Patent Publication Number: US-9420670-B1

Title: Controller and receiver for a power line communication system

Description:
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application No. 62/074,731, filed Nov. 4, 2014, and which is hereby incorporated by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to dimming control for lighting devices. More particularly, the present invention relates to a power line communication system for transmitting a dimming level to an electronic ballast or LED driver that regulates output current to an associated lighting device. 
     Power line communication systems are known in the art for communicating a dimming level to a lighting circuit such as an electronic ballast or LED driver over an AC power line. The dimming level determines the power output of the lighting circuit and therefore the lighting intensity of an associated lighting device such as a fluorescent lamp or LED array. A power line controller is operable to generate a dimming control signal and to insert that signal on the AC power signal being transmitted over the AC power line to a power line receiver associated with the lighting circuit. The power line receiver then extracts this information from the AC power signal and generates a dimming level signal corresponding to the desired dimming level, which then causes the lighting circuit to generate an output signal to the lighting device in accordance with the desired dimming level. In this manner, a user can control the power consumed by the lighting device and accordingly a lighting intensity. 
     Several prior art solutions exist for transmitting information to a lighting circuit such as an electronic ballast over AC power lines, including using power line modems, high frequency injection codes and line voltage modulation codes. Unfortunately, the equipment required to insert information into the AC power signal and then extract the information at the lighting circuit is expensive. Furthermore, these systems are particularly sensitive to noise and require control signals with high signal levels to communicate the desired dimming level over the power line. This is particularly true if the system is communicating with several lighting circuits at once. 
     What is needed, then, is a power line communication system that inserts information on the AC power signal that is more cost efficient and less sensitive to noise. 
     BRIEF SUMMARY OF THE INVENTION 
     A power line communication system as disclosed herein communicates a desired dimming level to a lighting circuit such as an electronic ballast or an LED driver over an AC power line. The system has a power line controller and a power line receiver connected to the AC power line. The power line controller is configured to generate a control signal and to insert that signal on the AC power signal being transmitted over the AC power line. The power line receiver receives the AC power signal and extracts the control signal from the AC power signal to generate the dimming level signal corresponding with the desired dimming level. The power line receiver may be integral to the lighting circuit or may be a separate apparatus that communicates with the lighting circuit. 
     An embodiment of a power line controller as disclosed herein has a signal pattern circuit for producing a control signal corresponding to a predetermined communication code for communicating dimming levels to lighting circuits. This communication code is simply a method of representing dimming levels for a lighting circuit so that the power line receiver can translate this information into the appropriate dimming level signal. The desired dimming level being communicated by the power line controller is embedded in the control signal as a signal pattern that is associated with the desired dimming level. 
     To insert the control signal on the AC power signal, the power line controller has a transformer coupled to the signal pattern circuit. The secondary winding of this transformer is connected in series with the AC power line to insert the control signal on the AC power signal. 
     A high frequency series resonant filter is coupled across the AC main input lines. A resonant frequency of the filter is tuned to the frequency of the control signal wherein an impedance of the filter at the control signal frequency is close to zero, thereby effectively preventing the control signal from feeding back to the AC main lines or other loads that are coupled to the same AC main lines. 
     This AC power signal is then transmitted to the lighting circuit(s). To extract the control signal out of the AC power signal, a power line receiver has a resonant circuit connected in parallel with the AC power line. The resonant circuit should be tuned to transmit the control signal and to filter out the AC power signal. A dimming level sensing circuit then senses the signal pattern on the control signal and generates a dimming level signal corresponding to the desired dimming level. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of the power line communication system as disclosed herein. 
         FIG. 1A  is a frequency domain graph showing a frequency bandwidth of one embodiment of the control signal, a frequency bandwidth of one embodiment of the AC power signal, and a bandwidth of transmission for one embodiment of the resonant circuit. 
         FIG. 2  is a circuit diagram of one embodiment of the power line controller as disclosed herein. 
         FIG. 3  is an illustration of two graphs related to signals created by the power line controller shown in  FIG. 2 . The top graph in  FIG. 3  is a time domain illustration of the dimming level information signal generated by a switch pattern circuit of the power line controller. The bottom graph in  FIG. 3  is a time domain illustration of an AC power signal for powering a lighting circuit after the power line controller has inserted a control signal on the AC power signal. 
         FIG. 4  is a circuit diagram of one embodiment of the power line receiver coupled to a lighting circuit. 
