Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B3/00—Line transmission systems
  • H04B3/54—Systems for transmission via power distribution lines

Definitions

• This invention relates to communications over a power distribution network to, for example, supply electricity from a utility to consumers. More particularly, the invention is directed to the simultaneous detection of communications signals, specifically those sent from consumer facilities back to the utility, on all phases of the utility's power distribution network.
• Communications systems employed by electrical utilities are known in the art. See for example, U.S. patents 6,940,396 and 5,262,755.
• the utility uses the system to send messages or commands (outbound signals) from a transmitter location (usually at a network substation) to consumer facilities.
• a transceiver which is typically incorporated in meters at the respective facilities, in response to the execution of a command or a request for information, then sends a signal (an inbound signal) back to the utility.
• TWACS® Two-way automatic communications systems
• inbound signal detection hardware only had the capability to sample a signal on one phase at a time.
• Current signal detection hardware now has the capability to sample signals on all inputs (phases) to a substation simultaneously.
• a method for detection of signals transmitted simultaneously on multiple phases is disclosed in U.S. Patent No. 6,940,396, but that method is designed for detecting signals on one phase at a time and relies on temporal differences between signals to separate them.
• all inbound signals appear on at least two of the three phases (or four phases if a neutral phase is present) available at the substation, and optimal detection of inbound signals should therefore include signals from these multiple phases.
• Using the method of the invention for performing "all-phase" detection, and which operates in a concurrent phase mode it now is.
• the signal-to-noise ratio (SNR) of a combined signal In addition to all-phase detection producing a higher signal strength signal, optimizing the signal-to-noise ratio (SNR) of a combined signal also requires that the detection method take into account correlation, if present, in the noise signals on the various phases.
• the signal strength and noise correlations are estimated adaptively for each inbound signal and the resulting combining scheme should produce higher signal-to-noise ratios.
• the present invention is directed to an all-phase detector and detection method for use in a communications system for a utility's power distribution network.
• the detector and method detect the signal present on all three (or four) phases of the network, and combines the results from all phases to produce a signal having a higher signal strength than any of the individual signals.
• the detector and method further have the effect of suppressing noise whose statistics are uncorrelated across more than one of the phases.
• the algorithm finds optimal weights for summing the signals such that signal power is increased and noise is suppressed to the extent possible to maximize the signal-to-noise ratio.
• the method of the invention utilizes a concurrent-phase algorithm which integrates the previously separate signal-processing algorithms for signal detection and for cancellation of interference from signals on other phases. This integration results in a less complex and more reliable detector design. Further, all additional signals present on the neutral conductor are used in the algorithm of the present invention thereby eliminating the previous practice of having to retry missed communications on the neutral conductor.
• the detector is readily implemented in current utility communications systems such as TWACS so as to provide better communications between the utility and its customers with respect to inbound signals sent from a customer's site to a utility substation.
• Fig. 1 is a simplified block diagram of a data processing stream for single-phase signal detection
• Fig. 2 is a simplified block diagram of a data processing stream for all-phase signal detection
• Fig. 3 is a representation of a windowing scheme used for all-phase signal detection.
• Fig. 4 is a graph representing a performance comparison of an all-phase detector and method of the present invention in a concurrent phase mode with the single phase in both single and concurrent phase modes.
• Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
• a sampled current waveform is first processed with a band-pass filter to reduce noise occurring at frequencies having little signal power.
• the filtered waveform is passed through a channel separation filter (such as that shown in U.S. Patent No 5,262,755 which is owned by the same assignee as the current application).
• This filter includes one filter for each channel and is used to process the signal and to isolate the summed pulse shape for each bit from the combined signal. Accordingly, for each channel, a set of waveforms for each bit is produced.
• M is the number of samples per half-cycle and N is the number of bits.
• M is the number of samples per half-cycle
• N is the number of bits.
• the number of samples per half-cycle would be 36 for a 60 Hz AC waveform sampled at the rate of 4320 samples per second, but can be fewer if down sampling is done or a different sample rate is used.
• Signals for all six channels then pass through an outbound signal cancellation algorithm.
• the concurrent phase mode described in previously referred to U.S. Patent No. 6,940,396 and currently used in TWACS systems has outbound transmissions on the phase simultaneous with inbound signals on other phases.
• This algorithm uses the outbound bit pattern, which is known to the detector due to its being generated locally to separate or "clean" the outbound signal from the inbound signal. In cases when no interfering outbound signal is present, the algorithm simply passes the signal through. After this interference cancellation, the resulting signal matrix for each channel is sent to the detector and decoder for the extraction of decoded bits.
• a data processing scheme for all-phase detection is shown.
