Patent Publication Number: US-11641099-B2

Title: Arc detection system

Description:
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/955,240, filed on Dec. 30, 2019. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to arc detection systems, and more particularly, arc detection systems for LED lighting systems. 
     Description of the Related Art 
     Perimeter or border lights (“perimeter lighting”) are commonly used on buildings to accentuate the structure, to draw customer attention to the building, and to provide safety lighting. Most conventional perimeter lights use neon bulbs for the light source. Some of the disadvantages of neon lighting is that neon bulbs have a relatively short life, are fragile and can consume a relatively large amount of power. Also, neon bulbs can experience difficulty with cold starting, which can lead to the bulb&#39;s failure. 
     Light emitting diodes (LED or LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. Typically, wire bonds are used to apply a bias across the doped layers, injecting holes and electrons into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED. A typical high efficiency LED comprises an LED chip mounted to an LED package and encapsulated by a transparent medium. The efficient extraction of light from LEDs and the quality of that light are major concerns in LED package fabrication. 
     Developments and improvements in LED technology have resulted in devices that are brighter, more efficient and more reliable. LEDs are now being used in many different applications that were previously the realm of neon or incandescent bulbs; some of these include commercial and residential lighting, architectural displays, automobile taillights and traffic signals. As the efficiency of LEDs improve it is expected that they will be used in most lighting applications. 
     Perimeter lighting systems have been developed so that they rely primarily on LEDs as their light source. Examples of these are described in U.S. Pat. Nos. 6,776,504, &amp;,234,838 and 8,511,849, all of which are assigned to the assignee of this application, and are incorporate by reference in their entirety. Some of the embodiments described in these patents can have an elongated LED array printed circuit board (PCB) that hold LEDs that are the light source for the perimeter lighting. The LED array PCB can have conductive traces for conducting the primary power (e.g. 24 volts) and the return power for the LEDs. 
     A relatively rare occurrence with this arrangement is that arcing can occur between the power and return traces on the PCB. Multiple arching incidents can cause the temperature of the PCB to exceed 200 degrees Celsius at particular locations, and this can cause localized burning of the PCB. This localized burning can create a carbon powder, and once enough carbon builds up, and subsequent arc can generate a fire on the PCB at the carbon powder. This rare occurrence can result in the fire damage to the PCB, perimeter lighting fixture, and the surrounding area. 
     SUMMARY OF THE INVENTION 
     The present invention generally directed to a system that prevents fire damage to solid state (LED) based light sources by providing an arc detection system that can be used to detect acing in LED based light fixtures. Once the arcing is detected, power can be quickly turned off to the lighting system. As mentioned above, arcing can cause the build-up of carbon at on the PCB where the LEDs are mounted. This removal of power to the LEDs upon arcing can prevent subsequent arcing, can prevent the build-up of carbon on the PCB and can prevent a fire from starting in the carbon powder already built-up on the PCB. 
     One embodiment of an arc detection circuit according to the present invention comprises a high pass filter circuit arranged to accept an electrical signal with an arc current component having one or more arcing events and a direct current (DC) component, wherein the high pass filter passes only the arc current component. An arc detection circuit is included that accepts the arc current component and filters out arcing events below a threshold. Wherein the arc detection circuit provides an arcing signal with arcing events above said threshold. A microcontroller is also included that accepts the arcing signal to generate control signals based on the arcing signal. In some embodiment, the control signals can be used to control a power supply. 
     The systems according to the present invention can comprise many different features as described below. These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings which illustrate by way of example the features of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a waveform showing operation of one embodiment of an arc detection system according to the present invention; 
         FIG.  2    is a circuit schematic of another embodiment of an arc detection system according to the present invention; 
         FIG.  3    is an arc current application circuit from the schematic shown in  FIG.  2   ; 
         FIG.  4    is a waveform taken from two different points as shown in the circuit of  FIG.  2   ; 
         FIG.  5    is a high pass filter circuit from the schematic shown in  FIG.  2   ; 
         FIG.  6    is a waveform taken from two different points as shown in the circuit of  FIG.  5   ; 
         FIG.  7    is an arc detection circuit from the schematic shown in  FIG.  2   ; 
         FIG.  8    is a waveform taken from three different points as shown in the circuit of  FIG.  7   ; 
         FIG.  9    is the bypass initial spike circuit from the schematic shown in  FIG.  2   ; 
         FIG.  10    is a waveform taken from three different points as shown in the circuit of  FIG.  9   ; 
         FIG.  11    is a detection signal to microcontroller circuit from the schematic shown in  FIG.  2   ; 
         FIG.  12    is a waveform taken from one point as shown in the circuit of  FIG.  11   ; 
         FIG.  13    is flow diagram showing operation of one embodiment of an arc detection system according to the present invention; 
         FIG.  14    is a schematic showing one embodiment of an arc detection circuit according to the present invention; and 
         FIG.  15    is a schematic showing one embodiment of a microcontroller circuit that can be used arc detection systems according to the present invention. 
