Patent Publication Number: US-2016241157-A1

Title: Small power harvesting methods for powering control devices using a single power line

Description:
The disclosed exemplary embodiments relate generally to electrical equipment, and more particularly to providing power to control devices. 
     BACKGROUND 
     In many existing AC wiring systems, the neutral line may not be accessible because it may be routed separately from the phase line and may be connected directly to the load. In systems using traditional switches or other passive devices, access to the neutral line may not be required.  FIG. 1  schematically illustrates such a system where power is provided to a load  105  from an AC line voltage source  100  by a neutral wire  110  that is not accessible, and by a phase wire  115  with a conventional switch  120  in series with the load  105 . In this example, at least the neural wire  110  is not accessible. In other examples, the AC line voltage source  100  and the load  105  may also be inaccessible. However, many active controllers, for example, programmable controllers for HVAC and lighting, require connections to both the phase and neutral lines for their own operating power. It may be impossible to Install an active controller requiring both phase and neutral connections into a circuit with an inaccessible neutral line. 
     It would be desirable to provide an apparatus and method for providing power in the absence of an accessible neutral conductor. 
     SUMMARY 
     As described herein, the exemplary embodiments overcome one or more of the above or other disadvantages known in the art. 
     The exemplary embodiments are directed to a power harvesting circuit including a first switch connected in series between an AC source and a load, a switch control circuit connected to the switch and operable to cause the switch to cycle AC power to the load, and a power collection circuit for collecting power resulting from cycling the AC power for use by a load control circuit. 
     The switch control circuit may be operable to cause the first switch to cycle AC power to the load by periodically applying power to the load. 
     The power collection circuit may include a transformer primary winding in series with the AC source and the load, and a rectifier connected to a secondary winding of the transformer to provide power to the load control circuit. 
     The switch control circuit may be operable to cause the first switch to cycle AC power to the load by periodically interrupting AC power to the load. 
     The power collection circuit may be connected in series with the AC source and the load when the first switch interrupts AC power to the load. 
     The power collection circuit may include a rectifier, an inductor and a capacitor connected in series with the AC source and the load when the first switch interrupts AC power to the load. 
     A DC voltage may be developed across the capacitor when the first switch interrupts AC power to the load and is used to provide power to the load control circuit. 
     The power harvesting circuit may include a comparator with inputs connected to the capacitor and a voltage reference and an output connected to a second switch configured to disconnect the rectifier, inductor and capacitor when the DC voltage across the capacitor exceeds a threshold determined from the voltage reference. 
     The exemplary embodiments are also directed to a method of power harvesting including cycling AC power to a load using a switch, and collecting power generated by cycling the AC power and providing the collected power for use by a load control circuit. 
     The method may include cycling AC power to the load by periodically applying AC power to the load. 
     Collecting power generated by cycling the AC power may include rectifying power from a transformer connected in series with the AC source and the load to provide power to the load control circuit. 
     The method may include cycling AC power to the load by periodically interrupting power to the load. 
     Collecting power generated by cycling the AC power may be performed when power to the load is interrupted. 
     Collecting power generated by cycling the AC power may include charging a capacitor through a rectifier and an inductor in series with the AC source and the load when power to the load is interrupted. 
     Providing the collected power for use by the load control circuit may include providing a DC voltage developed across the capacitor when power is interrupted to the load to the load control circuit. 
     The method may include comparing the DC voltage developed across the capacitor with a voltage reference and disconnecting the rectifier, inductor and capacitor when the voltage across the capacitor exceeds a threshold determined from the voltage reference. 
     The exemplary embodiments are also directed to an active controller having a load control circuit, and a power harvesting circuit including first switch connected in series between an AC source and a load, a switch control circuit connected to the switch and operable to cause the switch to cycle AC power to the load, and a power collection circuit for collecting power resulting from cycling the AC power for use by a load control circuit. 
     The switch control circuit may be operable to cause the first switch to cycle AC power to the load by periodically applying power to the load. 
     The power collection circuit may include a transformer primary winding in series with the AC source and the load, and a rectifier connected to a secondary winding of the transformer to provide power to the load control circuit. 
     The switch control circuit may be operable to cause the first switch to cycle AC power to the load by periodically interrupting AC power to the load. 
     The power collection circuit may be connected in series with the AC source and the load when the first switch interrupts AC power to the load. 
     The power collection circuit may include a rectifier, an inductor and a capacitor connected in series with the AC source and the load when the first switch interrupts AC power to the load. 
     A DC voltage may be developed across the capacitor when the first switch interrupts AC power to the load and is used to provide power to the load control circuit. 
     The active controller may include a comparator with inputs connected to the capacitor and a voltage reference and an output connected to a second switch configured to disconnect the rectifier, inductor and capacitor when the voltage across the capacitor exceeds a threshold determined from the voltage reference. 
