Abstract:
A point-to-point communications system ( 20 ) for transmitting messages from any location (A) within a power distribution system or network ( 10 ) to any other location (B) within the network. A transceiver ( 12 ) at the one location includes a transmitter (X) that impresses a waveform (W R ) on a waveform (W G ) propagated by the network to supply power throughout the network. The transmitter is a resonant transmitter that includes a reactive load ( 13 ) which is selectively connected to and disconnected from the power distribution network. A controller ( 16 ) controls operation of the transmitter to connect and disconnect the reactive load from the network so to impress on the propagated waveform a dampened sinusoidal waveform whose characteristics represent information conveyed over the power distribution system. A receiver (Yn) at the other location receives and demodulates the dampened sinusoidal waveform to extract therefrom the information being conveyed by it.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. patent application Ser. No. 61/182,483 filed May 29, 2009, which is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to communications sent through a power distribution network; and, more particularly, to a point-to-point communications system by which information is readily transmitted from any one location within the power distribution network to any other location within the network. 
         [0003]    Power line communications systems are known in the art. A typical system enables a utility to send messages over its power line to or from a central location such as a sub-station to most, if not all, of its customers connected to that site. The messages involve such things as current electrical usage at the customer&#39;s site, polling requests to determine whether or not an outage has occurred within a service area, or commands to reduce or shut-off the amount of power provided to a load at the customers site during periods of peak electrical usage. Replies received from the various locations to which messages are sent enable the utility to determine its current operational status, as well as changes that may need to be made to reconfigure the power distribution system for changes (or prospective changes) in its operating circumstances. 
         [0004]    Electrical usage has grown significantly in recent years so that, over time, the demands placed on utilities has greatly increased and many utilities are now hard pressed to maintain adequate levels of service to their customers. Similarly, the demands placed on current communications systems employed by these utilities to support their operations have also greatly increased to the point where it has become difficult for these systems to timely provide the information necessary for the utility to operate at the level at which it needs to operate. For example, the amount of information required by the utility, on an almost continuous basis, has expanded to the point where the information throughput (data transmission rates) required of communications systems is at, or near the limits of the communications system&#39;s capabilities. 
         [0005]    Installing, maintaining, and upgrading these communication systems is both time consuming and expensive. Some systems require, for example, routers, repeaters, or boosters spaced at intervals throughout the power distribution network to insure that a sufficient signal level is maintained that the transmitted information can be recovered at the receiving end. In addition, operation of some systems produces undesirable side effects which can be annoying to customers of a utility. 
         [0006]    The present invention is directed to a point-to-point communications system that addresses these and other problems of existing communication systems. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    What is described in the present disclosure is a point-to-point communications system particularly for use with a utility&#39;s power distribution network to send communications from any one location in the network to any other location in the network. 
         [0008]    The communications system uses transceivers located throughout the network for sending and receiving messages. The transmitter portion of a transceiver comprises a resonant transmitter having a capacitor and inductor whose values enable the transmitter to generate a dampened sinusoidal waveform of a predetermined frequency. Generation of the waveform is controlled to provide a modulated waveform which propagates through the power distribution network in the presence of the main waveform generated by the utility. Among the modulation methods employed in the point-to-point communications system are on-off keying (OOK), phase shift keying (PSK), and quadrature amplitude modulation (QAM). A receiver portion of the transceiver receives the dampened sinusoidal waveform on some, or all three, phases (φ) of the network. The receiver combines the received signals and processes the result to obtain a transmitted message. 
         [0009]    The transceivers can be a single unit, or the transmitter and receiver portions of a unit may be separate pieces of equipment. Further, either section of a transceiver can be selectively deactivated by the user of the system. 
         [0010]    The point-to-point communications system herein described presents significant advantages over conventional systems. For example, the resonant transmitter portion of the transceiver utilizes a reactive rather than a resistive load; and as a result, heat dissipation requirements are low. Another significant advantage is that the system of the present invention requires relatively little equipment to install and operate, and eliminating unnecessary equipment significantly lowers the cost to install, maintain, and repair the communications system. In addition, unwanted side effects caused by operation of some systems are eliminated. 
         [0011]    Another advantage of the communications system of the present invention is that higher data transmission rates are achievable than with current systems because transmitted signals include more bits per symbol. Also, digital modulation schemes not practical for use in conventional communications systems, can now be readily employed. In addition, the ability to provide higher data transmission enables security protocols unusable in conventional systems to also be readily employed so to better protect transmissions. 
