Research on Cascading Scheme of Electric Energy Information Collection Terminal

1 Introduction

The power information collection and management system is a hot topic in the research and construction of power companies all over the country in recent years. The power information collection terminal is an important part of the power information collection and management system, and it is also the most numerous device in the power information acquisition and management system. It is responsible for the collection of energy information at various information collection points, data management, data transmission, and execution or relay of control commands issued by the master station. According to the application occasions, the power information collection terminal can be divided into a plant station collection terminal, a dedicated variable collection terminal, a public variable collection terminal, and a low-voltage centralized meter reading terminal (including a low-pressure concentrator and a low-pressure collector). The channel used for communication between these different types of energy information collection terminals and the master station is somewhat different. Because the station station collection terminal is mainly installed in the substation or substation, the communication conditions are good, and the upstream communication channel mainly uses the network. , Special line or telephone dialing, special collection terminal and public variable collection terminal due to more decentralized, uplink communication channel mainly uses GPRS/CDMA, 230M radio station, etc. Low-voltage centralized meter reading terminal takes into account the cost factor, and the upstream communication channel mainly uses telephone dialing. GPRS/CDMA, etc. It can be seen that many of the communication between the energy information collection terminal and the master station are based on communication channels provided by third parties, such as GPRS/CDMA, telephone dialing, and the like. Utilizing the communication channel provided by a third party, the power company can eliminate the operation and maintenance of the communication channel and reduce the staffing of the operation and maintenance personnel. At the same time, the quality of the communication channel can be ensured. Therefore, in actual use, the collection terminal of the above-mentioned demolition plant station has an existing one. The ratio of the third-party communication channel for the exclusive use of the power dedicated channel to the other three types of terminals is quite high, and local power companies have reached a certain consensus on this: In addition to special requirements for security, the use of third-party communication channels is currently Better choice.

Using a third-party communication channel, the power company needs to pay communication companies monthly for communication costs. At present, power companies use packages to form communication tariff agreements with communication companies. Packages are charged separately for each terminal, so the number of terminals increases. The corresponding increase in tariffs. Some practical applications in the field need to install multiple terminals. If multiple terminals share an uplink communication channel to communicate with the master station, the communication cost will be greatly reduced. At the same time, only one terminal needs to configure the communication module, and the other terminals do not need any more. By configuring the communication module, the cost of purchasing the terminal is also greatly reduced, and the power consumption of the unconfigured communication module terminal is reduced, so the reliability is also strengthened. The cascading scheme is proposed to implement multiple terminals sharing an uplink communication channel.

2 Functional Requirements Analysis

Cascading is the way that terminals are connected through the local interface between each other and use the remote channel of one of the terminals to communicate with the master station. The terminals participating in the cascade may be the same type of terminal, or may be different types of terminals (there are many low-frequency concentrators and public variable collectors cascaded at the site). The research of the cascading scheme should be to minimize the participation level. The impact of the terminal's capabilities and performance is targeted.

(1) Real-time

The command sent by the master station to the slave terminal should have the highest priority. Here, the commands sent from the terminal include real-time call measurement of the power data of the terminal itself or an external power meter, setting parameters, remote pull-out, and the like. When receiving the commands, the master terminal preferentially forwards the commands to the slave terminals when determining that the local bus is free. At the same time, the master terminal of the response frame from the terminal should also forward to the master station with priority when judging that the uplink communication channel is idle, thereby ensuring the requirement of real-time response to the master station command.

(2) Timeliness

Except when the master station sends a command to the slave terminal, the system normally operates normally when the system runs normally. The active reporting data mainly includes two types of scheduled task data and abnormal alarms. Among them, the timing task data includes various kinds of electric energy data, instantaneous quantity data, etc., which are regularly sent to the master station according to a set time interval (for example, every 15 minutes); abnormal alarms occur from time to time and require the terminal to be at the most The master station was informed of the anomaly that occurred on site at a time. Since the slave terminal itself does not have a remote communication channel, it is unrealistic to report these data to the master station in real time. However, there is a timeliness requirement in designing the concatenation scheme. Usually, the report forwarding can be completed within 5 minutes. Application requirements for timeliness.