         FIG. 4A  is a time domain illustration of the control signal after it has been extracted from the AC power signal by the power line receiver shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring generally to  FIGS. 1-4A , various exemplary embodiments of an invention may now be described in detail. Where the various figures may describe embodiments sharing various common elements and features with other embodiments, similar elements and features are given the same reference numerals and redundant description thereof may be omitted below. 
     Referring now to  FIG. 1 , an embodiment of a power line communication system  10  communicates a desired dimming level to one or more lighting circuits  12  over AC power lines  14 A,  14 B. Power line controller  16  controls the lighting circuit  12  so that the lighting circuit  12  dims an associated lighting device  18  in accordance with a desired dimming level. A “lighting circuit” in accordance with the present invention may, unless otherwise stated or as required for the purposes of a specific application, be understood to encompass either or both of an electronic ballast for regulating output AC power to a lamp or an LED driver for regulating output DC power to an LED array. 
     To control the lighting circuit  12 , the power line controller  16  inserts a control signal  20  on an AC power signal  22  transmitted over the AC power lines  14 A,  14 B. Power line receiver  24  receives the AC power signal  22  and extracts the control signal  20 . Power line receiver  24  then generates a dimming level signal  28  corresponding to the desired dimming level. This dimming level signal  28  may be received by a control circuit  26  that controls the power output from the lighting circuit  12 . Using the example of an electronic ballast for the lighting circuit, the control circuit  26  may then adjust the operating frequency of one or more switching elements in a ballast inverter circuit so that the electronic ballast  12  operates at the desired ballast dimming level. 
     The power line communication system  10  may operate by utilizing analog and digital communication codes for communicating dimming levels to lighting circuits. These codes generally associate a particular signal pattern with a particular dimming level. For example, if a digital communication code is used, the signal pattern will represent a series of “ones” and “zeros”. The power line receiver  24  may then translate the signal pattern into a digital word corresponding to a particular dimming level to produce the appropriate dimming level signal  28 . 
     Referring now to an embodiment as represented in  FIGS. 1 and 1A , the control signal  20  may be generated by the power line controller  16  to be within a particular frequency bandwidth  34 . The frequency bandwidth  34  of the control signal  20  should be outside a frequency bandwidth  36  of the AC power signal  22 . Theoretically, the AC power signal  22  may be represented as a Kronecker delta in the frequency domain and therefore has an infinitely thin frequency bandwidth  36 . In practice, however, the frequency bandwidth  36  of the AC power signal  22  will have a measureable bandwidth.  FIG. 1A  illustrates that the center frequency  34 A of the control signal  20  is typically 15 kHz or higher. The power line receiver  24  may have a resonant circuit  38  with a response curve  38 A that has a bandwidth  40  outside the bandwidth  36  of the AC power signal  22 . The bandwidth  34  of the control signal  20  however may typically be within the bandwidth  40  of the response curve  38 A of the resonant circuit  38 . This permits the power line receiver  24  to receive the control signal  20  and to filter out the AC power signal  22 . 
     Bandwidth is generally defined as a range of frequencies in which the frequency signal components of a signal or the response curve of the circuit are above an amplitude threshold. The standard amplitude threshold for defining bandwidth is typically half of the maximum value of the signal or −3 decibels. However, the meaning of bandwidth for this application is not limited to half the maximum value or −3 decibel threshold. The bandwidth of interest should correspond to the particular embodiment implemented. For example, if the control signal  20  is particularly flat in the frequency domain so to include a significant amount of signal components away from a center frequency, the bandwidth  34  of the control signal  20  may be defined by a higher amplitude threshold to compensate for signal components which may be above or near to the −3 decibel threshold. Conversely, if the control signal is particularly narrow, it may be advantageous to lower the amplitude threshold that defines the bandwidth  34  of the control signal  20  which would require a less sensitive resonant circuit  38 . 
     Referring again to the embodiment of  FIG. 1  and  FIG. 1A , the resonant circuit  38  is connected across the AC power lines  14 A,  14 B. By connecting the resonant circuit  38  in parallel with the AC power lines  14 A,  14 B, the power line receiver  24  is able to detect the control signal  20  even if it is relatively weak. The connection of the resonant circuit  38  across the AC power lines  14 A,  14 B provides the power line receiver  24  with a detector with a high Q factor. This high Q factor allows the resonant circuit  38  to resonate with high amplitude near the resonant frequency  38 B. Consequently, the resonant circuit  38  may be configured to have a resonant frequency  38 B as close as possible to the center frequency  34 A of the control signal  20 . Theoretically, the resonant frequency  38 B is chosen to be equal to the center frequency  34 A of the ballast control signal  20 . This parallel-coupled resonant circuit  38  provides for high noise immunity and permits the signal level of the control signal  20  to be relatively low. 
