ZigBee Substation Monitoring Data acquisition system

0 Introduction

the The country has proposed a "Smart grid" program and has developed a timetable for building a "strong smart grid". "Smart Grid" will achieve the "power flow, information flow, business flow," the integration of a high degree of integration. Intelligent substation is an important foundation and support of strong smart grid, it is in the center of the smart grid hub position. On the receiving of high-voltage power grid input, the next to complete the substation and the user's power distribution, and at the same time to receive the superior dispatching center of information transmission, automatic control, intelligent adjustment and online analysis functions. Therefore, monitoring the operation parameters of the substation helps the power supply department to understand the operation of the substation and the user electricity situation, make the smart grid stronger.

Aiming at the development demand of smart grid, this paper designs a data acquisition system of electric power ZigBee for substation switchgear based on FPGA , and carries out related tests.

1 Application Analysis

1 . 1 SOPC and Nios II technology

SOPC system refers to the use of programmable logic technology to integrate the CPU, memory and other functional modules on a chip, is a special embedded system, with the chip system (SOC) and programmable system features. Industrial automatic control system,DSP, digital communication system and digital logic technology can be integrated, and the software/hardware in the system programmable function. Designers can choose the required function modules from the three Nios II embedded soft cores and more than a few IP cores from the Ahera company, and can also design the required IP cores themselves. Can adjust the performance and cost of the embedded system according to the need, make the product to market quickly, expand the product life cycle, avoid processor renewal. SOPC and Nios II technology enables one or more CPUs to manage a large number of logic circuits in a single chip, with high performance, real-time, highly integrated, reconfigurable, Low development costs and other characteristics will become the future development of embedded systems trends.

1 . 2 system structure and acquisition terminal construction

The system is divided into three parts, namely, FPGA -based acquisition terminal,ZigBee transmission network and data Center host computer, its structure is shown in 1 .

Figure 1 system structure diagram

Collecting terminal is responsible for collecting and preprocessing the power information of substation switchgear, using ZigBee 's multi-hop technology to send data to the data center PC. The data center completes analytical processing of the data, displays the final processing results in graphical and report form, and stores the data as needed.

This paper mainly studies and designs the power data acquisition terminal and ZigBee transmission network of substation switchgear. Using the CYCLONEIII series FPGA chip EP 3C 25Q 240C 8N built on SOPC Technology The control unit of the Data acquisition terminal adopts low cost, low power consumption and transmission stable ZigBee transmission network to transmit the data collected by the monitoring terminal. The Power Information data acquisition terminal of substation Switchgear is the core of the design, including voltage transformer ( knot )/Current transformer (CT), signal conditioning, signal acquisition (AD),FPGA the design of the circuit, and its structure is shown in 2 .

Figure 2 collection Terminal block Diagram

The working process is as follows: The signal from the silicon current transformer enters the signal conditioning circuit first, after filtering, amplification sends to the AD, after the analog-digital conversion signal enters the FPGA through the simple preprocessing, finally will collect the data to pass through The ZigBee Wireless module is transmitted to the remote.

2 Main module design

2 . 1. Design of FPGA module structure based on SOPC

The internal modules of embedded systems using SOPC technology are shown in principle 3 .

Figure 3 SOPC Internal module and external module connection diagram

The system integrates the various modules required for the acquisition terminal on a piece of FPGA . Each module asks for data transfer through the SOPC Internal special Avalon bus structure. This switching architecture supports multiple system architectures, enables simultaneous processing of multiple data, and high throughput for optimal data transfer between modules.

2 . 2 signal acquisition and signal conditioning module

The voltage ( current ) transformer output is often a faint analog signal. The main considerations for amplifier selection in power line monitoring applications are low-noise and low-offset voltage amplifiers. Here, a precision instrumentation op amp with a small offset voltage and good low power BIPBA is chosen as an op amp INA337 for signal conditioning, where the maximum output voltage of the chip can be determined by R4 and the people. Signal conditioning Circuit 4 is shown.

Figure 4 signal conditioning circuit diagram

2 . 3 AD conversion module

Analog-to-digital conversion module is the core of data acquisition system design, whether the design is reasonable is the key to determine whether the whole system can meet the application requirements. This selects AD7656 as the chip for the analog-to-digital conversion module. AD7656 is a 6 -channel successive approximation (SAR) ADC chip with a high level of synchronization sampling, launched by the US AD Company. It can meet the requirements of high resolution, multi-channel, high conversion rate and low power consumption, and has been widely used in power monitoring, instrument control and other systems.

