Design Of Mixed Power Quality Disturbances Identification System

In recent years, with the rapid development of China’s national economy and thecontinuous innovation of power technology, the number of the electrical equipmentin the grid increases rapidly, including many non-linear, impact, unbalanced load andapplication devices riching in harmonics, although the emergence of these devicesbrings convenience to people’s lives, it also brings serious pollution of power quality,resulting in a variety of power quality problems, the appearance of these problemsoften brings unbearable economic losses to both sides of power suppliers and powerusers, the current power quality can not meet the requirements of both sides of powersuppliers and power users, so how to efficiently manage the existing power qualityproblems and make further improvement has become a hot issue in the field of powersystem at this stage. At the same time, the detection and identification of powerquality disturbances are also increasingly being taken seriously in this field.The existing power quality disturbances identification systems can mostlyachieve recognition of single disturbance, but disturbance signals usually appear inthe form of mixed disturbances during the actual operation of the grid, therefore, thispaper mainly does deep research aiming at the implementation process of mixedpower quality disturbances identification and develop a complete set of powerquality disturbances identification system using LabVIEW software platform. Foralgorithms: At first, adopting Hilbert phase shifter method to achieve accuratepositioning of disturbances signal. The second, adopting wavelet thresholdingtechniques to denoise the located disturbance signal. At last, making use of theimproved HHT algorithm to identify the mixed disturbances signal. During theprocess of mixed disturbances identification, use ensemble empirical modedecomposition algorithm included by improved HHT algorithm to decomposed themixed power quality disturbances into single ones, then determine the type ofdisturbances according to amplitude-frequency characteristics obtained by Hilbert transform. System hardware uses FPGA to control A/D to achieve collection of thepower quality original data, and use SDRAM as data cache, at last transport thecollected data to the a small industrial motherboard for processing through theW5100Ethernet module. For software part, using LabVIEW as the software systemdevelopment platform, and achieve reception and separation of the original samplingdata, disturbance signal positioning and denoising, disturbance decomposition andidentification through its multi-threading technology.The system uses an improved HHT algorithm and successfully achieve theidentification of common mixed power quality disturbances in the grid.Experimental results show that the system has the feature of high real-time and highrecognition accuracy for the mixed power quality disturbances, and laid a goodfoundation for subsequent improvement and management work for the power qualityproblems.