     Referring now to  FIG. 2  and  FIG. 3 , the operation of one embodiment of the power line controller  16  is described. In the example shown, a power line controller  16  is positioned between an AC input V_AC_IN and a first set of one or more loads  12 , whereas the same AC input may further be provided to one or more additional loads or sets of loads  12   a , for which additional power line controllers (not shown) may be provided. Power line controller  16  has a signal pattern circuit  43  that produces a dimming level information signal  42  with a signal pattern  44  ( FIG. 3 ) that is utilized to communicate the desired dimming level. As mentioned above, codes may be utilized to transmit information on the AC power signal  22 . The signal pattern  44  of the dimming level information signal  42  may be generated in accordance with one of these codes. 
     For example, the embodiment of the power line controller  16  illustrated in  FIG. 2  has a signal pattern circuit  43  that generates the dimming level information signal  42  in accordance with a digital high frequency injection scheme. The signal pattern  44  of the digital high frequency injection scheme is a series of high frequency pulses  44 A that represent a series of bits. To illustrate, the presence of a high frequency pulse  44 A during a particular time interval  45  of the dimming level information signal  42  may represent a “one” while the absence of a high frequency pulse  44 A during a particular time interval may represent a “zero”. This series of bits represents the desired dimming level. 
     To generate the series of high frequency pulses  44 A, the signal pattern circuit  43  has a high frequency signal production circuit  46  that generates a high frequency signal  47 . The frequency of the high frequency signal  47  should be higher than the frequency of the AC power signal  22 . In the illustrated embodiment, the AC power signal  22  operates at 50 Hz to 60 Hz while the frequency of the high frequency signal  47  is greater than 154 kHz. 
     A primary winding  50  of transformer TX_ 1  is coupled to the signal pattern circuit  43 . Output terminals  54 A,  54 B of the power line controller  16  should be configured to connect the secondary winding  54  in series with AC power line  14 B. High frequency pulses  44 A are created by opening and closing the switch  48  which is coupled to the high frequency signal production circuit  46  and the transformer TX_ 1 . Transformer, TX_ 1 , may isolate signal pattern circuit  43  from the AC power signal  22  to protect the circuit. Switch  48  couples the high frequency signal  47  to the transformer TX_ 1  when the switch  48  is closed and suspends the transmission of the high frequency signal  47  to the transformer TX_ 1  when the switch  48  is open. By timing the opening and closing of switch  48 , the signal pattern  44  of the dimming level information signal  42  represents the desired dimming level through the series of high frequency pulses  44 A. 
     The control signal  20  is inserted on the AC power signal  22  and is associated with the dimming level information signal  42 . The control signal  20  may be the dimming level information signal  42 . The power line receivers and AC power systems may be designed to be robust enough to receive and process a dimming control signal  20  as simply being itself the dimming level information signal  42 . However, dimming level information signal  42  may have characteristics that are disadvantageous for transmission over the AC power lines  14 A,  14 B. If so, certain components may be included so that the power line controller  16  inserts a suitable control signal  20  on the AC power signal  22 . 
     For example, a high frequency signal bypass filter may be connected between the AC power lines  14 A,  14 B to prevent high frequency components in the control signal  20  from being reflected on the AC power lines,  14 A,  14 B. In one embodiment, a series resonant circuit is formed of components C_res and L_res and connected in parallel with filtering capacitor C 2 . The resonant frequency of this resonant filter may be designed at the control signal frequency so that the impedance of this resonant filter at the signal frequency is close to zero, or in other words the components for the resonant circuit may be selected in view of the signal frequency f_ctl that the power line controller is transmitting according to the equation: 
               f   ctl     =       1     2   ·   π   ·         L   res     ·     C   res             .           
In this manner the control signal will be bypassed or shorted before it reaches the power supply V_AC_IN. This approach may effectively prevent high frequency components in the control signal  20  from being reflected on the AC power lines,  14 A,  14 B.