         FIG.  16    is one embodiment of a software process flow diagram according to the present invention for implementing the flow diagram of  FIG.  13   ; 
         FIGS.  17  and  18    show one embodiment of software subroutines that can be used in the flow diagram of  FIG.  16   ; 
         FIG.  19    shows another embodiment of an arc detection circuit according to the present invention; 
         FIG.  20    shows one embodiment of a lighting system utilizing arc detection circuits according to the present invention; 
         FIG.  21    is one embodiment of a software process flow diagram according to the present invention for implementing functions of arc detection circuit according to the present invention; and 
         FIGS.  22  and  23    show one embodiment of software subroutines that can be used in the flow diagram of  FIG.  21   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed embodiments of arc detection systems that can detect arcing in a PCB holding and/or coupled to LEDs arranged in different ways in different systems. The embodiments below are described in relation to LED based displays, but can be used in different systems. This arcing presents the danger of fire within the light fixture housing the LEDs. Carbon powder can build-up on the PCB during arcing events, and if sufficient carbon powder builds up, subsequent arcing can ignite the carbon powder. 
     The embodiments of the present invention can detect that arcing has occurred and can discontinue or disconnect power to the circuit board and the LEDs in response to the arcing event. In some embodiments, the power can be removed after the first arcing event until the light fixture is analyzed and repaired, such as by a technician. In other embodiments, the power can be returned to the PCB after a predetermined time to again monitor for arcing. If arcing again occurs, power can again be removed from the PCB and/or LEDs. This can then be permanently removed until attended to by a technician, or the system can go through additional cycles to determine if arcing continues. After the desired number of cycles, the power will be removed until attended to by a technician. 
     It is understood that the different embodiments according to the present invention can comprise electronic hardware or software, or a combination of the two, to detect arcing and control power to the PCB or LEDs. In some embodiments, the hardware/software can reside fully or partially in the power supply. 
     The present invention is described herein with reference to certain embodiments, but it is understood that the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is further understood that different embodiments can comprise different features, elements and components arranged in different ways. Different embodiments can also be for use in arc detection in many different systems beyond solid state lighting systems. 
     It will be understood that when an element is referred to as being “on” or “connected to” or “coupled to” another element, it can be directly on, in contact or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on”, or “directly connected to” or “directly coupled to” another element, there are no intervening elements present. 
     Although the terms first, second, etc. may be used herein to describe various elements, and/or sections, these elements and/or sections should not be limited by these terms. These terms are only used to distinguish one element, or section from another element, or section. Thus, a first element or section discussed herein could be termed a second element, or section without departing from the teachings of the present invention. 
     One embodiment of a system and method for detecting arcs according to the present invention comprises monitoring the functioning of a power supply driving a display. In some embodiments, the system monitors the output voltage of the power supply to the solid state light source, such as one or more LEDs. This can be accomplished using different hardware or software systems, or systems using a combination of hardware and software. This system can rely at least partially on, and monitor, the over current protection systems of the power supply that based on the characteristics or level of the over current protection, can shut down the power supply. In some embodiments, this shut down can occur if current at the output exceeds a certain threshold. For example, certain power supplies can deliver a current up to 4 amps. If current exceeds this amount, the over protection system of the power supply can shut down the power supply. 
     During an arcing event, the current can increase beyond the threshold of the over current protection, this result in the over current protection circuit to drop. This can be an indication of an arcing condition that can be monitored to shut down the power supply upon repeated arcing events.  FIG.  1    shows waveforms at the power supply showing arcing conditions. 
     One potential drawback to this type of system is that the output voltage may only drop if the arc current is greater than the over current protection threshold. For example, if the power supply has a 4 amp over current protection current, the detection system or circuit may ignore an arc current of less than a 4 amp current. In some systems, the arc fire condition can occur at smaller currents than 4 amps. 
