Research on fault diagnosis of UPFC based on wavelet packet energy

In order to make up for the lack of UPFC protection system in fault diagnosis and early warning, a new UPFC fault diagnosis method based on wavelet packet energy and OVO SVM has been proposed. During the simulation, the signals of DC side capacitor voltage of the UPFC model in the states of normal and 4 shunt valve side internal fault are collected. The wavelet packet analysis is used to decompose the signal into three layers and the wavelet packet energy of each frequency band is extracted to form the original sample space. The sample data are filtered by principal component analysis (PCA) algorithm to filter out the effective fault information. Then the data after dimension reduction are sent into one-versus-one SVM (OVO SVM) for training and testing. Experiments prove that the 5 running states of UPFC mentioned above can be identified in a very short period of time effectively and accurately by this UPFC fault diagnosis technology and to some extent, the safe and stable operation of UPFC is able to be prospectively guaranteed.

I. Introduction

The Unified Power Flow Controller(UPFC), which is able to independently, rapidity, precisely and continuously control system voltage and power flow, is one of the third generation devices of Flexible Alternative Current Transmission Systems(FACTS) with the best universal property and the most comprehensive function so far [1]–[3]. As UPFC becomes the hotspot of electrical engineering research realm, starting from the concept of UPFC proposed by Dr. L. Gyugyi in 1991and only 7 years later, the world's first large capacity of commercial UPFC has already been successfully put into operation in the United States. At present, the converters of the UPFC that has been put into operation have voltage balancing problems because of devices in series and PWM is used to improve the quality of the voltage waveform. Whereas high frequency makes the switching frequency high and lead to the switching loss which means the safe and stable operation of UPFC is under threatened [4]–[5]. Nowadays, the researches on UPFC faults at home and abroad are mainly focused on the faults and the corresponding management methods of transmission and compensation lines with UPFC [6]–[8], the grounding design and fault characteristics of UPFC [2]–[9] and the corresponding protection schemes for UPFC fault characteristics [10]–[11]. However, there are few studies involving the diagnosis strategy for UPFC faults on itself and its components.