2. Thesis and Dissertations

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    Performance Analysis and Improvement of Power Systems Ring-Down Electromechanical Mode Identification Algorithms
    (National Institute of Technology Karnataka, Surathkal, 2021) Rao, Krishna.; Shubhanga, K N.
    With the commissioning of Wide Area Measurement Systems (WAMS) in large power grids, measurement-based mode identification is finding wide application. From power system stability viewpoint, mode identification from ring-down signals is important. Although ring-down identification algorithms have been studied for a few decades, these still have a scope for improvement. For example, Signal-to-Estimation-error Ratio (SER), which is the recommended fitness metric to compare original and estimated signals in iterative Prony method, sometimes performs suboptimally. So a superior metric is proposed here by combining SER withMean Absolute Percentage Error (MAPE). Another popular ring-down algorithm is matrix pencil, which is normally presented in a non-iterative formulation. It is shown here that iterative formulation of matrix pencil is feasible and is slightly faster than iterative Prony. From the viewpoint of mode identification of noisy signals, Singular Value Decomposition (SVD)-based non-iterative algorithms are reported to be superior. Hence three such algorithms, namely, Total Least Squares matrix pencil (TLS matrix pencil), Hankel Total Least Squares (HTLS) and Eigensystem Realization Algorithm (ERA) are evaluated comparatively. In the process, it is shown that TLS matrix pencil and HTLS algorithms are equivalent. Evident improvement in matrix pencil algorithm performance by incorporation of SVD suggests the same possibility in Prony algorithm. So a customized formulation of Structured Total Least Squares-Prony (STLS-Prony) algorithm is developed for application to power systems. This is compared with two known formulations of SVD-augmented Prony algorithm, namely, Principal Eigenvector-Prony (PE-Prony) and Total Least Squares-Prony (TLS-Prony). A Taylor series-augmented Fourier transform called Digital Taylor-Fourier Transform (DTFT) is examined for its ability to handle exponentially varying sinusoids and a novel concept termed neper response is put forth to characterize the same. It is shown that the computational efficiency of DTFT-based mode identification can be improved greatly by raising the Taylor series order.
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    Design and Control of LowVoltage Dynamic Voltage Restorers employing Semi-Z-Source Inverters
    (National Institute of Technology Karnataka, Surathkal, 2019) Remya, V. K.; Parthiban, P.
    Industries have attained tremendous growth rate in recent years with the advent of computers, sensitive equipment and control systems. Most of the processes involving these devices are disturbed and sometimes damaged by the voltage quality problems. Dynamic Voltage Restorer (DVR) is a power electronic converter based device that protects the sensitive loads from experiencing the power quality problems. The main objective of the research work is to find an alternative to the commonly used Full-Bridge (FB) inverter in the DVR structure. The research work here presents two novel topologies of constant dc-link type DVR based on a) semi-Z-source inverter and b) differential semiZ-source inverter. The semi-Z-source inverter offers the same output voltage range as the FB inverter with reduced number of switches. The differential semi-Z-source inverter gives double the output voltage range with four semi-conductor switches compared to the FB inverter. The Modified Sinusoidal Pulse Width Modulation Technique (MSPWM) is used for generating the switching pulses for the semi-Z-source inverter and differential semi-Z-source inverter. The two DVR topologies proposed effectively mitigate the voltage sag by employing feed-forward control and modified feed-back control. The numerical simulations of the proposed DVR topologies for different voltage disturbances are carried out in MATLAB/ Simulink environment. The application of semi-Z-source inverter and differential semi-Z-source inverter as DVR inverter is validated by the results obtained from the laboratory prototype. The MSPWM for the independent inverter operation, rms voltage method for voltage sag detection and DVR inverter control are implemented in Xilinx-Basys-3 FPGA. The voltage sag generation is implemented using Solid State Relays, transformers and PIC microcontroller. The experimental results of voltage sag compensation by proposed DVR approves the application of semi-Z-source inverter as DVR inverter.