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2017 3rd International Conference on Computer Science and Mechanical Automation (CSMA 2017) ISBN: 978-1-60595-506-3

A Novel Multi-Parallel Power Frequency Communication Technology

Yang WANG

1,2

, Yi-Fan SUN

1

, Yang DONG

1

and Yuan WANG

3,*

1

Tianjin Electric Power Company, State GRID, Tianjin 300010, China

2

Guanghua School of Management, Peking University, Beijing 100871, China

3College of Computer Science and Information Engineering, Tianjin University of Science &

Technology, Tianjin 300457, China.

Email: wangyuan23@tust.edu.cn*

Keywords: Multi-parallel power frequency communication, Power line frequency communication, Smart grid.

Abstract. Power line frequency communication technology using the small distortion about the grid voltage and current waveform to carry information, and cross the transformer remote communication, suitable for line structure and load characteristics in distribution network. It has the advantages of low cost, easy installation, free communication and so on. But the power line frequency communication there is a low rate of defects, and the traditional modulation and demodulation are based on the local voltage zero, because the transceiver system voltage phase difference caused by receiving time domain deviation, which seriously affect the communication performance. This paper established a multi-channel signal transmission model based on the technical mechanism of frequency communication. We use single-phase multi-channel, three-phase transmission, multi-feeder parallel transmission and other means to improve the communication rate, At the same time, this paper based on time-frequency analysis to determine the frequency domain communication signal modulation time domain, combined with a variety of anti-jamming measures, which can adapt to the distribution network voltage difference between nodes, thereby enhancing communication performance.

Introduction

With the development of various types of sensor technology and digital signal processing technology, the acquisition and processing of operating parameters are relatively mature [1]. Low cost, high reliability of the monitoring data communication system is the remote monitoring methods to promote the application of an important part and difficult.

To power lines for the media to transmit information, with a small investment, without laying communication lines, no service costs, flexibility and other advantages, by the widespread concern. The mechanism of Two Way Automatic Communication System (TWACS) [2] is to use the grid voltage and current waveform of small distortion to carry information, distortion signal frequency is less than 1000Hz, you can cross the transformer, so the technology can achieve direct communication across the transformer platform without the need for relay links, In order to reduce the modulation power, the signal modulation is carried out in the voltage zero crossing area. The detection mode of the frequency communication signal is related to the waveform characteristics of the modulation signal, the transmission attenuation, the channel noise and so on. Therefore, the research of the power frequency communication includes two aspects: modulation and demodulation of the signal and transmission characteristic analysis [3].

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In order to make the power line frequency communication technology can reliably transmit data, a new power line frequency communication technology research, including multi-feeder, three-phase, multi-channel signal transmission model research, multi-channel frequency signal modulation and demodulation technology research , Communication protocol research. On this basis, the development of multi-channel frequency communication system which adapts to the actual channel environment of distribution network in China, including various connection methods which can adapt to the user's transformer, and finally establish the demonstration of electricity consumption in remote area.

With the continuous development of energy Internet, the need to monitor and transfer the amount of data is growing, the frequency of communication frequency communication should also continue to improve to meet the growing demand for energy and development of the Internet. According to the characteristics of power frequency communication can learn the three-phase transmission technology, multi-channel, multi-feeder technology [6]. According to the energy Internet access equipment complexity, line noise and other characteristics, the need to study the corresponding interference suppression technology or other methods to enhance the reliability of communication. And according to the geographical scope of monitoring and management, select the appropriate power line communication, research to improve the communication performance of the key technologies, so that monitoring data through the power line real-time, reliable transmission, remote monitoring for the motor group to promote the application to create favourable conditions, Academic significance and engineering application value.

Related Work

United States Reed H. Johnston first proposed power line frequency communication ideas, the basic principle is the use of modulation voltage waveform to achieve information transmission, are simplex communication. In the 1980s, the United States Mak, ST [7] proposed TWACS the basic concept of voltage modulation with the previous simple mode, while the other way the information transmission through the current modulation , Thus realizing the two-way transmission of information. As the North American power grid channel interference is small, the technology has been in the remote meter reading, load control and other fields have been applied. In the 1990s, the United States experts proposed by orthogonal coding combined with the detection vector to achieve single-phase 6-signal uplink simultaneous interpretation method [8]. After 2000, North America in the field of research less, mainly concentrated in the frequency spectrum distortion signal spectrum analysis [9].