         [0012]    It is a further advantage of the system that the dampened sinusoidal signal produced by a transceiver can be transmitted through the multiple voltage levels which occur within the network, both without the need of additional equipment, and without significant signal degradation. 
         [0013]    In another embodiment of the invention, code division multiple access (CDMA) techniques are employed to better improve data transmission. 
         [0014]    Other objects and features will be apparent or pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0015]    The objects of the invention are achieved as set forth in the illustrative embodiments shown in the drawings which form a part of the specification. 
           [0016]      FIG. 1  is a simplified schematic of a point-to-point communications system incorporated into a utility&#39;s power distribution network; 
           [0017]      FIG. 2  is a schematic of a transmitter portion of a transceiver of the communications system; 
           [0018]      FIG. 3  is a block diagram of a receiver portion of the transceiver; 
           [0019]      FIG. 4  illustrates the generation of a dampened sinusoidal waveform using on-off keying (OOK); 
           [0020]      FIG. 5  illustrates generation of the dampened sinusoidal waveform using phase-shift keying (PSK); 
           [0021]      FIG. 6  is a simplified representation of a power distribution system; 
           [0022]      FIGS. 7A-7C  illustrates operation of a resonant transmitter to generate the dampened sinusoidal waveform for transmission through the utility&#39;s power distribution network together with the waveform propagated by the utility so to convey information from one location in the power distribution system to another; and, 
           [0023]      FIG. 8  illustrates generation of a dampened sinusoidal waveform using amplitude modulation. 
       
    
    
       [0024]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF INVENTION 
       [0025]    The following detailed description illustrates the invention by way of example and not by way of limitation. This description clearly enables one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. Additionally, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it will be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
         [0026]    Referring to the drawings, a power distribution system or network is indicated generally  10  in  FIG. 6 . The network includes a power generator G from which power is distributed through a plurality of substations S 1 -S N  and over power lines L 1 -Ln routed from each substation to the facilities F of residential, commercial, and industrial consumers. Overlying network  10  is a point-to-point communications system of the present invention which is indicated generally  20  in  FIG. 1 . Point-to-point communications system  20  enables messages to be transmitted from any one location A within the power distribution system to any other location B within the system. Typically, messages are sent from a substation S to one or more of the facilities F and a reply message is separately sent from each facility back to the substation. It is a feature of the present invention, however, that a message can be sent from locations other than a substation to any other location (which could be, but is not necessarily a substation) within communications system  20 . 
         [0027]    As shown in  FIG. 1 , a voltage waveform W G  generated or propagated by the utility is impressed across the primary windings of a high voltage transformer T HV . Waveform W G  is typically a 3φ, 240 VAC, 60 Hz waveform; although it will be understood by those skilled in the art that communications system  20  works equally as well with other utility generated waveforms, for example, 120 VAC, 60 Hz waveforms, and the 50 Hz waveforms generated by utilities in many countries. The secondary windings of transformer T HV  are, in turn, connected across the primary windings of transformers T 1 -T N . A transmitter X 1  of a transceiver indicated generally  12  is connected across the secondary or low voltage windings LV of transformer T 1  at location A; while a receiver section Y 1  of transceiver  12  is coupled to the power line for receiving and processing messages sent over communications system  20 . At location B, a transceiver  13  includes a transmitter Xn connected across the low voltage windings of transformer T n , with a receiver Yn of transceiver  13  being connected to the power line for receiving and processing messages sent over the communications system. 
         [0028]    Referring to  FIG. 2 , transmitter X 1  includes a reactive load  13  comprised of an inductor L and a capacitor C. The values of the capacitor and inductor are chosen so transceiver  12  resonates at a desired frequency. Reactive load  13  is connected, through a switch  14 , across a drain resistor R D . Transmitter X 1  is a resonating transmitter which, as shown in  FIGS. 4 and 5 , produces a dampened sinusoidal or ringing waveform W R  which is now transmitted through the power distribution system together with propagated waveform W G  to convey, via the resulting waveform W M , information (i.e., commands or instructions, query responses, data, etc.) from location A to location B. For this purpose, switch  14  is operated in a controlled manner by a digital controller  16 . In operation, controller  16  controls operation of transmitter X 1  such that the characteristics of the dampened sinusoidal waveform represent the information being conveyed through the power distribution network by the resulting, modulated waveform. 