(3) Low-voltage concentrator reads the power of the collection terminal

Because the public variable collection terminal has the function of energy metering in design, its energy metering error level is completely in accordance with the requirements of the first-class multi-function electric energy meter. Therefore, although they cannot be used for settlement and billing, it is entirely possible to use line loss assessment. Therefore, if a common transformer is installed on a utility transformer, it is no longer necessary to install an assessment meter. In addition to achieving its own function, the public transformer collection terminal also undertakes the task of evaluating the bus. On the other hand, the low-pressure concentrator is designed to calculate the line loss rate, thereby reducing the pressure on the master station, and sending an alarm to the master station actively when the online loss rate exceeds the standard. In order to calculate the line loss rate, the low-pressure concentrator needs to read the electricity data of the public variable collection terminal. Therefore, the design cascading scheme should properly handle the operation flow of sharing the two major functions of the long-distance communication channel and the reading of the data of the public variable collection terminal.

3 Cascade solutions

3.1 Principle wiring

The terminals participating in the cascade use the 485 bus as the cascading local interface. The terminal with the remote upload channel is the main terminal. The terminal that uses the remote upload channel of the main terminal to communicate with the main station is the slave terminal, and the slave terminal does not have the remote upload. Channel, or remote upload channel is not enabled. The master terminal and the slave terminal may be any of a special collection terminal, a public variable collection terminal or a low-voltage concentrator. Considering the practical application of the site and the communication pressure of the master terminal, it is appropriate that one master terminal is designed to cascade up to four slave terminals. The principle of the cascade scheme is shown in Figure 1.

Figure 1 Schematic diagram of the cascade scheme

3.2 Shared Remote Channel Scheme

When the destination address of the request command frame initiated by the master station is the slave terminal, the master terminal judges that the destination address is not the master terminal itself after receiving the command, and forwards the command to the cascaded 485 bus immediately. There should be 4 slave logical addresses under the main terminal setting parameters.

The master terminal has the initiative to report functions, while the slave terminal does not have a remote uplink channel, so the active reporting function is limited. The initiative reporting function of the terminal is implemented in the following manner: When the communication terminal is idle, the master terminal actively initiates a query request to the cascading slave terminals every 5 minutes. The response is given from the terminal and the reply command is returned. After receiving the normal response frame from the terminal, the master terminal immediately establishes cascade communication, waits for receiving the report data of the slave terminal, and immediately forwards the data to the master station through the remote uplink channel. After the first transmission of data is completed, a cascade transmission control command is issued to notify the slave terminal to continue transmitting the subsequent data.

The low-voltage concentrators and public variable collection terminals in the same cascade system can exchange the total power data of the station area through specially defined instructions for the low-voltage concentrator to perform line loss analysis. The master terminal in the cascaded system should be able to recognize such a read command and perform the necessary forwarding work to assist in completing the information exchange from the terminal.

In order to achieve the above principle, the following commands are needed:

(1) Master terminal polling (control code C=18H) and slave terminal answering command (control code C=98H): The slave terminal response command frame should have a flag to indicate whether there is data to be uploaded from the terminal, so that the master terminal Know which cascaded data communication to establish a shared remote channel with the terminal.

(2) Cascade transmission control command (control code C=28H): When cascading transmission is used to communicate with the master station from the terminal, once the master terminal and the slave terminal establish cascade communication, the data reported from the terminal must be controlled , otherwise the master's slow upstream (eg GPRS/CDMA) channel will block. The master terminal receives the report data from the terminal and forwards the master station through the upstream channel as soon as possible. After the completion of the transmission, the slave terminal sends a cascade transmission control command to notify the slave terminal. After receiving the frame, the master terminal allows the subsequent frame to be reported.

3.3 Low-voltage concentrator reads the day-end frozen power plan of the public variable collection terminal

In order to calculate the line loss, the low-pressure concentrator needs to read the daily frozen electricity amount from the corresponding public variable collection terminal. According to the different positions of the low-voltage concentrator and the corresponding public variable acquisition terminal in the cascade system, the operation flow is different:

(1) The low voltage concentrator is the main terminal, and the corresponding change acquisition terminal is a slave terminal.