In the Frequency of Communication Signal Transmission Characteristics of the Study

Harbin Institute of Technology (HIT) based on the field measured signal, the modulation signal waveform is obtained by time domain difference method. The comparison between field test and transmission simulation shows that the transmission of power frequency communication signal in China is close to the model simulation [10]. Beijing Jiaotong University, Beijing 100083, China) the influence of the connection mode of distributed transformer on the transmission of power frequency modulation signal is studied. Among them, there is a phase difference between the one or two windings of the Dy11 transformer. There is amplitude attenuation when power frequency communication signals pass through this type of transformer[11]. North China Electric Power University proposed to meet the power quality standards under the premise of enhancing the amplitude of the modulation signal to improve the communication performance of the method [12].

In the Frequency of Communication Signal Detection Research.

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short Fourier transform is realized by adding the time window function to the signal after Fourier transform. Wavelet analysis is similar to short-time Fourier transform, but it has the advantage of automatically adapting to the time-frequency characteristic of the signal by stretching translation. Harbin Institute of Technology studied by the frequency analysis method, the basic feature is based on the frequency spectrum signal characteristics of the signal to the receiver voltage zero time as a benchmark. Compare the signal modulation area and the energy parameters of other areas to determine whether there is a modulation signal. Based on the phase difference of each node in the distribution network, the North China Electric Power University has studied the transmission delay problem of the power frequency communication signal. Based on the time-frequency analysis method combined with adaptive filtering and other anti-jamming technology, the adaptive frequency distribution method of adaptive distribution network node voltage difference is proposed.

The research on the transmission characteristics of power frequency communication signal at home and abroad shows that the attenuation of the distortion signal in the distribution network is not big due to the low signal frequency. However, due to the limitation of harmonic management and the cost of equipment, the modulation amplitude of the distorted signal is very weak, so the signal-to-noise ratio is very low when the frequency signal is demodulated. In the case of channel noise, the interference of the grid is more random, it is difficult to use accurate formula to express, the total situation is the existence of a large number of industrial distribution network non-integer harmonics, noise interference is much larger than the civil power grid. The study of the frequency communication channel is mainly focused on the signal through the transformer and its transmission attenuation in the power line. In the frequency of communication signal modulation and demodulation, the current focus is on the channel interference suppression method.

The Novel Frequency Communication System Structure

[image:3.612.155.456.481.667.2]

According to the distribution network structure and the power line frequency communication mechanism, through the multi-feeder, three-phase transmission, single-phase multiplexing proving the system's equivalent rate [1,4,7]. As shown in Figure 1, by the substation in the sub-station equipment and a number of low-voltage side of the distribution transformer terminal, the sub-station and the terminal through the voltage or current distortion signal to achieve information transmission.

Figure 1. New frequency communication system structure.

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Multi-Channel Parallel Signal Transmission Mechanism and Channel Model of Power Frequency Communication

[image:4.612.184.428.116.251.2]

The Mechanism of Frequency Communication

Figure. 2. Frequency communication system structure.

Power line frequency communication system shown in Figure 2, by the substation in the sub-station equipment and a number of low-voltage side of the distribution transformer in the terminal, the sub-station and the terminal through the voltage or current distortion signal to achieve information transmission. The signal from the slave station equipment to each communication terminal is called a downlink signal, which is usually the address code of the control instruction or the request information. The transmission device in the sub-station device generates a distortion signal in the vicinity of the voltage zero crossing by the modulation transformer, and the communication terminal passes Detection of voltage distortion signal to achieve downlink demodulation.

The signal from the communication terminal to the sub-station device is called an upstream signal, and the current signal is generated by the drive circuit in the terminal through the distribution transformer in the vicinity of the voltage zero crossing [3,11]. The upstream demodulation device in the master station is detected by the sensor, 10kV line current distortion signal to achieve uplink demodulation. Distortion signal is in the modulation terminal voltage near zero, A, B, C phase between the phase difference of 120 degrees, so that the modulation signal will not overlap each other, through A, B, C three simultaneous transmission frequency distortion signal, Can get 3 times the communication rate.

Multi-channel Transmission Scheme Design

Through the feeder, three-phase transmission, single-phase multiplexing, etc. can be multi-channel power signal transmission, thereby improving the system's equivalent rate [6,13].

The distortion signal is in the vicinity of the zero voltage of the modulation terminal, the phase difference between the three phases of A, B and C is 120 degrees, and the main component of the distortion signal exists for about 3 milliseconds, so that the modulation signal does not overlap with each other. Through A, B, C three-phase transmission frequency signal distortion at the same time, can get 3 times the communication rate. Single-phase multiplexing is for the uplink communication, the uplink signal using the distortion current representative. As the current harmonics is rich, each uplink data is expressed by four consecutive periodic waveforms. Four adjacent cycles have eight voltage zero crossings, which are carried out according to the principle of 2 positive 2 negative current distortion in four frequency cycles Data modulation [8].

