Control system for small induction generator based wind turbines

The unpredictable nature of wind makes the design of wind turbines control system a challenging task. Wind turbine system control becomes more difficult when the system is required to connect to the grid. The major issues include connection standard, control system simplicity, cost, reliability, required instrumentation and modes of system operation. A low cost control system and associated instrumentation development is very important for the commercial success of a small grid connected wind turbine. The proposed PIC micro-controller based control system is a good candidate for 3 kW or less grid connected wind power systems. -- The purpose of this thesis is to design a control system for small induction generator based grid connected wind turbines. A PIC16F877 micro-controller is used to connect/disconnect the wind turbine generator to the grid based on real time measurements. The controller is designed and tested for grid connected mode and off-grid mode. The system controller based on the measurements takes decision for grid connection/disconnection or maintains the connection of the system with the grid. Designed controller also takes care of the islanding situation. Such situation occurs in the system while wind is enough to produce power but the grid is absent. The proposed controller will never connect the wind turbine to the grid when grid is absent hence islanding situation will never occur. Low cost instrumentation is also developed to measure the system parameters. -- The designed controller is tested in a laboratory environment using a wind turbine simulator. Wind turbine simulator is an effective platform to evaluate the performance of the wind turbine control system in all possible situations in the lab environment. The proposed wind turbine simulator is based on a 3 kW DC motor. A separately excited DC motor is controlled so that its shaft behaves as a wind turbine rotor. A PI controller is designed which makes sure that the DC motor is producing torque same as wind turbine rotor torque at various wind speeds. -- Soft-starter is also designed to reduce inrush current or surge in current while achieving a proper synchronization between the wind turbine generator and the grid. The designed soft-starter successfully limits the high inrush current during the connection of the wind turbine system to the grid. An experimental investigation is done to find out suitable values of the power resistors for soft-connection of a small wind turbine system to the grid. The designed soft starter limits the initial surge current 1.62 times the rated current of the induction generator. -- While grid is absent, the system controller ceases the power delivery to the grid and connects the wind turbine system to a dump load. However, due to the variation in wind speed the voltage at the load terminal can vary. An electronic PI controller based on phase control relays is developed to regulate the voltage across the dump load while grid is absent. -- The applicability of the proposed system controller for small wind turbines is demonstrated through a number of lab tests. The results show the designed control system is able to control a 3 kW induction generator based wind turbine both in grid connected and off-grid mode

Vibration attenuation by mass redistribution

A nontraditional approach for active structural vibration attenuation was proposed using mass redistribution. The focus was on pendulum structures where the objective was to examine the effectiveness of mass reconfiguration along or within a structure to attenuate its vibrational energy. The mechanics associated with a translating mass along a rotating structure give rise to a Coriolis inertia force which either opposes or increases angular oscillations, thereby producing positive or negative damping, respectively. A strategy of cycling the mass to maximize attenuation and minimize amplification required the mass be moved at twice the frequency of the structural vibrations and be properly coordinated with the angular oscillations. The desired coordination involved moving the mass away from the pivot as the pendulum nears its vertical position and moving the mass towards the pivot when the pendulum nears its maximum angular excursion. System mass reconfiguration was analyzed by studying various mass displacement profiles including sinusoidal, piece-wise constant velocity and modified proportional and derivative action patterns. These strategies were optimized for various time intervals to maximize the rate of energy attenuation or minimize the final energy state. For small amplitude oscillations with sinusoidal mass motion, the dynamic behavior was modeled by Mathieu-Hill equations to explain the beating phenomenon that occurred when the frequency of the mass motion remained constant. Several control systems were designed to generate aforementioned mass reconfiguration profiles. The methodologies included human operator, modified proportional and derivative action, knowledge or rule based and artificial neural network controllers. The human operator system improved with experience and was the most effective. Other systems depended on the chosen parameterization or the implementation of self-adjusting parameters. Several unique tools were developed during the course of this research, as referenced herein

Nonlinear dynamics of two angles subtended by an angle

The work was based from previous analytical results that aims to facilitate rotations. It aims to initially use an elliptical track. However, from previous experimental observations, it was noted that addition of another pendulum, at an angle, instead of introducing a circular track, seemed more effective in inducing rotations. The idea of inducing rotations with a higher range of frequency is intriguing, with rotations being one of the centerpiece of energy generations or mechanical motion. Rotations are used because there is a continuous translational energy as compared to oscillations where it loses energy on it’s peak. If the experiment can induce rotations with impacts present and is still capable of rotating to generate electricity, it could lead to many more possibilities. Renewable energy using vibration is the main approach of this work, and investigating ways to achieve such energy with rotations using electromechanical device is one of the initial conditions that have been chosen to act as a motivation

Modeling of precision motion control systems: a relay feedback approach

Ph.DDOCTOR OF PHILOSOPH