     Another system and method for detecting arcs according to the present invention comprises monitoring the supply current to the LED, with some embodiments constantly monitoring the supply current. If there is a significant enough difference between the previous and current supply current, this can be an indication of an arcing event and the power supply can be shut down. 
     Like above, this approach can be accomplished by using different hardware or software systems, or systems using a combination of hardware and software. This system/method may be an improvement over this system/method described above in that is can detect lower current arc events because it detects the current, not the voltage. One potential drawback of this approach is that the sampling rate may cause inaccuracy in detection. 
     Still another system and method for arc detection according to the present invention utilizes a primarily hardware circuit approach for monitoring the supply current as in the system/method described above. In this embodiment, however, the hardware circuit isolates the arc current from the supply current. Typically, the arc current is located on top of the supply current. The DC supply current is needed for normal operation, so this embodiment isolates the arc current from the DC supply current to detect an arcing event. 
       FIGS.  2 - 12    show one embodiment of an arc detection circuit according to the present invention, and sub-circuits, along with the different electrical signal waveforms at points in the circuit or sub-circuits.  FIG.  2    shows one embodiment of a hardware arc detection circuit  10  according to the present invention. The sub-circuits in this embodiment can comprise an Arc Current Amplifier sub-circuit  12 , a High Pass Filter sub-circuit  14 , and Arc Detection sub-circuit  16 , and a Bypass Initial Spike sub-circuit  18  and Detection Signal to Microcontroller sub-circuit  20 . The sub-circuits are described in more detail below and it is understood that these sub-circuits can include different elements arranged in many different ways, and the detection circuit  10  can comprise different sub-circuits. 
       FIG.  3    shows the Arc Current Amplification sub-circuit  12  from the arc detection circuit  10  shown in  FIG.  2   . In some instances where the circuit  10  is monitoring for arcing condition, the arc current may be too small to be efficiently detected in the detection circuit  10 . The arc current is amplified in the sub-circuit  12 , and the sub-circuit  12  can use many different components arranged in many different ways to amplify the arc current. In the embodiment shown, the arc current is converted to voltage at resister  22  (R 4 ) and then amplified by operational amplifier  24  (L 324 ) to a level that can be utilized by the circuit  10 . 
       FIG.  4    shows the waveforms  26  taken at different points in the sub-circuit  12  and includes a first waveform  28  taken at a first location  30  and a second waveform  32  taken at location  34 . The first waveform  26  comprises the monitored arc current and DC current signal, and second  32  waveform  12  shows the corresponding amplified voltage at the output of the operation amplifier  24 . 
       FIG.  5    shows the High Pass Filter sub-circuit  14  from circuit  10 . During normal operation, the sub-circuit  14  receives the amplified signal from sub-circuit  12  that contains both the arc spike (if any) and normal DC current components. In the embodiment shown, these two components are separated so that the arc detection circuit  10  can address only the spike current of the arc event. The sub-circuit  14  can comprise a capacitor  36  (C 3 } that allows only the spikes in current signal to pass, and blocks the DC component. 
       FIG.  6    shows waveforms  38  at different points in the sub-circuit  14 . The first waveform  40  is taken at a first point  42  prior to capacitor  36  and second waveform  44  is taken at the second point  46  after the signal passes through the capacitor  36 . The first waveform  40  shows the DC and spike components before capacitor  36 , and the second waveform  44  shows the waveform after at point  46  capacitor  36  with no DC current. The second waveform comprises only arc current. It is noted that both the first and second waveforms  40  and  44  include initial turn on spike currents. As discussed below, the arc detection circuits can be arranged so that this turn on spike are not considered to be arcing events by the arc detection circuit. 
       FIG.  7    shows one embodiment of an Arc Detection sub circuit  16  used in the circuit  10  according to the present invention, and  FIG.  8    shows the electrical signal waveforms  50  through the circuit  16  at different locations in the sub-circuit  16 . Many different components can be used for the sub-circuit  16 , with the embodiment shown using operational amplifier  52  and first and second resistors  54 ,  56 . 