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Multi-Channel Power Frequency Communication Signal Transmission Model

[image:5.612.143.471.192.262.2]

As a result of multi-phase, multi-channel parallel transmission, according to the distribution network structure to establish a comprehensive reflection of the frequency of communication signal transmission characteristics of the model. Power frequency signal transmission model will power lines, transformers, and load are equivalent to resistance and reactance, as shown in Figure 3.The transmission model is established for the power frequency communication signal transmission characteristic analysis, which is to realize the multi-channel signal parallel demodulation foundation.

Figure 3. Multi-channel frequency communication transmission model.

In the past, the frequency domain communication channel analysis is based on the local voltage zero crossing of the transmitter and receiver, and analyzes the amplitude attenuation and the waveform change of the power frequency communication signal through the transformer and the power line. In the distribution network, due to load, line impedance, transformer model and other factors, the voltage of each node there is zero time difference. Through the simulation analysis and field test, it is shown that the transmission delay of the modulation signal is much smaller than the zero crossing time of the voltage, and the demodulation time domain deviation occurs to reduce the communication performance. This effect cannot be solved fundamentally by means of signal filtering and interference suppression.

Study on Transmission Characteristics of Power Frequency Communication Signals

Power frequency modulation signal in the transmission side of the voltage near zero, and signal detection can only take the terminal voltage zero for reference. In order to improve the detection performance, it is necessary to analyze the waveform of the modulation and reception side of the modulation signal and the system voltage waveform at the transmitting and receiving side so as to obtain sufficient power frequency modulation signal information at the time of signal reception.

The upper and lower signal modulation and transmission models shown in Fig. 4 are established by taking the user terminal 1 and the 10KV branch k in Fig 3.In Figure 4, F and G are the Frequency communication master station and terminal equipment location. w is the frequency of the power frequency. at the main station, R1+jwl1 for the substation main transformer equivalent impedance, R+jwl for the modulation transformer and modulation device including the equivalent impedance, R2+jwl2 for the transmission line equivalent impedance, R3+jwl3 for the transmission line The equivalent impedance of the corresponding load at the end.

In the G position of the communication terminal, R3+jwl3 for the distribution transformer equivalent impedance,R5+jwl5 for the transformer power supply within the range of the equivalent load impedance, R’+jwl’ for the uplink signal modulation impedance.

[image:5.612.194.422.644.726.2]
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The control switches Sand S' are implemented with thyristor. When S is closed at 30° before the local voltage is zero (t=t0), the downstream voltage distortion is generated when the voltage is close to zero (t=t1) Similarly, the on-off of the switch S' can produce current distortion iG.

The upper and lower power frequency modulation signals are carried out before the transmission voltage is zero, and the signal demodulation is carried out at the receiving end. Therefore, there is a need for signal transceiver terminal voltage phase difference, and the frequency of communication signals in the distribution network in the transmission delay.

In the distribution network, the voltage difference between the vertical and horizontal changes of the voltage between the nodes can be reflected. Let U1and U2 for the transceiver node voltage.P2and Q2are the line between the active and reactive power, R +jX is line impedance.

The vertical variation of the line voltage is:

2 2 2 U X Q P

U = +

(1)

The voltage transitions are:

2 2 2 U R Q X P

U = −

δ

(2)

The voltage difference between nodes is:

U

U

U

tg

+

=

− 2 1

δ

δ

(3)

Signal transceiver between the 10KV line length reach about 20 km, according to the parameters of the reference, the line impedance is:

km

km

j

km

jX

R

+

=

(

0

.

48

/

+

0

.

34

/

)

×

20

(4)

Sis the apparent power (unit: MVA) and ϕ is the power factor. According to equations (1) to (3), the absolute value of the voltage difference between nodes (unit: degrees) is shown in Table 1 for different power and power factors.

In the actual distribution network, the impedance of different lines vary greatly. Reference to the relevant literature parameters, line impedance is:

km

km

j

km

jX

R

+

=

(

2

.

18

/

+

1

.

33

/

)

×

20

(5)

When this line parameter is included, the voltage difference between nodes is shown in Table 2 under different apparent power (unit MVA) and power factor.

[image:6.612.101.511.610.729.2]

As can be seen from Table 1 and Table 2, the lower the power factor, the greater the difference in voltage between nodes.

Table 1. Voltage phase difference in the distribution network (absolute value).

S/MVA cos

1 1.2 1.4 1.6 1.8 2

0.3 3.7 4.3 5.03 5.6 6.2 6.8

0.4 3.1 3.7 4.2 4.7 5.2 5.7

0.5 2.5 2.9 3.4 3.8 4.2 4.6

0.6 1.8 2.1 2.4 2.7 3.0 3.3

0.7 1.0 1.2 1.4 1.6 1.7 1.9

0.8 0.16 0.19 0.2 0.2 0.2 0.3

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[image:7.612.95.517.83.202.2]

Table 2. Voltage phase difference in the distribution network (absolute value).

