Information acquisition technology for small hydropower stations in remote areas based on high- and low-orbit satellites

0 Introduction

With the development of a strong and smart grid,new services such as advanced distribution network monitoring,distributed power access,and smart power interaction are constantly emerging.New services require communication networks with extensive and flexible edge access capabilities at the access layer.However,the increasing access of distributed power sources(DG),the increasing penetration rate of electric vehicles,and the increase in controllable loads challenge traditional distribution networks[1].Electrical automation mainly uses optical fiber communication in the “three remote” communication nodes;the intelligence of distribution network automation and the coverage area must be improved.The electricity consumption information collection system uses power line carrier technology for communication that is technically inferior.The communication bandwidth and performance are insufficient for satisfying the requirements of smart electricity.The low-voltage centralized copy system generally meets the 95% success rate requirement for daily inspections.

The Satellite data acquisition system(DCS)can automatically extract and send collected data.The data rate is low and the data is collected in time-sharing.The coverage area is wide and not restricted by the environment or geographical conditions.It can work in the field without manual supervision,and is suitable for installation in harsh environments.The DCS is used worldwide in environmental,marine,and meteorological monitoring,offshore oil and gas platform monitoring,and small hydropower station information collection in remote areas.DCS satellite communication provides good antiinterference performance,low power consumption[2-6],and a large transmission capacity.A network can be easily constructed for information collection from small hydropower stations in remote areas,providing solutions for the multi-business needs of the power grid.

1 Information collection technology requirements for small hydropower stations in remote areas

1.1 Current small hydropower information collection technology

At present,primarily three methods are used for collecting information from small hydropower plants:optical fiber communication,4G communication,and manual collection.

For small hydropower stations that are close to the substation,the cost of optical fiber communication access is not high;a few small hydropower stations use optical fiber communication.At small hydropower stations facing high costs for optical fiber access in 4G service areas,meter data is collected and sent in 4G mode.The power grid still contains many small hydropower stations in remote areas that are not connected to dispatching and electric energy collection systems.Data collection from these stations has increased labor costs and the difficulty of controlling the power grid load,which has reduced the capability for power grid management.

Using high- and low-orbit satellites to communicate in remote areas can compensate for a lack of communication infrastructure,and effectively improve the management and control risks caused by a large number of small hydropower stations that are not connected to dispatch and electric energy acquisition systems,effectively improving the quality and efficiency of information collection[5].

A high- and low-orbit satellite hybrid data acquisition system has unique advantages including advanced network architecture,stability,reliability,safety,and efficiency.In conjunction with the electricity consumption information acquisition system,it can provide convenience in the daily work of the power grid.The system is of special significance in the construction of electricity information collection systems in areas outside public network signal coverage in the Guangdong Power Grid and the Southern Power Grid,such as small hydropower stations in remote areas.In the realization of an automated measurement information collection system,the goal of “full coverage,full collection,and full monitoring” is advancing,providing a solid foundation for construction of an intelligent power grid.

1.2 System function requirements

In terms of effectiveness and safety,satellite communication systems for small hydropower information collection services in remote areas must meet the following functional requirements:

(1)Provide satellite communication for multi-business and grid-connected monitoring;

(2)Provide reliable communication for information collection;

(3)Provide multi-band antenna signal reception from DCS satellite terminals;

Satellite communication systems offer high security and low power consumption.The test platform must perform these functions,consider satellite network control,and not affect normal operation of the main power station.A set of main station power distribution systems simulating satellite access must be constructed,with laboratory verification[6-7].

DCS satellite communication can cover a wide area and is not restricted by environmental or geographical conditions.It delivers satisfactory anti-interference performance and achieves low power consumption.It can function in the field without manual supervision and is suitable for installation in adverse environments.It has a large transmission capacity,and networks can be easily constructed;this allows for synchronous multi-region remote sensing and providing solutions for the multi-service requirements of the power grid.

The DCS has hundreds to tens of thousands of data collection platforms,with a wide distribution range including remote land and sea areas.The data collection platforms are scattered and mutually exclusive.The distances between them differ;they can be tens to hundreds of kilometers apart[8].Data can be uploaded in a few seconds to meet the requirements of businesses handling large amounts of data.

