Internet of Things (ZigBee) contract energy management

Due to the superior characteristics of ZigBee, wireless networking based on ZigBee technology is a more suitable means of implementing downlink channels. Suitable for some short-distance wireless networks, such as wireless meter reading networks such as office buildings, office buildings, dormitory buildings, and factories. It is suitable for enterprise internal energy consumption monitoring and management systems, especially for old buildings with difficult wiring. Energy consumption management system. And if it is combined with mature industrial Ethernet and GPRS / CDMA upstream channels, and a complete collection and monitoring system with the background management master station, it can provide an effective solution for remote management. See Table 1 for a comparison of ZigBee and other last-mile communication technologies.

Table 1 Comparison of ZigBee and other "last mile" technologies

The ZigBee protocol is based on the IEEE 802.15.4 standard. From 2004, ZigBee V1.0 was released to the latest ZigBee 2006 version with the ZigBee-PRO extended instruction set added. ZigBee has a powerful device networking function (see Figure 1), which supports three main types of self-organizing wireless networks, namely, star structure, mesh structure, and tree structure (Cluster Tree), especially The mesh structure has strong network robustness and system reliability. Compared with the currently widely used short-distance wireless communication technologies such as Wi-Fi and Bluetooth, ZigBee has the main features.

Figure 1 Zigbee network topology classification

(1) Short working cycle, low power consumption for sending and receiving information, and RFD (Reduced Function Device, simplified function device) adopts sleep mode, you can enter sleep mode when not working.
(2) Low cost. By greatly simplifying the protocol (less than 1/10 of Bluetooth), the requirements for the communication controller are reduced. Based on the 8051 8-bit microcontroller, the full-function master node requires 32KB code, and the sub-function node is as little as 4KB code .
(3) Low rate and short delay. The maximum communication rate of ZigBee reaches 250 kb / s (working at 2.4 GHz), which satisfies the application requirements of low-rate transmission data. ZigBee's response speed is relatively fast, generally only 15ms to go from sleep to working state, only 30ms to connect the node to the network, further saving power. In comparison, Bluetooth requires 3 to 10 S, and Wi-Fi requires 3 S.
(4) Close range and high capacity. The transmission range is generally between 10 and 100 m. After increasing the RF transmission power, it can also be increased to 1 to 3 km. This refers to the distance between neighboring nodes. If relayed by routing and communication between nodes, it will reach several hundred meters or even several kilometers after expansion. ZigBee can adopt star, sheet and mesh network structures. A master node manages several child nodes, and at most one master node can manage 254 child nodes.
(5) High reliability and high security. Zigbee's Medium Access Control (MAC) uses the CSMA / CA collision avoidance mechanism, and reserves dedicated time slots for communication services that require fixed bandwidth to avoid competition and conflicts when sending data. ZigBee also provides a 3-level security mode, including no security settings, access control list to prevent illegal access to data, and a symmetric password using Advanced Encryption Standard (AES) to flexibly determine its security attributes.
(6) License-free frequency band. Direct sequence spread spectrum is used in the Industrial Scientific Medical (ISM) bands, which are 2.4 GHz (global), 915 MHz (United States) and 868 MHz (Europe).

ZigBee performance parameters
The main parameters of ZigBee collector / terminal are shown in Table 2.

Table 2

The meaning of contract energy management
Contract energy management is a service mechanism generally implemented in developed countries that uses market measures to promote energy conservation. Energy-saving service companies sign energy management contracts with users to provide users with services such as energy-saving diagnosis, financing, and transformation, and to recover investment and obtain reasonable profits through energy-saving benefit sharing, which can greatly reduce the capital and technical risks of energy-saving transformation of energy-consuming units. Mobilizing the enthusiasm of energy-saving units in energy-saving transformation is an effective energy-saving measure. According to the "Energy Conservation Law of the People's Republic of China" and the "Decision of the State Council on Strengthening Energy Conservation Work" (Guo Fa [2006] No. 28), and "Notice of the State Council on Issuing the Comprehensive Work Plan for Energy Conservation and Emission Reduction" (Guo Fa [2007] 15 No.) and other document spirits, it is an inevitable trend to accelerate the implementation of contract energy management and promote the development of energy-saving service industry.
The Ankerui contract energy management system combines the advantages of its own product research and development, and adopts one or more optimized networking methods based on fieldbus or wireless communication according to the actual situation on the spot to achieve remote power distribution monitoring, energy collection and copying. Quality management also saves users a large amount of one-time investment cost. The system configuration platform developed by the company integrates various domestic and international industrial field communication protocols, such as IEC60870-5-101 / 102/103/104, CANBus, PorfiBus, DNP, CDT, ModBus, etc., as well as the latest IEC61850 communication system. It supports the access of a large number of third-party intelligent equipment or imported equipment. The advanced system architecture supports information sharing and Web publishing, which solves the problem of distribution monitoring information islands. The automatic generation of expert reports greatly reduces the workload of duty personnel and improves the efficiency of energy-saving management.

