Power supply voltage monitoring system based on ZigBee wireless network

Traditional power monitoring systems mostly use wired connections. When there are many monitoring nodes, there are problems such as difficult installation, cumbersome wiring and inconvenient maintenance. Using a wireless sensor network based on ZigBee technology to build such a power monitoring system can solve the above problems. This article introduces the working principle of ZigBee technology and the design of a real-time monitoring system.

The ZigBee protocol stack structure consists of the physical layer, MAC layer, network layer and application layer. The ZigBee standard stipulates that all ZigBee network nodes are divided into three types: Coordinator, Route, and End Device. Regardless of the topology adopted by the ZigBee network, the network will automatically select a better routing path as a data transmission channel according to the ZigBee protocol algorithm to improve communication efficiency.

1 Monitoring system design

1.1 System structure design

The block diagram of the power supply voltage monitoring system based on ZigBee wireless network is shown in Figure 1.

Figure 1 System structure frame

The terminal node collects the 0~30 V voltage data of the power supply equipment through the acquisition/protection module, and sends it to the coordinator node through the router node. At the same time, it also receives the control command of the coordinator and processes it accordingly; the main task of the router node in the system is data transfer, ensuring the correct data exchange between the coordinator node and the terminal node, and increasing the coverage of the ZigBee network; on the one hand, the coordinator node receives the power supply voltage data collected by the terminal node and sends the data to the host computer through the serial port, and on the other hand, receives the command information from the host computer and then sends it to the corresponding terminal node; the host computer manages the status information of the monitoring equipment, including system configuration, real-time status display, node control, data processing and data query, etc.

1.2 Network topology selection

ZigBee network has three topological forms: star topology, tree topology, and mesh topology. The monitoring system designed in this paper chooses mesh topology as the system topology.

2 Hardware Design of ZigBee Monitoring System

The monitoring system is mainly composed of router nodes and terminal nodes.

The hardware structure diagram of the terminal node is shown in Figure 2.

The terminal node module consists of two parts: acquisition and control. The power supply adopts DH1718G-4 DC regulated power supply. The power supply voltage 0~30 V is converted into 0~3 V voltage for CC2430 on-chip AD acquisition using 1/10 resistor divider; the protection module includes two parts: relay and buzzer circuit. The relay is used to cut off or restore the connection between the power supply and the load device, which plays the role of overvoltage protection. The buzzer sounds when the power supply is overvoltage, which acts as an alarm. Among them, a diode is added to the relay drive circuit to release the large reverse electromotive force generated by the relay coil at the moment of power failure of the relay, which plays the role of protecting the transistor.

Figure 2 Hardware structure of the terminal node

3 Software Design of ZigBee Monitoring System

3.1 Z-Stack Software Architecture and Customization

The software development platform of ZigBee wireless network node adopts IAR Embedded Workbench V7.30B for 8051 (IAR EW) integrated development environment. The software system protocol stack of ZigBee wireless module is constructed with the idea of ​​operating system and adopts "event polling" mechanism. After each layer is initialized, the system enters low power mode. When an event occurs, wake up the system, start interrupt processing event, and continue to enter low power mode after the end. If several events occur at the same time, judge the priority and process the events one by one. The main workflow of the whole Z-Stack is roughly divided into: system startup, driver initialization, OSAL initialization and startup, and enter event polling stage.

3.2 Software Design of Coordinator Node

The role of the coordinator in the system is to establish and manage the ZigBee network, automatically allow other nodes to join the network, collect voltage data from the terminal nodes, and send the data to the host computer through the serial port. At the same time, it receives control commands from the host computer and sends the commands to the terminal nodes to control them to take corresponding processing measures. The program flow of the coordinator to establish a network and process node requests is shown in Figure 3.

Figure 3 Coordinator network establishment process

3.3 Router Node Software Design

The role of router nodes in the system is routing and data forwarding. ZigBee devices have two types of addresses. One is the 64-bit IEEE address (also called MAC address or extended address); the other is the 16-bit network address (also called logical address or short address).

ZigBee uses a distributed addressing scheme to allocate network addresses. This scheme ensures that all allocated network addresses are unique in the entire network. The procedure flow of the router establishing a network is shown in Figure 4.

Figure 4 Router network establishment process

3.4 Terminal Node Software Design

The role of the terminal node in the system is to collect power supply voltage data and send the voltage data to the coordinator by establishing a "binding" with the coordinator. At the same time, it receives control commands from the coordinator to control the relays and buzzers in the acquisition/protection module to perform corresponding operations. After the terminal node is started as a terminal and joins the network, it begins to establish a binding with the coordinator. Once a binding is created, the terminal node can send data without knowing the clear destination address. The complete program flow of establishing a binding with the coordinator and transmitting voltage data is shown in Figure 5.

Figure 5 Binding establishment and voltage data transmission process

4. Software Design of Host Computer

4.1 Overall interface design

The host computer software of this system uses the LabWindows/CVI software launched by NI for the measurement and control field as the development platform.

Its main functions include: receiving the voltage data of the monitored power supply from the ZigBee wireless network through the serial port, and displaying the data in real time in the form of text and waveform; setting voltage warning values ​​and control methods, etc., to achieve automatic or manual control of the power supply voltage wireless monitoring system; and storing the voltage and alarm information in the database by connecting to the background database, which is convenient for querying the alarm records on the host computer interface and managing the monitoring data information in the future [8].

The overall design of the interface is shown in Figure 6.

Figure 6 Overall effect of the host computer interface

4.2 Design of interface database functions

This system adds database function to the host computer software. Here, Microsoft Access database is used as the background database to record and manage the monitoring data. LabWindows/CVI provides a database toolkit LabWindows/CVI SQL Toolkit. The toolkit contains a set of advanced functions for completing general database tasks.

5 System operation test

After connecting each module and placing them 10 m apart, first turn on the power supply equipment, then the terminal node starts to collect power supply voltage data and sends the data to the host computer software via the ZigBee network every 1 s. When the voltage is lower than 10 V, the interface is shown in Figure 7.

At this point, the monitoring data has been stored in the background database in real time. When you need to query previously saved alarm records, click the "Database Record Query" tab on the interface, enter the date you want to query the data below, and click OK. The query results will be displayed in a table.

Figure 7 Interface display when voltage is in safe state

6 Conclusion

This paper presents a software and hardware design of ZigBee wireless sensor network for power monitoring system, which solves many problems of wired network such as wiring, maintenance and scalability. The system uses ZigBee wireless module with CC2430 chip as the core as the node, which has the advantages of simple protocol, low cost, low power consumption and easy networking.

The test proves that the system can well complete the tasks of power supply data collection, transmission, processing and recording, and complete the power failure protection work, and has high application value.