     The waveforms  50  include first waveform  58  taken and point  60  in sub-circuit  16  which corresponds to the input  6  at amplifier  52  (U 1 B) and second waveform  62  is taken at point  64  at the input  5  at amplifier  52 , which corresponds to the output of the High Pass Filter sub-circuit  14 . The waveform  58  corresponds to the threshold current signal for arc detection in the sub-circuit  16 . Different embodiments can have different threshold currents to indicate an arcing event, and in the embodiment shown the threshold is 1A (0.5V) The sub-circuit  16  and detection circuit  10  only signal an alarm when the current signal exceeds this level. Third Waveform  66 , which is the electrical signal taken at point  68  (between R 10  and Ml). shows two spikes to reflect detection signals where the arc current exceeded 1A (0.5V). 
       FIG.  9    shows one embodiment of Bypass Turn-On Spike Current sub-circuit  18  used in the circuit  10  according to one embodiment of the present invention. and  FIG.  10    shows waveform  70  of the electrical signal at different locations in the sub-circuit  18 . As mentioned above, during turn-on of the lighting system there can be a spike in current. Following the spike, the power supply regulates the output current to the desired level. The Bypass Turn-on Spike Current sub-circuit  10  is arranged so that the turn-on spike is not detected as an arcing event, and is instead ignored by the arc detection circuit. The sub-circuit  18  can comprise many different elements arranged in many different ways, with the embodiment shown comprising primarily amplifier  72  {U 1 C), transistor  74  (Q 1 ) and surrounding resistor networks. 
       FIG.  10    shows first and second waveforms  74 ,  76  as shown in  FIG.  8    above, with the first waveform  74  having the turn-on spike current and arcing events 6 . The second waveform  76  establishes the threshold for arcing events as described above. The third waveform  78  taken at point  80  in sub-circuit  18  shows the power supply voltage  28 , and reflects that it is not instantaneous at turn-on and instead ramps up slowly. Because of this slow ramp-up, the arc detection circuit  10  does not detect the turn-on spike current and instead only detects the arcing events when at full power supply voltage. Fourth waveform  82  shows the detected arcing events as described above in  FIG.  8   . 
       FIG.  11    shows a Detection Signal to Microcontroller sub-circuit  20  according to one embodiment of the present invention. This sub-circuit can comprise many different components coupled together in many different ways, with the embodiment shown comprising primary a transistor  84  and corresponding resistor network. The sub-circuit  20  is arranged to generate an arc detection signal that can then be send sent to the microcontroller to control operation of the power supply. 
       FIG.  12    shows a waveforms  90  showing a first waveform  92  showing the arcing events as described above. Second waveform  94 , taken at point  96  in sub-circuit  20 , is the arc detection signal to be sent to the microcontroller. In the embodiment shown and as shown in waveform  94 , the sub circuit  20  generates a detect signal that is high (e.g. 5V) during normal operation. Once the arcing spike current is detected, the signal drops to a low (e.g. 0V) that is interpreted by the microcontroller to be an arcing event. 
     The microcontroller can take different actions in response to an arcing event. In some embodiments the microcontroller can turn off the power supply in to the first arcing event. In other embodiments the microcontroller can go through a series of steps to turn off the power supply for a short amount of time in response to an arcing event and then to turn the power supply on again to see if another arcing event occurs. This process prevents the power supply from immediately turning off in response to a single isolated arcing event, and instead only turns off is a series of arcs occur that present a danger of fire. 
       FIG.  13    shows one embodiment of a flow diagram showing this series of steps taken by the microcontroller in response to a series of arcing events. In step  100  the power is turned on to the power supply, the LEDs are energized and emit light, and the power supply proceeds in normal operation. In step  101 , the arc detection circuit monitors for a first arcing event. If a first arcing event is not detected, in step  102  the power supply continues in normal operation. If a first arcing event is detected, in step  104  the arc detection circuit signals the microcontroller and the output power is brought to zero. In step  105 , the microcontroller keeps the output voltage at zero for 1 minute. 
     After 1 minute and in step  106 , the microcontroller causes the power supply to return to maximum output voltage. In step  108 , the arc detection circuit monitors for a second arcing event. If there is none, in step  111  the microcontroller causes the power supply to continue in normal operation. If a second arcing event is detected, in step  110  the microcontroller causes the power supply output voltage to again drop to zero. In step  112  the microcontroller again holds the power supply voltage at zero for one minute before returning the power supply voltage to maximum at step  114 . 