2 Overall design

The information acquisition system for small hydropower stations in remote areas using high- and low-orbit satellites uses the B-S structure.The master station uses an SQL database+WEB browsing method for management.The terminal uses a communication interface board consisting of a communication module,a power supply module,and a storage module.The communication module has a debugging interface,an electric meter communication interface,a satellite communication interface,and an RS485/RS232 reserved port.The storage module includes a flash memory module and EPROM memory[9-13].EPROM memory saves the basic information of the device;the flash memory module is used as a backup.The communication interface board regularly collects electricity meter data,checks and analyzes received electricity meter messages,and sends them to the satellite at regular intervals,as shown in Fig.1.

Fig.1 Overall system structure

2.1 Hardware design of terminal equipment

2.1.1 Satellite communication module

This project uses a satellite communication digital demodulation and broadband modulation module[14-17].This module is used mainly in satellite communications,including forward demodulation and backward modulation.Forward remote control demodulation captures,tracks,decodes forward signals,and outputs demodulated data.Backward modulation frames,encodes,and modulates the payload data,and outputs the L-band intermediate frequency signal.

Fig.2 shows the modem signal processing flowchart.

Fig.2 Modem signal processing flowchart

The main parameters of the satellite communication module are:

(1)Implementation method:FPGA + peripheral circuit;

(2)Intermediate frequency:receiving and transmitting L frequency band;

(3)Information rate:data rate from 48 kbps to 10 Mbps

(4)Modulation method:BPSK(spread spectrum),QPSK,8PSK;

(5)Working mode:Four modes.

The receiving and transmitting rates,spreading codes,code clocks,and modulation modes corresponding to the four working modes can be configured arbitrarily;four software programs are dynamically loaded,and the related software module parameters are set.

2.1.2 Satellite modem terminal

The satellite modem terminal consists of a core board and a control board;the core board and control board each consist of two stacked boards.The satellite modem terminal is shown in Fig.3.

Fig.3 Modem terminal

2.2 Design of DCS satellite data acquisition background software

The background software consists of equipment modules,operating modules,maintenance modules,and security modules.The equipment module is responsible for the access control of the satellite commander and the access control of the main station platform;the operation module is responsible for the mutual conversion,data transmission,and reception between the satellite protocol and the power protocol;the maintenance module is responsible for monitoring and maintenance of communication failures;the security module provides security protection mechanisms.

3 Security protection of DCS satellite communication system

Considering the new business and network threats faced by DCS satellite communications in the distribution network,secure access and channel monitoring technology was developed for power distribution services and equipment,and a security monitoring device was designed.Fig.4 shows the overall DCS satellite communication architecture in power communication channel monitoring,which includes a master station,a terminal,and a communication network.The secure access gateway provides end-to-end security protection for data interaction between the master station and the terminal through identity authentication,data encryption,data decryption,and data signature;this ensures the integrity and security of the data between the master station and the terminal[18-20]for anti-leakage,anti-tampering,and anti-replay protection,thus preventing takeovers and other malicious attacks.

Fig.4 Overall architecture of DCS satellite power communication channel monitoring

3.1 Network anomaly detection based on support vector machine

The binary classification support vector machine algorithm is a classification algorithm based on the space interval feature.The learning strategy of the support vector machine involves maximizing the interval.As the objective function is a quadratic function,it can be formalized as convex quadratic programming,which is equivalent to the minimum of the regularized hinge loss function.Assuming a linearly separable training data set on a feature space,

where ξ is a slack variable that allows a certain parallel movement of the classification decision plane,such that it can resist sample noise;ρ is the minimum distance between the classification plane and the sample.When ρ = 0,the classification plane is on the straight line determined by the support vector,and v is the penalty coefficient.

For network attacks and network abnormalities such as unbalanced or non-negative data[21],one-class support vector machines can be used for algorithm training.

3.2 Simulation analysis of network anomaly detection based on support vector machine

Group 1 data_1_list is used to minimize Eq.(6).To reflect the role of the slack variable ξ,all ξ terms in Eq.10 are removed to obtain the following results:Samples 3,9,and 10 are support vectors;the three lines are the separating hyperplanes corresponding to the three support vectors.The blue solid line represents the maximum value,which is the target hyperplane[20].

The distance from the origin is .

Fig.5 shows the separated hyperplane of group 1 data after training.

