Control system for small induction generator based wind turbines.

摘要

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 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 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 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.