     These and other aspects and advantages of the exemplary embodiments will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. Moreover, the drawings are not necessarily drawn to scale and unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. In addition, any suitable size, shape or type of elements or materials could be used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  schematically illustrates an AC system where power is provided to a load; 
         FIG. 2  shows a block diagram of a power harvesting application according to the disclosed embodiments; 
         FIG. 3  shows a block diagram of a load control circuit for use with the disclosed embodiments; 
         FIG. 4  shows a block diagram of an exemplary circuit implementation of the power harvesting application illustrated in  FIG. 2 ; 
         FIG. 5  shows a block diagram of another exemplary circuit implementation of the power harvesting application illustrated in  FIG. 2 ; 
         FIG. 6  shows simulation results of the exemplary embodiment of  FIG. 5 . 
         FIG. 7  shows a set of simulated results for the embodiment of  FIG. 5  where the harvested current causes pulses across a load; and 
         FIG. 8  shows a simulated result of optionally providing a capacitor in parallel with the load for applications where the load draws a reduced current. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed embodiments are directed to a method and apparatus for providing power in the absence of an accessible neutral wire or conductor. The exemplary embodiments generally operate to cycle power to a load, and collect power resulting from cycling the power. As used herein, the term “cycling power” may be defined as periodically applying power to the load or periodically interrupting power to the load. 
       FIG. 2  shows a block diagram of an example of the disclosed embodiments. A power harvesting circuit  125  is connected in series between the AC line voltage source  100  and the load  105 . The power harvesting circuit  125  generally includes circuitry  130  for collecting and delivering power to load control circuit  135  which operates to control AC power delivered to the load  105 . Load control circuit  135  may include one or more of a programmable multifunction controller, programmable on-off timer, dimming controller, wireless controller, occupancy sensor, light triggered device, or any module or circuitry for controlling power to a load. While the power harvesting circuit  125  and the load control circuit  135  may be separate, it should be understood that the power harvesting circuit  125  and the load control circuit  135  of the disclosed embodiments may be implemented together or integrated together as at least part of an active controller  140 . 
     As shown in  FIG. 3 , the load control circuit  135  generally includes computer readable program code  305  stored on at least one computer readable medium for operating the power harvesting circuit  125  and for controlling AC power delivered to the load  105 . The computer readable medium may be a memory  310  of the microcontroller  115 . The load control circuit  135  may also include a processor  315  for executing the computer readable program code  305 . In at least one aspect, the load control circuit  135  may include one or more input or output devices, including a user interface  320 . The user interface  320  may include user controls  325  for programming the load control circuit  135  and for receiving user input and for providing information to the user. In at least one embodiment, the user controls  325  may be used instead of the conventional switch  120 . The load control circuit  135  may also include driver circuitry  330  for driving components of the power harvesting circuit  125 . The load control circuit  135  may also include power conditioning circuitry  335  for conditioning and optionally storing power provided by the power harvesting circuit  125 . The power conditioning circuitry  335  may include a power storage device, for example, one or more of a battery or a capacitor. 
       FIG. 4  shows an exemplary embodiment of a power harvesting circuit  425  according to the disclosed embodiments, where power may be harvested or collected when power is provided to the load  105 . In this embodiment, the power harvesting circuit  425  may include a power collection circuit  440 , a switch  430 , and a switch control circuit  435 ,  445 . The power collection circuit  440  may include a transformer  410 , a rectifier  415 , and an optional filter  420 . A primary winding  410 A of the transformer  410  may be connected in series between the AC line voltage source  100  and the switch  430 , and the switch  430  may be connected in series between the primary winding  410 A of the transformer  410  and the load  105 . A secondary winding  410 B of the transformer  410  may be connected to an AC input of the rectifier  415 . The DC output of the rectifier  415  may be connected to the load control circuit  135 , optionally though the filter  420 . The load control circuit  135  may include a switch control circuit  445  connected to the switch  430  for controlling the operation of the switch  430 . Some embodiments may include a switch control circuit  435  separate from the load control circuit  135 . 
     When the switch  430  is closed, current flows through the transformer  410 , is rectified by the rectifier  415 , may optionally be filtered or otherwise conditioned by filter  420  and provided to the load control circuit  135 . The switch  430  may be an electronically controlled switch and may be controlled by the switch control circuit  435 ,  445 . When power is applied to the load, the power harvesting circuit  425  provides power to the load control circuit  135 . The power conditioning circuitry  335  of the load control circuit  135  may optionally store the power for use by the load control circuit  135  when the switch  430  is open. 
     In one or more embodiments, when power is not normally applied to the load  105  and the switch  430  is normally open, the switch control circuit  435 ,  445  may operate to close the switch  430  periodically to generate power for the load control circuit  135 . The switch control circuit  435 ,  445  may apply a signal with a constant duty cycle and period to the switch  430 . In some embodiments the switch control circuit  435 ,  445  may only apply the signal when the load control circuit  135  determines that power is required. In one or more embodiments, the switch control circuit  435 ,  445  may also apply a signal to the switch  430  with a variable duty cycle and a variable period. The duty cycle and period of the switch closure may be selected to be less than a reaction time of the load  105 . Thus, the switch  430  may be in the on or conducting state for a short period of time such that there is no perceptible activity by the load. For example, where the load  105  is an incandescent lamp, the duty cycle and period of the switch closure may be selected to provide power to the load control circuit  135  without lighting the lamp. 
