelength mix for the particular application. Other lighting criteria can be used in programming the switch control unit. For example, the system can be programmed to handle failed LEDs gracefully. If N LEDs are required to handle the maximum expected Voltage, but N+M LEDs are in the matrix and all of them are switchable, then the system can withstand M LED failures without loss of functionality at high voltages. The light uniformity will suffer, particularly if multiple adjacent LEDs fail, but the system will be able to continue to function.

[0029] The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.

Claims

CLAIMS What is claimed is:

1. A lighting circuit configured to generate light in response to a power source, that has an instantaneous voltage, comprising:

(a) a plurality of lighting elements electrically coupled in series and configured to be powered by the power source, each of the plurality of lighting elements having a minimum operating voltage associated therewith, a minimum voltage threshold being a sum of the minimum operating voltage of all of the lighting elements in the plurality of lighting elements;

(b) a switch that is configured selectively to couple a selected one of the

plurality of lighting elements to the plurality of lighting elements when the switch is in a first state and to decouple the selected one of the plurality of lighting elements from the plurality of lighting elements when the switch is in a second state, different from the first state;

(c) a voltage sensor configured to measure the instantaneous voltage; and

(d) a controller that is responsive to the voltage sensor and that is configured to drive the switch into the first state when the instantaneous voltage is at least the minimum voltage threshold and configured to drive the switch into the second state when the instantaneous voltage is less than the minimum voltage threshold.

2. The lighting circuit of Claim 1, wherein the lighting elements comprise LEDs.

3. The lighting circuit of Claim 1, wherein the power source comprises a rectifying unit that comprises

(a) a voltage rectifier; and

(b) a filter that is configured to reduce voltage deviations in output from the voltage rectifier.

4. The lighting circuit of Claim 1, wherein the controller comprises a programmable device.

5. The lighting circuit of Claim 4, wherein the programmable device comprises a device selected from a list consisting of: a field programmable gate array; a processor; a programmable logic array; a micro-controller; a programmable logic device; an ASIC; and combinations thereof.

6. The lighting circuit of Claim 1, wherein the switch is a member of a plurality of switches, each of the plurality of switches configured to selectively couple and decouple a corresponding one of the plurality of lighting elements based on predefined criteria.

7. The lighting circuit of Claim 6, wherein the controller is further configured to select different ones of the plurality of lighting elements for decoupling in different instances of when the instantaneous voltage goes below the threshold voltage.

8. The lighting circuit of Claim 6, wherein the controller is further configured to select ones of the plurality of lighting elements for decoupling based on operational requirements of the lighting system.

9. A lighting system, configured to be powered by a multi -phase power source,

comprising:

(a) a rectifying unit configured to rectify power from the multi-phase power source so as to generate a DC voltage having an instantaneous voltage associated therewith;

(b) a plurality of lighting elements electrically coupled in series and configured to be powered by the DC voltage, each of the plurality of lighting elements having a minimum operating voltage associated therewith, a minimum voltage threshold being a sum of all of the minimum operating voltage of each lighting element in the plurality of lighting elements;

(c) a switch that is configured selectively to couple a selected one of the

(d) a voltage sensor configured to measure the instantaneous voltage; and (e) a controller that is responsive to the voltage sensor and that is configured to drive the switch into the first state when the instantaneous voltage is at least the minimum voltage threshold and configured to drive the switch into the second state when the instantaneous voltage is less than the minimum voltage threshold.

10. The lighting system of Claim 9, wherein the lighting elements comprise LEDs.

The lighting system of Claim 9, wherein the rectifying unit comprises:

(a) a voltage rectifier; and

(b) a filter that is configured to reduce voltage deviations in output from

voltage rectifier.

12. The lighting system of Claim 1 1, wherein the multi-phase power source comprises a three phase AC power source and wherein the voltage rectifier comprises a three phase power rectifier.

13. The lighting system of Claim 9, wherein the controller comprises a programmable device.

14. The lighting system of Claim 13, wherein the programmable device comprises a device selected from a list consisting of: a field programmable gate array; a processor; a programmable logic array; a micro-controller; a programmable logic device; an ASIC; and combinations thereof.

15. The lighting system of Claim 9, wherein the switch is a member of a plurality of switches, each of the plurality of switches configured to selectively couple and decouple a corresponding one of the plurality of lighting elements based on predefined criteria.

16. The lighting system of Claim 15, wherein the controller is further configured to select different ones of the plurality of lighting elements for decoupling in different instances of when the instantaneous voltage goes below the threshold voltage.

17. The lighting system of Claim 15, wherein the controller is further configured to select ones of the plurality of lighting elements for decoupling based on operational requirements of the lighting system.

18. A method of powering a lighting system that includes a plurality of lighting

elements electrically coupled in series, comprising the steps of:

(a) rectifying current from a multi-phase AC power source so as to generate a rectified DC power signal;

(b) sensing an instantaneous voltage of the DC power signal;

(c) determining a minimum voltage threshold necessary to drive the plurality of lighting elements; and

(d) decoupling one of the lighting elements from the plurality of lighting

elements when the instantaneous voltage falls below the minimum voltage threshold and coupling the one of the lighting elements to the plurality of lighting elements so as to be in series therewith when instantaneous voltage is at least the threshold voltage.

19. The method of Claim 18, wherein the lighting elements comprise LEDs.

20. The method of Claim 18, further comprising the step of decoupling different ones of the lighting elements during successive instances of the instantaneous voltage falling below the minimum threshold voltage.

21. The method of Claim 18, further comprising the step of selecting which one of the lighting elements to decouple based on predefined criteria.

22. The method of Claim 18, further comprising the step of filtering the rectified DC power signal so as to reduce voltage deviations therein.