 
     A DC filter may further be coupled between the signal pattern circuit  43  and the transformer Tx_ 1  to filter out DC signal components from the dimming level information signal  42 . This prevents DC signal components from being transmitted over the AC power lines  14 A,  14 B. Transformer Tx_ 1  may also affect the characteristics of the dimming level information signal  42 , such as the voltage and current amplitudes of the control signal  20 . The power line controller  16  may also have additional equipment for manipulating the timing, frequency characteristics, or shape of the signal pattern  44  on the control signal  20  in accordance with the particular characteristics required by the power line receiver. 
     Secondary winding  54  of transformer Tx_ 1  may connect in series with AC power line  14 B to insert the control signal  20  on the AC power signal  22 . However, power line controller  16  may connect to either AC power line  14 A,  14 B to insert the control signal  20  on the AC power signal  22 . The series connection of secondary winding  24  allows the power line controller  16  to insert what may be a relatively weak control signal  20  on AC power signal  22 . 
     In the illustrated embodiment, switch control circuit  56  in the signal pattern circuit  43  opens and closes the switch  48  to generate the signal pattern  44 . This switch control circuit  56  receives a dimming level input signal  58  to determine the desired dimming ballast level which is to be communicated over the AC power lines  14 A,  14 B. Dimming level input signal  58  may be a digital signal that represents the desired dimming level or may be an analog signal such as a DC signal whose DC level represents the desired dimming level. 
     In either case, switch control circuit  56  translates this information into the appropriate signal pattern  44 , for transmitting the desired dimming level and opens and closes the switch  48  accordingly. Switch control circuit  56  may thus store or receive information about dimming level codes to produce the appropriate dimming level information signal  42 . In addition, if the dimming level input signal  58  is a digital signal then the switch control circuit  56  may simply cause the switch  48  to open and close and create a signal pattern  44  of ones and zeros in accordance with the “ones” and “zeros” of the digital signal. 
     In contrast, if the power line receiver is not equipped to translate the digital format of the dimming level input signal  58 , the switch control circuit  56  may translate the dimming level input signal into the appropriate digital format for the desired dimming level and generate a signal pattern  44  in accordance with this format. 
     If the dimming level input signal  58  is an analog signal, then the switch control circuit  56  may associate the signal level of the dimming level input signal  58  with the desired dimming level and open and close the switch  48  accordingly. Once the control signal  20  has been inserted on the AC power signal  22 , the AC power signal  22  is transmitted over the AC power lines  14 A,  14 B to power one or more load or lighting circuits  12 . The illustrated embodiment generates a control signal  20  having the series of high frequency pulses  44 A in the dimming level information signal  42 . The AC power signal  22  is shown in the bottom graph in  FIG. 1A  after having been inserted with control signal  20 . High frequency pulses  44 A have been inserted on the AC power signal  22  for communication to a power line receiver. 
     Referring now to  FIG. 1A ,  FIG. 4 , and  FIG. 4A , the operation of one embodiment of the power line receiver  24  that receives AC power signal  22  with control signal  20  is shown and described. The power line receiver  24  shown in  FIG. 4  is integrated into the lighting circuit  80 . Input terminals TAR, TBR are configured so that when the power line receiver  24  is connected to AC power line  14 B, resonant circuit  38  is connected in parallel with the AC power lines  14 A,  14 B. Resonant circuit  38  of the power line receiver  24  is shown as a series resonant circuit having capacitor C_r and the primary winding  60  of transformer Tx_r. This resonant circuit  38  should be connected to the AC power line  14 B in front of the electromagnetic interference filter  63  in the lighting circuit  80  to avoid distortion of the control signal  20 . Transformer Tx_r thus acts to isolate the power line receiver  24  from the power line  14 B and also is part of a resonant circuit  38  for receiving the ballast control signal  20 . 
     The resonant frequency of the resonant circuit  38  may preferably be designed at the control signal frequency f_ctl to provide great selectivity and gain: 
               f   ctl     =     1     2   ·   π   ·         TX   r     ·     C   r                   
Furthermore, this series resonant circuit improves noise immunity by being connected in parallel with the AC main, as the noisy input current going into the ballast or driver does not pass through the signal receiver circuit. This may provide the additional benefit of minimizing the size of the transformer Tx, which otherwise may have to account for such a large input current.