The low-voltage concentrator sends a data request command (control code C=17H) through the cascade channel, and reads the daily frozen power from the corresponding public acquisition terminal. The public variable acquisition terminal directly includes the daily frozen power data in the response frame (control code C). =97H) returns to the low pressure concentrator. Both the request frame and the response frame shall contain both the low-voltage concentrator and the public variable collection terminal address.

(2) The low-voltage concentrator is a slave terminal, and the corresponding mechanized acquisition terminal is the master terminal.

The low-voltage concentrator waits for a cascade transfer control instruction (control code C=18H or 28H) of the public variable acquisition terminal. After receiving the cascade transmission control instruction, the low-pressure concentrator sends a data request instruction (control code C=17H) to the public variable collection terminal through the cascade channel, and requests to read the daily frozen power from the corresponding public variable collection terminal. The public variable collection terminal directly sends the daily frozen electricity data to the low-voltage and low-pressure concentrator in the response frame (control code C=97H).

(3) The low voltage concentrator and the corresponding public variable acquisition terminal are not the main terminal

The low-voltage concentrator waits for a cascade transfer control command from the master terminal (control code C=28H). After receiving the cascade transmission control instruction, the low-pressure concentrator sends a data request instruction (control code C=17H) to the public variable collection terminal through the cascade channel, and requests to read the daily frozen power from the corresponding public variable collection terminal. The public variable collection terminal directly sends the daily frozen electricity data to the low-voltage and low-pressure concentrator in the response frame (control code C=97H) (at the same time, the main terminal also received the data request command). The low-pressure concentrator receives the response data, saves the data, and exits the cascading polling flow. At the same time, the master terminal also receives the data request command. After the master terminal recognizes the data request command, it considers the low-pressure concentrator. The control of the cascaded 485 bus has been returned and preparations are being made to poll the next slave terminal or to forward the master station). Detailed flow chart shown in Figure 2.


The flow chart is as follows:

(1) After the master terminal sends a transmission control command to send a control code C=28H to notify the low-pressure concentrator to start taking a table, there should be an overtime judgment mechanism. The timeout period is set to 5 seconds by default. At this time, if there is a command from the master station to the slave terminal to the master terminal, the master terminal should wait for the timeout before forwarding the command.


Figure 2 Flow chart of the cascade solution (the low-voltage concentrator and the corresponding common-acquisition acquisition terminal are not the master terminal)

(2) In the flow from the low-voltage concentrator and its corresponding mechanized acquisition terminal, the master terminal can receive all commands and data frames in real time through the cascaded 485 bus. At this time, the master terminal should serve as a monitoring device and monitor the slave terminal. 485 bus usage. Whenever a correct frame is received, the timeout counter is cleared and the timeout is recalculated; after the public variable acquisition terminal answers the low-voltage concentrator, it is assumed that the low-voltage concentrator has returned control of the 485 bus, and the pair should start to The next polling job from the terminal.

(3) The content of the flow chart rectangle box is a cyclic execution process. Only when the low-pressure concentrator reports all the data or does not report the data, it will send a 17H command after receiving the 28H control command. The table.

(4) If the low-pressure concentrator does not receive the 97H response frame, it should wait for the next poll to issue the meter reading command again, which is equivalent to copying (can only be performed within the same day, because the energy data field in the returned frame Only the day's date data).

4 Summary

The power information acquisition terminal realizes the sharing of the remote communication channel through the cascade, and has very important practical value in the construction of the power information acquisition and management system. However, since cascading is often involved in a variety of situations in the field, the terminals involved in the cascading may not be the products of the same manufacturer, or may not be the same type of products, and the cascading itself has a certain degree of complexity. It is difficult to apply the cascading function to the site. For this purpose, a set of test software for the cascading function is required to be developed. Consistent automatic tests are performed on various terminals with cascading. Only terminals that pass the consistency test can be cascaded with each other. Only in this way can the terminal be avoided. This will lead to side effects, and only in this way can the cascade function be truly used in the construction of the power information acquisition and management system.