     In this embodiment, the microcontroller causes this turn-off and turn-on process to occur for third, fourth and fifth arcing events as shown in steps  116 ,  118  and  120 . In step  122 , when the fifth arcing event is detected the microcontroller causes the power supply to turn off and remain off until attended to by a repair technician or repair personal. In some embodiments, the arc detection system can include a means of alerting the repair technician that the power supply was turned off do to repeated arcing events. This can comprise a hardware alert such as lighting or mechanical indicator, or can comprise a software indicator that can be read by the repair technician. This arcing indicator can be important to directing the technician to the true cause of the power supply shut-down. 
       FIG.  14    shows an arc detection circuit according to the present invention, and  FIG.  15    shows a microcontroller circuit according to the present invention. The arc detection circuit provides a “Detection” signal to the microcontroller when an arcing event is detected. The microcontroller provides the necessary control signals to control the output voltage of the power supply. The microcontroller also has two indicator LEDs, one of which is an Arc LED that indicates an arcing event detected by the arc detection circuit. 
     It is understood that the process of arc detection as provided for in flow diagram of  FIG.  13    can be implemented using many different software routines and subroutines.  FIG.  16    shows one embodiment of the main program process for one embodiment according to the present invention for implementing the steps in the process in  FIG.  13   .  FIGS.  17 - 18    show one embodiment of software flow for sub-routines that can be used in the process flow of FIG.  16 . It is understood that many different routines and sub-routines beyond those shown, and that the routines and sub-routines can implemented using different software languages. 
     As mentioned above, arc detection circuits according to the present invention can be arranged in many different ways, many different elements, and can have different features beyond the embodiments described above.  FIG.  19    shows another embodiment of an arc detection circuit  200  according to the present invention. Like the arc detection circuit  10  described above, the circuit  200  comprises and Arc Current Amplification sub-circuit  202 , a High Pass Filter sub-circuit  204 , and an Arc Detection Circuit  206 , and these sub-circuits function in much the same way as the corresponding sub-circuits in circuit  10 . The circuit  200  differs from circuit  10  in that the functions of the Bypass Initial Spike sub-circuit are performed in the software run by the microcontroller, resulting in cost savings by eliminating certain hardware components. 
     The circuit  200  is arranged to also have other functions and capabilities. As described above with circuit  10 , the Arc Current Amplification sub-circuit  202  has two current components, the arc current and DC operational current. When and arc condition is present, the arcing current component is separated from the DC operational signal component at the High Pass Filter sub-circuit  204 , and the arcing current component is passed on to the Arc Detection sub-circuit  206 . In the circuit  200 , when arcing conditions are not present the DC component can be used by the microprocessor to determine other important operating conditions, such as over current operation. This DC component is read by the microcontroller at DC output  208  and the microcontroller can use the signal on this output to determine if an overcurrent condition has occurred. 
     The circuit  200  also comprises a Short Circuit Detection sub-circuit  210 . When a short circuit condition exists, the output voltage of the power supply drops to zero, and the sub-circuit  210  detects this signal drops and sends a notification signal to the microprocessor. Pursuant to the above, the circuit  202  provides additional detection and notification capabilities compared to circuit  10  described above, and the circuit  2020  can be used on more than one channel. 
       FIG.  20    shows one embodiment of an LED based lighting system  250  utilizing arc detection circuits according to the present invention. The lighting system  250  comprises a power supply  252  and a voltage regulator  254  that drive first and second LED loads/channels  256 ,  258 . First and second arc detection circuits  260 ,  262  are included, with each being coupled to respective one of the LED channels  256 ,  258 . Each arc detection circuit generates short circuit (SC), arc detection (ARC), and DC overcurrent (ADC) signals that are conducted to the microcontroller  264 . The microcontroller  264  and its software (described above) to control the voltage regulator (and power supply) in the event of short circuit, arcing or overcurrent operating conditions. 
     Like the embodiment above, the microprocessor software to coordinate and accomplish the functions of the circuit  200  can be arranged in many different ways.  FIG.  21    shows the main program process flow for one embodiment of the software according to the present invention.  FIGS.  22  and  23    show different embodiment of software sub-routines that can be used in the program shown in  FIG.  21   . 
     It is understood that many different mechanisms and arrangements can be used in the different systems according to the present invention. Although the present invention has been described in detail with reference to certain configurations thereof, other versions are possible. Therefore, the spirit and scope of the invention should not be limited to the versions described above.