In remote areas,to produce electricity from wind energy Self Excited Induction Generators(SEIG) are extensively used.
This paper presents simulation and experimentation of stand alone Self Excited Induction Generator(SEIG) and terminal voltage control of induction generator.The system consists of constant voltage controller, Pulse-Width modulated voltage source inverter and a start up battery.With the help of control strategy,DC link voltage is maintained constant inspite of changes in load .Thus Induction Generator can be operated at constant voltage from no-load to full-load. Mathematical modelling of Self Excited Induction Generator,Induction Motor(IM) and wind turbine are done using matlab/simulink and hardware implementation is done for the same using TI’s F28069M launch pad under varying load conditions.With an ever increasing demand of energy and global warming,renewable energy sources have gained more importance and are becoming more and more popular.
Wind is a plentiful, abundant and an eco-friendly renewable energy.Many energy conversion technologies have been developed to harness the wind energy.Induction Generators(IG) are widely used to generate electricity from wind in remote/isolated areas.Induction machines have many advantages for wind power plant due to its easy operation as either motor or generator, robust construction,low cost and self protection against faults and overloads.Thus Induction Generators have become more popular than other machines.The only disadvantage of IG is the necessity of excitation power. There are various methods of supplying reactive power.
In self excited mode three phase delta connected capacitors are connected to the induction generators to provide the required reactive power.This kind of arrangement suffers from poor voltage regulation and is suitable for constant load at IG terminals and for a constant mechanical speed.Also it requires a large capacitor bank.In order to overcome this problem and to have more emphasis on terminal voltage regulation, many methods have been proposed.3 presents voltage build up process for astand alone SEIG with PWM-VSI.4 demonstrates the transient performance of a series compensated three phase self excited induction generator feeding dynamic load.
5 proposed a DSP based constant voltage controller for a stand alone wind energy conversion system.Terminal voltage is maintained constant with the control strategy even when there is change in load from no-load to full-load. In this paper a simple sensor less,low cost control strategy is proposed.Terminal voltage is controlled by sine PWM VSI. The block diagram representation is shown in the fig 1. The induction machine is driven by a constant speed prime mover. The terminals of the stator are connected to a PWM VSI.
The DC side of the VSI is connected to a capacitor. The initial charge on the capacitor provides the initial magnetizing flux to the machine. Once the machine runs as generator it charges the capacitor, and under generating mode the VSI works like a rectifier. AC load is connected across the stator terminals of the machine and any change in the load would affect the capacitor DC voltage. This drawback is overcome by adjusting the stator frequency accordingly.
Here the output is a DC voltage and a control system isrequired to keep this DC voltage at constant level. Once this is achieved a DC load can use it directly. The other advantage would be, the DC voltage can be utilized if the generator in times incapable of meeting the heavy power requirement of the AC load connected across the stator terminals.Here such a model is mathematically built which can maintain a constant DC voltage across the capacitor even though the load is subjected to variations and is simulated in MATLAB/SIMULINK.
The system includes modeling of Induction machine, sine PWM-VSI and a control loop. Induction machine is modeled using d-q axestheory in stationary reference frame.