 
     As explained above, resonant circuit  38  extracts the control signal  20  from the AC power signal  22  and transmits the control signal  20  to secondary winding  64  of transformer TX_r which is connected to a dimming level sensing circuit  66 . As illustrated in  FIG. 2 , the bandwidth  34  of the control signal  20  is within the bandwidth  40  for the response curve  38 A of the resonant circuit  38 . 
     The dimming level sensing circuit  66  senses the signal pattern  68  on the control signal  20  and generates a dimming level signal  72  corresponding to the desired dimming level. In the illustrated embodiment, signal pattern  68  is formatted according to a high frequency digital communication code. Each “one” or “zero” is represented by the presence or absence of a high frequency pulse  68 A during a time interval  68 B of the control signal  20 . Dimming level sensing circuit  66  receives the control signal  20  at signal pattern decoder circuit  70  which is operable to convert the signal pattern  68  into a digital signal  74  representing the desired dimming level. Signal pattern decoder circuit  70  is thus equipped with an analog-to-digital converter capable of sensing a high frequency pulse  68 A and creating a digital signal  74  in accordance with the transmitted signal pattern  68  of the control signal  20 . Dimming signal production circuit  76  receives digital signal  74  and is operable to generate the dimming level signal  72  corresponding to the desired dimming level based on the digital signal  74 . 
     Dimming level signal  72  may then be transmitted to a control circuit  76  that controls the switch frequency of a power converter  78  for the lighting circuit  80 . In this embodiment, dimming level signal  72  is a DC signal having a signal level corresponding to the desired dimming level. Inverter control circuit  76  utilizes the dimming level signal  72  as a reference signal and compares the reference signal with a signal from the power converter  78  or lighting device. A switch frequency of the power converter  78  is adjusted to produce an output signal  82  to the lighting device in accordance with this comparison. The power consumed by lighting device  84  is thus adjusted in accordance with the dimming level signal  72 . Dimming signal production circuit  76  may thus be configured with a digital-to-analog converter that receives the digital signal  74  and converts that digital signal  74  into the dimming level signal  72 . 
     Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” may include plural references, and the meaning of “in” may include “in” and “on.” The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. 
     The term “coupled” means at least either a direct electrical connection between the connected items or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means at least either a single component or a multiplicity of components, either active and/or passive, that are coupled together to provide a desired function. Terms such as “wire,” “wiring,” “line,” “signal,” “conductor,” and “bus” may be used to refer to any known structure, construction, arrangement, technique, method and/or process for physically transferring a signal from one point in a circuit to another. Also, unless indicated otherwise from the context of its use herein, the terms “known,” “fixed,” “given,” “certain” and “predetermined” generally refer to a value, quantity, parameter, constraint, condition, state, process, procedure, method, practice, or combination thereof that is, in theory, variable, but is typically set in advance and not varied thereafter when in use. 
     The terms “switching element” and “switch” may be used interchangeably and may refer herein to at least: a variety of transistors as known in the art (including but not limited to FET, BJT, IGBT, IGFET, etc.), a switching diode, a silicon controlled rectifier (SCR), a diode for alternating current (DIAC), a triode for alternating current (TRIAC), a mechanical single pole/double pole switch (SPDT), or electrical, solid state or reed relays. Where either a field effect transistor (FET) or a bipolar junction transistor (BJT) may be employed as an embodiment of a transistor, the scope of the terms “gate,” “drain,” and “source” includes “base,” “collector,” and “emitter,” respectively, and vice-versa. 
     The terms “power converter” and “converter” unless otherwise defined with respect to a particular element may be used interchangeably herein and with reference to at least DC-DC, DC-AC, AC-DC, buck, buck-boost, boost, half-bridge, full-bridge, H-bridge or various other forms of power conversion or inversion as known to one of skill in the art. 
     Terms such as “providing,” “processing,” “supplying,” “determining,” “calculating” or the like may refer at least to an action of a computer system, computer program, signal processor, logic or alternative analog or digital electronic device that may be transformative of signals represented as physical quantities, whether automatically or manually initiated. 
     The terms “controller,” “control circuit” and “control circuitry” as used herein may refer to, be embodied by or otherwise included within a machine, such as a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed and programmed to perform or cause the performance of the functions described herein. A general purpose processor can be a microprocessor, but in the alternative, the processor can be a microcontroller, or state machine, combinations of the same, or the like. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     The previous detailed description has been provided for the purposes of illustration and description. Thus, although there have been described particular embodiments of a new and useful invention, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.