Design And Application Of On-line Power Quality Monitoring Device For Distributed Generation

In recent years, power systems mainly rely on large, centralized power supply to meet the growing demand for electricity, but this way bring environmental issues and blackouts problems, causing huge economic losses to the society. Distributed generation sources usually use wind and solar power or other clean energy. They are environment-friendly and they can compensate the large grid for the lack of stability. Distributed generation gradually attracted people’s attention and continue to increase in the proportion of the grid. Because of its characteristics, distributed generation improved security and stability of the grid, but also brought a number of electricity quality disturbance to the grid, caused a lot of power quality problems.Research for the impact that distributed generation bring to the grid is relatively primitive for now. At the same time, a variety of power quality sensitive electrical equipments are gradually put into use, people have become increasingly demanding on power quality and reliability, which makes the power quality research of distributed generation particularly urgent in this situation. According to the characteristics of distributed generation and actual demands, this paper design an on-line power quality monitoring device applied to distributed generation.This paper analyzed the power quality indicators and discrimination methods, as well as the type of power quality problems that distributed generation bring to the grid, then determined the functional requirements of power quality monitoring device. On-line power quality monitoring device should be capable of measuring basic electrical parameters, transient disturbances and recording SOE events. This paper used Fast Fourier Transform, Wavelet Transform and wide range phase difference frequency measurement method to calculate and analyze power quality problems. To achieve on-line monitoring data and according to the characteristics of distributed generation, this paper design RS-485, Ethernet and GPRS communication functions for the device to achieve interconnection between the power quality monitoring devices. According to the function demand and performance requirements for power quality monitoring system, this paper used STM32F405 and STM32F107 as a dual CPU solution for the device. STM32F405 is based on Cortex M4 core with powerful data computing ability, which is responsible for the signal acquisition and analysis, communicating with STM32F107 via SPI. STM32F107 is mainly responsible for the communication functions, using its own Ethernet module for Ethernet communication, using SIM900A for GPRS wireless communication.This paper used a modular software design according to hardware design of the device. STM32F405’s main functions are divided into:signal acquisition and analysis module, SPI communication module, SOE event processing module, Human Machine Interface module and data storage module. STM32F107 used embedded operating system μC/OS-II and LwIP protocol stack, its functions are divided into: Ethernet communication module, GPRS communication module and RS-485 communication module.This paper analyzed the error of on-line power quality monitoring device and proposed improvement measures, also added anti-jamming design to the device. In the end, this paper carried out a lot of testing, proved that the device can meet the requirements of this design...