       FIG. 5  shows another embodiment of a power harvesting circuit  525 , according to the disclosed embodiments, where power is harvested or collected when power is interrupted to the load  105 . In this embodiment, the power harvesting circuit  525  may include a power collection circuit  505  and a switch control circuit  510 . The power collection circuit  505  may include a switch  515  in series between the AC line voltage source  100  and the load  105 . In parallel with the switch  515 , another switch  520 , a diode  530 , an inductor  535  and a capacitor  540  may be connected in series. A free wheeling diode  545  may be connected in parallel with the series connected inductor  535  and capacitor  540  to eliminate any voltage spikes across the inductor  535 . The terminals  565 ,  570  of the capacitor  540  may be connected to the load control circuit  135  to supply power to the load control circuit  135 . 
     The switch control circuit  510  may include a comparator section  550  and a signal generator section  555 . The comparator section  550  compares the voltage Vcc across capacitor  540  with a voltage reference  560  and generates a Vcc_HIGH signal for controlling switch  520  when the voltage Vcc across capacitor  540  exceeds a predetermined threshold. The signal generator section  555  combines the Vcc_HIGH signal and a COMMAND signal to provide a GATING signal for controlling switch  515 . 
     The COMMAND signal may be provided by the load control circuit  135  or a separate switch command circuit  580 . The load control circuit  135  or the switch command circuit  580  may provide the COMMAND signal with a constant duty cycle and period. In some embodiments the load control circuit  135  or the switch command circuit  580  may only provide the COMMAND signal when the load control circuit  135  determines that power is required. In one or more embodiments, the load control circuit  135  or the switch command circuit  580  may also provide the COMMAND signal with a variable duty cycle and a variable period. The duty cycle and period of the COMMAND signal may be selected such that the resulting GATING signal causes the switch  515  to be open for a time period less than a reaction time of the load  105 . Thus, the switch  515  may be in the off or non-conducting state for a short period of time such that there is no perceptible change in activity by the load. For example, where the load  105  is an incandescent lamp, the duty cycle and period of the COMMAND signal may be selected to interrupt power to the lamp without perceptively extinguishing or otherwise changing the output of the lamp. 
     In operation, switch  520  is normally closed and switch  515  is closed to apply power to the load  105 . The GATING signal is provided to open the switch  515  periodically to generate power for the load control circuit  135 . When switch  515  opens, power is provided through switch  520 , rectified by diode  530 , and applied to a first terminal  565  of capacitor  540  through inductor  535 . A second terminal  570  of capacitor  540  is grounded through the load  105 . The power accumulated across terminals  565 ,  570  terminals of the capacitor  540  is provided to the load control circuit  135 . If the voltage Vcc across capacitor  540  exceeds a predetermined threshold, the comparator section  550  generates the Vcc_HIGH signal causing switch  520  to open, preventing capacitor  540  from charging until the voltage Vcc no longer exceeds the predetermined threshold. 
       FIG. 6  shows a set of exemplary simulated results for the embodiment of  FIG. 5  where the AC line voltage is 240 VAC, the load  105  draws  1 A, and the generated COMMAND signal is a 10 Hz square wave. By interrupting the power to the load every 0.05 seconds the power collection circuit  505  produces a Vcc of approximately 5 VDC when the current drawn by the load control circuit  135  is approximately 5 mA. 
     Generally, the amount of power harvested for use by the load control circuit  135  may be insignificant when compared to the current drawn by the load  105 . However, in applications where the effective resistance of the load is higher and the current drawn by the load is smaller, the amount of power available for harvesting may be decreased because the load is in series with the power harvesting circuitry. Furthermore, it may be difficult to select a duty cycle and period for the signals from the load control circuit  135  or the switch control circuit  435 ,  580  that is less than the reaction time of the load  105 . 
       FIG. 7  shows a set of simulated results for the embodiment of  FIG. 5  where the current drawn by the load  105  may be approximately 1/20 of the current drawn by the load in the simulation depicted in  FIG. 6 . Pulses  710  may appear across the load  105  when power has been interrupted and may create disturbances or may cause a reaction by the load, for example, lighting or extinguishing a light when the load is an incandescent lamp.  FIG. 8  shows the simulated result  810  of optionally providing a capacitor  575  ( FIG. 5 ) in parallel with the load  105  to compensate for the decreased load current. 
     The disclosed embodiments provide techniques for providing power for control circuits in the absence of an accessible neutral conductor. The embodiments include circuitry for cycling power to a load and harvesting or collecting power available as a result of cycling the power. The power harvesting circuits disclosed herein may be implemented to provide power to a pre-existing control circuit, or the power harvesting circuits and a control circuit may be implemented together as at least part of an active controller. 
     Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, all such and similar modifications of the teachings of the disclosed embodiments will still fall within the scope of the disclosed embodiments. 
     Furthermore, some of the features of the exemplary embodiments could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the disclosed embodiments and not in limitation thereof.