Fig.5 ing

The separating hyperplane is on the support vector;the relaxation variable ξ is introduced[23]and is minimized by data_1_list in Eq.(6)to obtain the following results:

Fig.6 Separated hyperplane of group 1 data with relaxation variable added

In Fig.6,the red line is the new decision-making hyperplane,separated from the blue line by a certain distance to accommodate sample noise.

4 Information collection and testing of small hydropower plants in remote areas

The data acquisition system architecture designed in this study using a hybrid of high- and low-orbit satellites consists of a satellite data collection master station system,high/low orbit satellite terminals,and several high- and low- orbit satellites.

High-orbit satellites provide wide single-satellite coverage and a long overhead duration.Only a few satellites are required for continuous coverage and data communication[24-27].With a high satellite orbit,the terminal must have high transmission power and high receiving sensitivity;nonetheless,the data transmission delay is relatively high.The receiving frequency band of the high-orbit satellite is 12.25-12.75 GHz;the transmitting frequency band is 14.00-14.50 GHz;the data transmission rate is 64 kbps-3.88 Mbps;the maximum output power of the power amplifier is 8W;the modulation methods are BPSK,QPSK,and 8PSK;and the encoding method is LDPC+BCH,using Zhongtong series satellite resources compatible with existing satellite resources.

Low-orbit satellites work in the 300 MHz frequency band and provide communication rates from 200 bps-3.2 kbps[28-30].The Apocalypse constellation uses Guodian Hi-Tech satellite series resources and consists of 38 loworbit,low-inclination small satellites,of which 36 have an orbital height of 900 km and an orbital inclination of 45°.There are six satellites on each orbital plane,and a total of six orbital planes;there are also two sun-synchronous orbiting satellites.Low-orbit satellites are configured in loworbit constellations.They are easy to launch,with a short transmission delay,low path loss,and correspondingly low transmission power[31-32];the single-satellite coverage area is small,with a short duration.A complete constellation(dozens of satellites)is necessary for comprehensive coverage and uninterrupted data transmission.

(1)Test environment

Suitable pilot small hydropower stations in remote areas were selected for collection of electricity consumption information.The satellite data collection terminal can perform functions such as remote meter reading,billing,electricity consumption inspection,and share electricity consumption information with the power supply department.Collection of electricity consumption information using a satellite data collection terminal was verified.

(2)Test results

The satellite data collection terminal can synchronously read and receive data,such as the current total active energy,current,voltage,and current time of the meter,and can detect communication failure with the meter communication terminal.

Data collection using secondary equipment must conform to DL/T698.45,IEC101/104,IEC61850,and other protocols;

The satellite data collection terminal can synchronously copy and collect object-oriented data defined by secondary equipment and can detect communication failure between the collection unit(data transmission terminal)and secondary equipment terminals.The communication function includes satellite data transmission terminal management,satellite communication channel resource management and performance detection,and communication transmission.

In testing and collecting electricity meter information,the communication interface board obtains the number of electricity meters through the 485 interface.The electricity meter information is collected regularly(total active energy,total reactive energy,voltage,current,etc.,collected every 15 min).The satellite communication board has limited time online;data is sent regularly to the satellite communication board.

After the power is connected,the green power light is illuminated.Failures include:the satellite communication board does not indicate data transmission status,hardware detection fails,and illumination of the red warning light.The communication interface board MCU enters the working mode,and the blue light is illuminated.Table 1 shows the data collected from small hydropower stations.

Table 1 Information collection from small hydropower stations in remote areas

Small hydropower station Instantaneous power/kW Instantaneous no power/kVArh Active energy/kW Reactive energy/kVArh 071706180180.681980.1329.09317.61 071706180278.738378.1229.09317.58 07170618030.00120.00189.08917.54

5 Conclusion

With a wide coverage area and little influence from geographical factors,satellites can serve the needs of remote areas with “full coverage” communication.This study investigated a satellite data transmission system.The information collection needs of small hydropower stations in remote areas were analyzed,and an information collection system was designed using high- and low-orbit satellites.In response to the increasing frequency of network attacks,a network anomaly detection method based on a support vector machine algorithm was designed.An information collection test was conducted;the test results showed that information collection from small hydropower stations in remote areas was realized using the high- and low-track hybrid data transmission system.

Acknowledgement

This work was funded by the Guangdong Power Grid Co.,Ltd.Technology Project(GDKJXM20180019).