VOLTAGE AND FREQUENCY CONTROL OF SELF EXCITED INDUCTION GENERATOR INTEGRATED WITH SOLAR PV SYSTEM AND BATTERY ENERGY STORAGE

Abstract

Renewable energy mainly wind and solar-based electricity generating systems are becoming increasingly popular for managing energy consumption of remote and isolated communities. Wind and solar are the most promising renewable energy sources (RESs) due to their clean and unbounded supply, low maintenance requirements, lesser mechanical components, no green house gas emission, and ability to be put in remote regions for standalone power generation. The major challenge in wind and solar energy is their unpredictability. The solar system can generate energy during the day time and wind turbine can generate power when the wind speed is high. Therefore, a wind-solar hybrid system is a more reliable power system with battery energy storage (BES). However, due to the intermittent nature of renewable energy, there are power quality issues in the system such as voltage and frequency fluctuations, harmonics distortions, low power factor, and unbalances in the power supply. This thesis work presents power electronics (PE) based solutions to control the voltage & frequency of a wind turbine-driven Self-Excited Induction Generator (SEIG) integrated with a PV system for standalone applications. A voltage source converter (VSC) in the system provides power compensation (active and reactive), harmonics elimination, load leveling, and enhancement in the overall power quality of the standalone generation unit. The proposed system is implemented for both three-phase three-wire (3P3W) and three-phase four-wire (3P4W) isolated supply systems. Maximum Power Point Tracking (MPPT) techniques such as Incremental Conductance (IC) and Perturb & Observe (P&O) have been designed to harvest maximal power from the PV system in both the 3P3W & 3P4W isolated system. The performance parameters of the proposed standalone system have been estimated, and a prototype of the proposed system has been developed and demonstrated in the laboratory to validate the effectiveness of control technologies used in the system. An appropriate control algorithm is needed for the proper operation of PE converters in a wind-solar-based standalone generation system. The control techniques ensure synchronization of different voltages, estimate fundamental components of voltages and vi currents, regulation of DC-link voltage of converters, and charging/discharging of BES.. Different conventional approaches for estimating synchronizing signals have been described, and novel advanced techniques for standalone systems have been proposed. Frequency Locked Loops (FLLs) and Phase Locked Loops (PLLs) are being extensively employed to estimate synchronization signals and can compute the phase, amplitude, and frequency of the load current. These approaches have been implemented under a variety of operating situations, including fluctuations in wind speed, solar intensity and harmonics in the loads for standalone operation of wind-solar hybrid system. Conventional algorithms such as Modified Least Mean Square (MLMS), and Second Order Generalized Integrator (SOGI) based FLL have been used for the proposed standalone system. Furthermore, a novel technique using Second-Order Sequence Filter based FLL has also been proposed, which demonstrate improved performance under unbalanced load conditions. A fast and robust technique based on Delayed Signal Cancellation has been developed, demonstrating accurate frequency estimate and faster dynamic response for the isolated system. The conventional Enhanced Phase Locked Loop (EPLL) and Reduced Order Generalized Integrator (ROGI)-FLL have also been demonstrated, and their performance degradation under dynamic conditions of renewable sources and loads is discussed. Further advanced techniques like a Variable Gain Controller (VGC) and Three-Phase All-Pass Filter PLL based control techniques have been presented, which are adaptive and provide fast dynamic response without compromising steady-state performance. A dual SOGI-based PLL and dual-TOGI PLL for smooth estimation of grid parameters and distortion-free synchronization signals has been also presented. In the present work, the PV system and battery energy storage (BES) are connected at the DC-link of the Voltage Source Converter (VSC) to supply real and reactive power to wind turbine-driven SEIG for standalone applications. A bi-directional dc-dc controller (BDC) is utilized to control the charging/draining modes of BES. The BES is employed to absorb unused power during intermittent conditions and maintain the power equilibrium between the energy sources and load. The dSPACE-1104 controller is being employed for analyzing vii system parameters generating switching pulses for VSC and BDC. The proposed system and algorithms have been simulated and examined in the MATLAB/Simulink environment. The experimental results validate the effectiveness of the proposed control schemes in a standalone system.