• the same sequence of steps is performed as is shown in Fig. 1 ; except that now, however, band-pass filtering and channel separation operations are performed on all three phases A, B, and C of the power distribution network.
• the signals from all three phases are combined to create a single "stacked matrix" for each particular channel.
• the outbound cancellation algorithm is then applied to the stacked signal matrices, and these are then passed to the detector and decoder. With signals for each bit being one half-cycle in length, this amounts to 36 samples using the system parameters described earlier.
• Fig. 2 shows phases A, B, and C
• the neutral phase is also included, if it is present.
• the synthetic neutral signal will not necessarily provide any new information when processed using the all-phase detection method of Fig. 2. This is because the signal does not include a different "copy" of the inbound waveform.
• the neutral signal does contain additional inbound signal information not available by summing all of the remaining phases when processing a phase-to-neutral signal. It will be understood by those skilled in the art that noise levels are usually higher at the bus level than at the feeder level.
• the all-phase detection algorithm of the present invention has two significant benefits for a power line communications system. First, is improved performance which is achieved by combining all of the signal sources so to increase the ratio of the detected signal to the noise present on the respective phases. Second, is an improved, simpler system design for concurrent phase detection.
• an external input to the detection algorithm comprises the stacked signal matrix shown on the left side of the Fig.
• this stacked window matrix represents all three phases A, B, and C. Within each phase are three temporal regions representing the main detection window and regions before and after the main window.
• a first step in all-phase detection is to rearrange the single stacked signal matrix into three stacked signal matrices representing each of the three windows. This is as shown on the right side portion of Fig. 3 where the three stacked and windowed matrices are respectively labeled "main window”, "pre-window", and "post-window” signals.
• these three signal matrices are denoted as S ma in, S pre and S pos t- Theoretically, these three matrices do not need to have the same number of columns. However, in simulation tests, reasonably good results were obtained by having them equal. Therefore, for simplicity in the following description, it is assumed that the respective windows are dimensionally equal. This implies that for M samples per phase, each of the windows is M/3 samples wide, and that the three stacked and windowed matrices are of a size M x N, or 4 M/3 x N if a neutral signal is present.
• the multi-phase stacked version of the S ma in samples is again used as the most significant component in the signal detection scheme.
• a singular value decomposition was used to create a low-rank approximation of the main window signal matrix in order to separate signal and noise.
• the rank of the approximation is increased from 3 to 5, this being based on empirical results. This increase is also helpful because the stacked matrix is significantly larger and contains more signal information than does a single phase signal matrix.
• the decoding procedure is, in some respects, similar to a maximum SNR decoding method. That method includes the steps of: a) estimating bits using a correlation detector and a low-rank approximation of a data matrix; and b) refinement of the bit estimate using low-rank approximated data. For all-phase detection, similar steps are used, but with adjustments being made as to the rank and size of the data matrix. The primary difference is in creating an initial estimate of the bits.
• the solution is to apply the correlation detector to both the original and cleaned signal matrices; and then to use the estimated bits from the matrices with the highest signal-to-noise ratio. Simulations have shown this approach to be successful.
• the method of the invention utilizes a low-rank approximation of S ma in to refine the estimate and produce the final result.
• a k is a diagonal matrix containing the first K elements of ⁇ on its diagonal.
• the normalization of A k is not necessary if only one vector is used, as is done with S pre and
• Fig. 4 presents a comparison of the simulated performance of the all- phase detection algorithm of the present invention with two other detection schemes.
• the first scheme of the other schemes is for single-phase signal detection and involves an existing maximum SNR detection algorithm.
• the other scheme is for concurrent- phase detection and is based on line-to-line signaling.
• the concurrent-phase detection algorithm exhibits a slight loss in performance, relative to the single-phase detection algorithm, as a result of increased interference present in the signal.
• the all-phase detection algorithm achieves nearly a 2 dB gain in performance relative to the single-phase signaling detection; and slightly more than a 2 dB gain relative to concurrent-phase signaling detection.
• An exception to this gain in performance is at high SNR where a noise floor exists in the all-phase detection performance. However, since the floor is at a block error rate of less than 10 "3 , it should not cause significant problems for all-phase inbound signal detection.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
• Monitoring And Testing Of Transmission In General (AREA)
• Noise Elimination (AREA)
• Measuring Phase Differences (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

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• 2012
  • 2012-02-28 CA CA2828342A patent/CA2828342C/en active Active
  • 2012-02-28 WO PCT/US2012/026951 patent/WO2012118810A2/en not_active Ceased
  • 2012-02-28 CN CN201280020797.0A patent/CN103548281B/zh active Active
  • 2012-02-28 US US13/407,265 patent/US8761271B2/en active Active
  • 2012-02-28 MX MX2013009921A patent/MX2013009921A/es active IP Right Grant
  • 2012-02-28 JP JP2013556802A patent/JP6106829B2/ja active Active

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