Harmonic control system of smart meter based on ZigBee

Under the background that the country vigorously advocates the development of smart grids, the first step is to develop smart meters. In order to achieve smart grid harmonic pollution control to compensate for non-function rate and reduce energy consumption, while monitoring power quality in real time, this paper proposes a ZigBee-based Communication protocol, using ADE7878 energy measurement embedded into STM32 unit to use the CC2430 of the meter node and Ethernet to transmit data and perform power quality analysis. The analysis results are combined with harmonic suppression algorithms to control the power quality controller to achieve power harmonics Governance. Supported by “the Fundamental Research Funds for the Central Research Funds for the Central”: 201910497134


Introduction
Single-phase power quality real-time monitoring system based on ZigBee ADE7878 electric energy measurement module as the core, to the user's real-time power quality (voltage current instantaneous value, RMS, apparent power, reactive power, active power, electricity consumption, transmission power, over voltage, over current, and power phenomenon) measurement, embedded STM32 unit of measurement information after reading through the SPI bus, use of electric meter node CC2430 will gather in node, data transfer to CC2430 convergence node through Ethernet switch sent to monitoring terminal, complete the data transmission, After the monitoring terminal receives the data, the power quality is analyzed, and the power quality controller is controlled by combining the analysis results with the harmonic suppression algorithm [1], so as to change the harmonic component of the current electric energy. At the same time, users can control the LCD screen of smart electricity meter through infrared operation to understand the current electricity consumption. Its system block diagram is shown in Figure  1.  Figure. 1. Design drawing of single-phase power quality real-time monitoring system.

System design of intelligent electricity meter nodes
Intelligent meter node is based on embedded hardware platform, mainly composed of ADE7878 power measurement, relay control, infrared control and LIQUID crystal display modules, using C/OS-II operating system to complete task management [2]. After testing the wireless sensor network of CC2430, the reliable transmission distance of CC2430 core module in open area is 150 m. Considering the size and area of the small area, a sink node is designed every 3 floors, and the data of the ZigBee sink node is shared through the Ethernet conversion module in the local area network. This ensures the reliability of the data.

Design of harmonic control system
This system combines passive filter and active filter, which can not only solve the problem of using passive or active filter alone, but also reduce the capacity of active filter. Favorable for popularization and application in power systems. [3] The harmonic control system is shown in Figure 2.

Upper computer monitoring terminal and embedded control
The design of the upper computer real-time monitoring terminal of the system is mainly composed of four parts: system data storage and processing, real-time monitoring and charge management, intelligent control of the system as a whole, real-time waveform display.

System data processing
Considering the multiplicity of data and real-time updating, the speed and efficiency of the algorithm are of great significance. Traditional DFT and integral algorithms have some limitations. FFT reduces the amount of computation by selecting and rearranging intermediate results [4]. In the computer, the time and distance of multiplication operation is greater than the specific addition operation, so taking multiplication as an example, the direct DFT complex multiplication times is N2, FFT is, the ratio of When N= 32, the amount of FFT calculation is 12.8 times that of DFT.When the sampled data is 1024 points or more, the FFT algorithm saves about 50% of the computation compared with the DFT transformation.

Real-time monitoring
The real-time monitoring interface displays the user's meter quality data, current FFT spectrum diagram and voltage current phase difference.The horizontal axis of the spectrum represents the DC component, the fundamental wave, and the second harmonic [5]... Fifteen harmonics. The two representations of the spectrum diagram are shown in Figure3. In the current FFT spectrum diagram, the current size is related to the amount of load, the system can be clearly displayed using the intelligent dimension of the number line. In case of power theft, high voltage or current, problems with quality parameters of the grid, or arrears of user fees, the system will alarm and display the specific situation.

Real-time display of waveform
Considering that in the actual situation, the terminal of the power grid may need to check the numerical change of some electric quantity parameters of a certain user, this system displays the electric quantity of the user clearly and beautifully through a virtual oscilloscope, and the waveform can adjust the scale change according to the amplitude, voltage and current waveform real-time display is shown in Figure 4.