         [0029]    Referring to  FIGS. 7A-7C , controller  16  operates switch  14  in the following sequence: 
         [0030]    First, as shown in  FIG. 7A , controller  16  connects reactive load  13  of transmitter X 1  to the low voltage (LV) side of transformer T 1  through switch  14 , while drain resistor R D  is isolated from both the reactive load and the transformer. This produces the dampened sinusoidal waveform W R  such as shown in  FIGS. 4 and 5 . 
         [0031]    Next, as shown in  FIG. 7B , controller  16  operates switch  14  to isolate the reactive load and the drain resistor both from transformer T 1  and from each other. Isolating both the reactive load and drain resistor from transformer T 1  results in capacitor C holding its charge at a first predetermined charge level. 
         [0032]    As shown in  FIG. 7C , controller  16  now operates switch  14  to isolate reactive load  13  from transformer T 1 , while placing drain resistor R D  across the reactive load. This now provides a path to drain off charge from capacitor C. 
         [0033]    Finally, controller  16  operates switch  14  to again isolate both the reactive load and drain resistor from transformer T 1  and from each other. Again, this is the circuit configuration shown in  FIG. 7B . This switching now has the effect of letting capacitor C hold or maintain its charge at a second predetermined level. 
         [0034]    Alternately, drain resistor R D  may be omitted. When this done, the switching sequence is  FIG. 7A-FIG .  7 B for each signal, rather than the previously described sequence of  FIG. 7A-FIG .  7 B- FIG. 7C-FIG .  7 B. However, the amplitude of signals as shown in  FIGS. 4 and 5  will now vary from signal to signal. This is because in the previously described embodiment, drain resistor R D  acted to regulate the amplitude of the signal by resetting the resonator initial conditions. 
         [0035]    Controller  16  implements a variety of algorithms by which encoded bits representing data, instructions, etc. are sent from the one location to the other. In this regard, controller  16  utilizes a variety of channel coding schemes including, for example, a low-density parity-check (LDPC) code. 
         [0036]    For OOK, and as shown in  FIG. 4 , the controller implements an algorithm by which switch  14  is operated such that one bit is transmitted for each half-cycle of the waveform W G  impressed across the low voltage side of transformer T 1 . In operation, the generation of a resonant pulse waveform during a half-cycle of waveform W G  represents a binary 1; while the absence of a resonant pulse waveform represents a binary 0. Appendix A, which is attached hereto and is incorporated herein by reference, sets forth the mathematical formulations used for OOK modulation. 
         [0037]    Bits comprising the message to be sent from location A to location B are provided as inputs to controller  16  as shown in  FIG. 2 . If a binary 1 is to be transmitted, then a resonant pulse waveform is imposed on the generated waveform beginning at a time t 1  shown in  FIG. 4 , and ending at a time t 2 . For this purpose, the algorithm implemented by controller  16  includes a phase locked loop (PLL)  18  which synchronizes timing of the resonant pulse waveform (i.e., the binary symbol) with the voltage impressed across the LV windings of transformer T 1 . 
         [0038]    Times t 1  and t 2  are adaptively computed using the algorithm, and the results of these computations control switching of switch  14  by controller  16 . That is, they control cycling of switch  14  from its holding position shown in  FIG. 7B  to the conducting position shown in  FIG. 7A , and then back to the holding position. For this purpose, feedback signals are supplied to controller  16  by the algorithm for use in calculating the respective modulation start and finish times. This level of operational control further has the advantage of minimizing heat dissipation and reducing or eliminating spurious electromagnetic emissions. The feedback is provided by a voltage measurement V T  taken across the LV windings of transformer T 1 , and a voltage measurement V C  taken across capacitor C. The voltage measurements are applied to respective analog-to-digital (ND) converters  22 ,  24  whose digital outputs are supplied to controller  16 . 
         [0039]    Further referring to  FIG. 4 , the algorithm also adaptively computes the times t 3  and t 4 . These times determine when controller  16  operates switch  14  so that the switch is switched from the holding position shown in  FIG. 7B  to its position shown in  FIG. 7C  in which capacitor C is discharged, and then back to the holding position of  FIG. 7B . 