The metering system of the energy management system should choose the power meter
To establish a contract energy management system, a measurement system should be established first. Data comes before decision, and energy saving starts with measurement. In order not to duplicate investment and cause waste, the energy management system should be integrated with the power distribution system, and energy consumption data should be collected directly in the power distribution system.
Electric energy metering should adopt electric meters as internal management meters, and should not use charge meters. See Table 3 for a comparison of toll meters and power meters. In power management, the power supply department usually installs charged meters at the main entrance. Considering the needs of internal energy metering and energy-saving management, power meters are installed on the basis of users installing toll meters for internal energy management. Therefore, users can choose to purchase independently, but should pay attention to whether the manufacturer has a measurement license for power meters (electric energy part). The power meter can complete the collection of the itemized energy data of each loop and each functional area, and complete the itemized energy measurement through the background energy management system.

Table 3 Comparison of toll meters and power meters

ZigBee wireless meter reading solution
Whether it is wired or wireless, the meter reading system is always affected by factors such as environment, distance, and occasions, and each has its own different solutions. The meter reading system based on Zigbee will not deviate from this constraint, it will also be affected by factors such as environment, distance and occasion, and there are different solutions. Because ZiBbee's positioning is short-distance communication, when it is applied to wireless meter reading networks such as office buildings, office buildings, dormitory buildings and factories, it has relatively few factors to consider.
The entire system composed of a single subnet of the ZigBee wireless collection system is the same as the composition of the system architecture described above, mainly composed of the upstream network industrial Ethernet and the downstream network ZigBee wireless local area network. The entire subnet is mainly composed of electricity meters, ZigBee collectors and ZigBee network terminals. The electric meter can use ACREL's 1352 series of card-type electric energy meters and ACR network power meters, etc. They use RS485 communication with the ZigBee collector, and use the MODBUS communication protocol; up to 32 meters can be connected under the ZigBee collector; Up to 255 tables can be connected in the entire ZigBee subnet; in order to ensure the reliability of the communication connection, sometimes depending on the environment and distance, it is necessary to add a few more network nodes with routing functions (the ZigBee collector is configured as a routing function), In order to ensure that the communication of some remote nodes is normal; in addition, considering the congestion degree and real-time transmission of the wireless network, it is recommended that the number of wireless nodes (ie ZigBee collectors) in the entire subnet should not be greater than 60, so as to ensure the network Communication quality. Each ZigBee subnet has its own ID identification and frequency band division, which can help expand more table counts.

Application Example of Energy Management System Based on ZigBee Contract
Figure 2 shows the ZigBee energy management system. The remote communication network uses an industrial Ethernet network, and the communication protocol of the meter in the network uses the MODBUS-RTU protocol. The monitoring host in the entire system transmits the MODBUS-RTU command data to the ZigBee network center node through Ethernet according to the TCP / IP protocol. The network center node then transmits the command data frame to the broadcast mode through the single-point to multi-point communication mode. Each ZigBee collector in the ZigBee wireless network is passed to each meter on the 485 bus through the ZigBee collector. If the address of the meter matches the address involved in the command frame, a corresponding data reply is made and the original path is used. Return to the monitoring host.

Figure 2 ZigBee energy management system

The whole system can monitor the energy measurement of various sub-items of the entire plant or the whole building, such as the power consumption of street lamps in a plant, the power consumption of various offices and the power consumption of various production lines, etc., and can also be in the form of reports Analyze the percentage of total energy consumption of each sub-item of the factory over a period of time, so that the factory can understand the energy consumption of each sub-item during this period of time to formulate a future energy management plan to achieve energy conservation and reduction Consuming effect.
At present, the entire system is implemented in Jiangsu Ankerui. According to the principle of sub-metering, the incoming and outgoing lines of the plant are sub-metered. The power distribution system in the plant monitors all incoming circuits and uses them all. The Zigbee acquisition module performs data acquisition and monitoring, including parameters such as current, voltage, and energy, and some simple on-off control. The system also monitors some branches, such as production lines, office buildings, and air conditioners, to monitor the various data in a comprehensive manner, so that the factory can understand various data in order to formulate more detailed energy-saving programs.
The project's entire ZigBee energy management system uses 21 wireless modules, including 82 blocks of various meters. Among them, the 14 meters in the power distribution room are connected to a ZigBee acquisition module for wireless communication through the 485 bus. Each air-conditioning socket is more dispersed, and each uses a ZigBee acquisition module, etc. According to the discrete situation of the meter, the 485 bus is used to connect a module together, and the modules are connected separately. This method is more flexible and reduces the difficulties caused by wiring.
The whole system is running well and has been running on site for a while. Real-time reflects the current situation of the plant during this period, thus reflecting the load situation of the entire plant area.

Conclusion
Energy is becoming increasingly tight, energy saving and consumption reduction is an inevitable choice for social development, and the contract energy management system provides users with a good mechanism. The establishment of a measurement system for energy management through Zigbee wireless modules and power meters can reduce repeated investment, save wiring, and integrate intelligent power monitoring and energy management for users. The system is running in projects such as the Expo VIP Hotel, Suzhou Pioneer Park and Guangzhou Asian Games Tennis Center, and has achieved good social and economic benefits.

The article comes from: "Electric Times", Issue 1, 2011.

About the Author:

Yu Jing, female, undergraduate, engineer of Wuhan Ankerui Electric Co., Ltd., the main research direction is intelligent power monitoring and power management system

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