Fault Detection and Classification using Wavelet and ANN in DFIG and TCSC Connected Transmission Line

This paper presents fault detection and classification using Wavelet and ANN based methods in a DFIG-based series compensated system. The state-of-the art methods include Wavelet transform, Fourier transform, and Wavelet-neuro fuzzy methods-based system for fault detection and classification. However, the accuracy of these state-of-the-art methods diminishes during variable conditions such as changes in wind speed, high impedance faults, and the changes in the series compensation level. Specifically, in Wavelet transform based methods, the threshold values need to be adapted based on the variable field conditions. To solve this problem, this paper has proposed a Wavelet-ANN based fault detection method where Wavelet is used as an identifier and ANN is used as a classifier for detecting various fault cases. This methodology is also effective under SSR condition. The proposed methodology is evaluated on various fault and non-fault cases generated on an IEEE first benchmark model under varying compensation levels from 20% to 55%, impedance faults, and wind velocity from 6m/sec to 10m/sec using MATLAB/Simulink, OPALRT(OP4510) manufactured real-time digital simulator environment, Arduino board I/O ports communicating with external PC in which ANN model dumped, using Arduino support package of MATLAB. The preliminary results are compared with the state-of-the-art fault detection method, where the proposed method shows robust performance under varying field conditions

A New Relaying Method for Third Zone Distance Relay Blocking During Power Swings

Due to the increasing complexity of modern bulk power systems, the power swing identification, blocking, and protection have become more challenging than they used to be. Among various transmission line protection methods, distance relays are the most commonly used type. One of the advantages of using distance relays is the zoned protection which provides redundancy. However, the additional redundancy comes with a problem that it increases the probability of incorrect operation. For example, the undesired operation of the third zone distance protection during power swing scenarios has been attributed as one of the major causes for creating large-scale blackouts. Some research works in the literature investigate proper identification of stable and unstable power swing conditions. Most research works dwell on identification of power swing conditions but do not address how the scheme could be used for blocking the third zone of distance relays during stable power swings. Also, the current power swing detection schemes are often very complex to implement for a relaying engineer or are not fast enough for blocking the third zone distance element. This research proposes a reliable and fast methodology for the third zone blocking (TZB) during power swings. The new mathematical formulations and derivations are based on sound time tested power system theory and are simpler to understand for a relaying engineer to implement this technique. The algorithm proposed in the research can prevent unnecessary tripping of distance relays during power swings. The algorithm also overcomes the shortcomings of the conventional power swing identification methods when applied for the third zone blocking. A first zero-crossing (FZC) concept is introduced as the criteria for identifying stable power swing or out-of-step phenomena. The analysis is based on system stability point of view and utilizes power-angle equations. The proposed algorithm could be applied at every discrete time interval or time step of a distance relay to detect power swing points. It could also be applied to any transmission line in the power system by finding an equivalent single machine infinite bus (SMIB) configuration individually for each line on a real-time basis, which is one of the primary advantages of the proposed method. In the thesis work, the proposed technique is first demonstrated using a simple single machine infinite bus system. The TZB algorithm is then tested using a modified Western Electricity Coordinating Council (WSCC) power system configuration using Power System Analysis Toolbox (PSAT) simulations. The code is written in MATLAB. The TZB method is then further analyzed using electromagnetic simulations with Real-Time Digital Simulator (RTDS) on WSCC system. The proposed method uses small time step simulations (50 μs) to take various aspects of power system complexity into consideration, such as different harmonics presents in the system, synchronous machine operation at different speeds, travelling wave representation of transmission lines instead of purely lumped parameter representation, etc. The investigations as mentioned above and the results show that the proposed TZB scheme is a straightforward and reliable technique, involving only a few calculation steps, and could be applied to any power system configuration. The main novelty of this technique is that it does not require a priori stability study to find the relay settings unlike conventional power swing identification or distance relay blocking techniques. The inputs to the relay are basic electrical quantities which could be easily measured locally on any transmission line. The local measurements would make the implementation of the proposed TZB simpler for relaying applications compared to Wide Area Measurement System (WAMS) based techniques. In a WAMS based relaying technique - the cost associated with the communication network, reliability of the communication network, impact of communication delay on relay, etc all become factors for actual industry use

Modeling and Simulation of Protective Relay for Short Circuits in AC Micro-grids using Fuzzy Logic

The duo of high human appetite for electricity in the 21st century and high human population growth rate entail inadequacy of contemporary electric power protective systems for the emerging micro-grid. This thesis presents results of a research which seeks to propose a new model of protective device for short circuits in ac micro-grids. Response of the proposed relay is consistent with a reliable device. Consequently, a protective relay for short circuits in micro-grids is proposed

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Measurements, Models, Systems and Design

531 s.

A Review of Control Techniques for Wind Energy Conversion System

Wind energy is the most efficient and advanced form of renewable energy (RE) in recent decades, and an effective controller is required to regulate the power generated by wind energy. This study provides an overview of state-of-the-art control strategies for wind energy conversion systems (WECS). Studies on the pitch angle controller, the maximum power point tracking (MPPT) controller, the machine side controller (MSC), and the grid side controller (GSC) are reviewed and discussed. Related works are analyzed, including evolution, software used, input and output parameters, specifications, merits, and limitations of different control techniques. The analysis shows that better performance can be obtained by the adaptive and soft-computing based pitch angle controller and MPPT controller, the field-oriented control for MSC, and the voltage-oriented control for GSC. This study provides an appropriate benchmark for further wind energy research

OUT-OF-STEP DETECTION BASED ON ZUBOV’S APPROXIMATION BOUNDARY METHOD

Disturbances in power systems may lead to electromagnetic transient oscillations due to mismatch of mechanical input power and electrical output power. Out-of-step conditions in power system are common after the disturbances where the continuous oscillations do not damp out and the system becomes unstable. Existing out-of-step detection methods are system specific as extensive off-line studies are required for setting of relays. Most of the existing algorithms also require network reduction techniques to apply in multi-machine power systems. To overcome these issues, this research applies Phasor Measurement Unit (PMU) data and Zubov’s approximation stability boundary method, which is a modification of Lyapunov’s direct method, to develop a novel out-of-step detection algorithm. The proposed out-of-step detection algorithm is tested in a Single Machine Infinite Bus system, IEEE 3-machine 9-bus, and IEEE 10-machine 39-bus systems. Simulation results show that the proposed algorithm is capable of detecting out-of-step conditions in multi-machine power systems without using network reduction techniques and a comparative study with an existing blinder method demonstrate that the decision times are faster. The simulation case studies also demonstrate that the proposed algorithm does not depend on power system parameters, hence it avoids the need of extensive off-line system studies as needed in other algorithms