         [0040]    Besides providing OOK, controller  16  also implements an algorithm for PSK. For this type modulation, switch  14  is operated by the algorithm so as to modulate the waveform W G  impressed across the LV windings of transformer T 1  with one or more data bits during each interval of modulation. This produces transmissions having higher data rates than OOK. This is as shown in  FIG. 5 . When PSK is used by controller  16 , spectral analysis of signals V T  and V C  is used to compute the time t 1  when reactive load  13  is connected to the low voltage windings of transformer T 1  and the time t 2  when it is disconnected. This is accomplished by cycling switch  14  as previously described. The result is a discrete phase shift in the resonant pulse sinusoid. Again, Appendix A sets forth the mathematical formulations used for PSK modulation. 
         [0041]    In another embodiment, controller  16  implements an algorithm for amplitude modulation (AM). Those skilled in the art will understand that still other modulation techniques may be employed without departing from the scope of the invention. Regardless of the modulation technique employed, those skilled in the art will further understand that the characteristics of dampened sinusoid W R  represents the information being conveyed over the power distribution system by the resulting modulated waveform. 
         [0042]    In this embodiment, and referring to  FIG. 8 , amplitude modulation is achieved by changing the duration, and thus the energy, of the transmitted signals. Accordingly, the signals “00” and “10” are shown in  FIG. 8  to have a greater amplitude than the other signals “01” and “11”. The signals “00” and “10” therefore are allowed to resonate for a longer period of time; while, the signals “01” and “11” which are lower energy signals resonate for a shorter period of time. Controlled on/off switching is used, as in PSK modulation to control the sign. Importantly, amplitude modulation and PSK can be combined to implement quadrature amplitude modulation (QAM) and thus facilitate greater rates of data transmission. Large symbol constellations are generated by changing both switch-on and switch-off times. 
         [0043]    In addition to these techniques, the method of the present invention further utilizes code division multiple access (CDMA) in combination with OOK, PSK, or QAM in order to further improve data transmission by facilitating multiple transmitter access to a communications channel. 
         [0044]    Receiver Y 1  of transceiver  12  is, for example, a multiple input digital receiver. As shown in  FIGS. 1 and 3 , the receiver is connected across the medium voltage MV or low voltage LV lines of one or more of the phases using respective couplers  26  or  27 . Coupler  26  is, for example, a current transformer and coupler  27  a voltage transformer. Importantly, coherently collecting the signals on all the phases of power distribution network  10 , and combining and processing them, improves the fidelity of the communications sent and received using system  20 . 
         [0045]    Each input to a receiver Y is first supplied to an ND converter  28 . In  FIG. 3 , these are shown to be connected in parallel. Importantly, receiver Y is capable of detecting and demodulating received transmissions without communications system  20  needing to use signal boosters or other ancillary equipment typically used in conventional communications systems so transmitted signals are capable of being detected. This significantly simplifies the communications process, allows for a less costly system because fewer components are required to affect communications throughout the utility&#39;s power distribution network, and also reduces costs because of the reduced amount of equipment maintenance and repair that is involved in operating communications system  20 . 
         [0046]    Digital signal outputs from the converters are provided as inputs to a signal processor  30  of the receiver which includes a PLL  32  that synchronizes the received signals with a transmitted clock signal. In this regard, every z th  symbol transmitted by transceiver  12  at location A comprises a pilot symbol that receiver Yn at location B “knows” to expect. The algorithm used by receiver Yn now performs an adaptive equalization of received transmissions using these transmitted pilot symbols. Processor  30  then further implements the algorithm to demodulate both OOK and PSK transmissions, as well as, for example, decoding LDPC encoded communications. The decoded message is provided as an output by the receiver to an electric meter or other device at a facility F which is responsive to communications sent through system  20 . 
         [0047]    What has been described is a point-to-point communications system implemented in a utility&#39;s power distribution network by which communications are sent from anywhere within the network to anywhere else in the network. The resonant transmitter used by the communications system provides a greater data transmission capability (throughput) than conventional communications systems. The point-to-point communications system also provides greater signal clarity, eliminates RFI and light flicker problems associated with conventional communications systems, and does so while not requiring ancillary equipment such as boosters, repeaters, and the like, so to provide a rapid, high quality communications capability for a utility. 
         [0048]    In view of the above, it will be seen that the several objects and advantages of the present disclosure have been achieved and other advantageous results have been obtained.