Research On Power Quality Detection Methods And Application

In order to improve the power quality of power system, a accurate and realtime monitoring system is necessary. This dissertation focuses on the features of power system and designs a power quality motoring system. The algorithms are studied to detect the inter harmonic, voltage fluency and flicker realtime. The main achievements is listed as following.1. After studying the detect methods of inter harmonic carefully, this dissertation put forward to use the ZOOM FFT method to detect the inter harmonic. This method can meet the requirement of realtime and the accurate is very high, at the same time the computation is not very big. It is very suitable to the realtime system .2. This dissertation study the square demodulation proposed by IEC, this method may cause some error when the modulated wave is square. A new demodulation method is proposed, this method can over the defect of IEC method and the computation is increase limited.3. A new flicker based on frequency domain is proposed. The flicker detection method proposal by IEC is inaccurate when the frequency is low. This method has high accuracy at low frequency band overcome the defect of IEC method. In order to avoid the error caused by frequency leakage and improve the frequency resolution the Chirp Z transform is used.4. The power quality detection device has it's special requirement, when the device is working it has to deal with very big computation and fast data transform. So we choose DSP+PCI+computer as the main structure. A DAQ which has a DSP chip is design, this card has DSP chip and PCI bridge. The sampled data is processed by DSP and the result is transformed to computer by PCI bus. By this way the computer is free from computation. The computing power of DSP and abundant resources of computer is combined.5. According to the requirement of power quality detection device the software is designed. We put the detection device in test, the test result prove the power quality designed by this dissertation can meet the requirement.