S/MVA cos

1 1.2 1.4 1.6 1.8 2

0.3 13.7 15.5 17.1 18.5 19.8 21.0 0.4 11.7 13.2 14.6 15.8 16.9 17.8 0.5 9.6 10.9 12.0 13.0 13.8 14.6

0.6 7.4 8.3 9.2 9.9 10.6 11.2

0.7 4.9 5.5 6.0 6.5 6.9 7.3

0.8 1.9 2.2 2.4 2.6 2.8 3.0

0.9 1.7 1.9 2.1 2.3 2.4 2.6

Conclusion

Power line frequency communication technology uses the grid voltage and current waveform of small distortion to carry information. It can cross the transformer remote communication, suitable for distribution network line structure and load characteristics. It has the advantages of low cost of equipment, easy installation, no communication service costs and so on. But the power line frequency communication there is a low rate of defects, and the traditional modulation and demodulation are based on the local voltage zero, because the transceiver system voltage phase difference caused by receiving time domain deviation, which seriously affect the communication performance. In this paper, the paper establishes a multi-channel signal transmission model based on the technical mechanism of frequency communication, and improves the communication rate by means of single-phase multiplexing, three-phase transmission and multi-feeder parallel transmission. At the same time, based on time-frequency analysis to determine the frequency domain communication signal modulation time domain, combined with a variety of anti-jamming measures, which can adapt to the distribution network voltage difference between nodes, thereby enhancing communication performance.

Acknowledgment

This paper is partially supported by the key projects in Tianjin science & technology pillar program under the grant 17YFZCGX00610 and the Science and Technology Research Foundation of Tianjin Electric Power Company under the grant KJ16-1-04, KJ17-1-23 and KJ17-1-49.

References

[1]Zheng Feng Ming,Guang Zheng Ni, Bing Zhong Yang. Performance Analysis of Three-phase Capacitor Motor in Frequency Control System [C]. 2010 Twenty Fifth Annual IEEE Applied Power Electronics Conference and Exposition, 2010:109-111.

[2]Douglass P J, Kai H, Shi Y, et al. System Frequency as Information Carrier in AC Power Systems[J]. IEEE Transactions on Power Delivery, 2015, 30(2):773-782.

[3]Vasu C L, Jayaparvathy R. Automatic meter reading using power line signaling and voltage zero-crossing detection[J]. Research Journal of Applied Sciences Engineering & Technology, 2015, 10(4):414-424.

[4]Ramanathan K, Muniraj N J R. DWT-IDWT-based MB-OFDM UWB with digital down converter and digital up converter for power line communication in the frequency band of 50 to 578 MHz[J]. Annals of telecommunications—annales des télécommunications, 2015, 70(5-6):181-196.

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[6]Facina M S P, Ribeiro M V. The influence of transmission power and frequency bandwidth on in-home cooperative power line communication[C]// International Symposium on Power Line Communications and ITS Applications. IEEE, 2015:239-244.

[7]Mak S T, Moore T G. TWACS™, a New Viable Two-Way Automatic Communication System for Distribution Networks. Part II: Inbound Communication[J]. Power Engineering Review IEEE, 1982, PAS-101(8):2941-2949.

[8]Wulich D, Goldfeld L. Reduction of peak factor in orthogonal multicarrier modulation by amplitude limiting and coding[J]. IEEE Transactions on Communications, 1999, 47(1):18-21.

[9]Soong F, Sondhi M M. A frequency-weighted Itakura spectral distortion measure and its application to speech recognition in noise[C]//Acoustics, Speech, and Signal Processing, IEEE International Conference on ICASSP. IEEE, 1988:625-628.

[10]Zhang Shiping, Zhang Shaoqing, Liu Ruiye. Two-way power frequency automatic communication system (TWACS) signal transmission characteristic analysis on power distribution network[J]. Power System technology, 2003, 27(5):63-66.

[11]Yan Suyun, Wang Yi. Analysis of Signal Transmission in TWACS[J]. Journal of Beijing Jiaotong University, 2005, 29(5):103-106.

[12]Lu Wenbing, Luo Yingli, Yan Ying, et al. Transfer Characteristic Simulation and Field Application Research on Two Way Power Frequency Automatic Communication System Signals[J]. Power System Technology, 2011(4):187-193.

Figure

Figure 1. New frequency communication system structure.
Figure. 2. Frequency communication system structure.
Figure 3. Multi-channel frequency communication transmission model.
Table 1. Voltage phase difference in the distribution network (absolute value).
+2

References

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