2 . 4 ZigBee Wireless module

A new second generation ZigBee transceiver CC2530 chip is used in the system to construct the ZigBee node. The chip follows the previous CC2430 chip architecture and is used in IEEE 802. A. 4/ZigBee and rf4ce application of a true SOC solution. It is able to build strong network nodes with a low total material cost, combined with the excellent performance of leading RF transceivers, the industry-standard enhanced 8051 core, in-system programmable flash,8KB RAM And many other powerful features. It also has different operating modes to accommodate ultra-low power requirements of the system. In order to improve the transmission performance of ZigBee Wireless module of the coordinator and router node in the network, the cc2530+cc2591 chip combination is used to extend the communication distance of the existing ZigBee transmission module.

3 Software Design

3 . 1 Design of control flow based on Nios Soft Core

The data collection and transmission of the power data acquisition terminal for substation Switchgear is shown in Flowchart 5 . The program begins by initializing the system's control register and some peripherals, then determining if there is an interrupt signal and determining the type of interrupt, and if the switch is interrupted, it enters the control module of the switching volume, and the analog data obtained by the sensor is entered into the human conditioning module and A/D conversion, which is the main range selection in this module and the conversion of the analog amount to a digital amount. At the same time, the converted digital quantity exists in SRAM memory, which is processed and analyzed by the data processing and Operation module. The results of processing and analysis are passed through ZigBee transmission network to the host computer for further processing.

Fig. 5 Control flow of Nios Soft Core

3 . 2 ZigBee Digital transmission module Send data flow

The system has real-time transmission function of substation monitoring data, which is realized by software design of ZigBee Digital transmission module. After the node is power up, the monitoring device and the ZigBee RF transceiver begin to initialize. First, the ZigBee Digital transmission module to check the ZigBee Data Acquisition module and the communication between the router. Normally, theZigBee wireless module starts sending data. Then check that the ZigBee module sent the data is successful, if not correct or unsuccessful resend. After the data is sent correctly, the data is transmitted to the terminal equipment by the coordinator, and the analysis and display function is done by the terminal data processing equipment. ZigBee sends data flow 6 as shown.

Figure 7 Three-phase active power Change curve

4 Monitoring of the environment and monitoring data

4 . 1 monitoring environment

In order to verify the feasibility of the system, a coal mine substation was selected for testing work. The substation is powered by a single-bus segmented mode, and two transformers are supplied in one supply, with a capacity of. 5MVA. The upper line power supply is 35kV bus, and the transformer becomes 6kV bus to power the whole factory load. The main load of 6kV busbar is mainly shaft hoist, auxiliary shaft hoist, blower, pressure fan, water pump, factory lighting and downhole load. Monitoring time for a normal working day :xx to xx:

4 . 2 Partial experimental data and waveforms

The system sets up the analysis software in the data center host computer, and displays and analyzes the power information monitoring data of substation switchgear in the form of reports and graphs.

Figure 7 Three-phase active power Change curve

Figure 7 is a partial three-phase active power real-time change curve. It can be seen that the monitoring of the switch cabinet connection load changes more intense, intense duration of about two minutes. In general, the hoist in the coal mine is the main load of the substation, and it has a lifting cycle of about two minutes. According to the change of the image data, the real-time situation of power information in substation switchgear is verified by the system. The figure can be obtained by comparing the maximum and rated power to see if the maximum load has been reached.

5 Concluding remarks

Using FPGA and SOPC technology to collect power information of switchgear, using ZigBee Wireless module for data transmission, the specific software and hardware design scheme and process are put forward, and the transmission test experiment is carried out.

The test results show that the system can monitor the power information of switchgear in time, so as to make timely processing. In the transmission experiment, theZigBee Digital Transmission module can transmit accurately the measured data of the substation, and show the good transmission ability. It can meet the requirements of real-time data in substation monitoring, realize the wireless and intellectualization of data acquisition of ZigBee in substation, facilitate the staff to grasp the operation situation and make corresponding control in time, which has high application value in the smart grid.

ZigBee Substation Monitoring Data acquisition system