A vertical (or horizontal) wind turbine is coupled to the shaft of a squirrel cage induction generator through a speed up gear ratio The variable frequency variable voltage power from the generator is rectified by a PWM IGBT rectifier (Ismai,2015). The rectifier also supplies the excitation need of the machine. Salient advantages of the converter system include the following.
i. Line side power factor is unity with no harmonic current injection
ii. The cage type induction machine is extremely rugged, reliable, economical, and universally popular.
iii. Machine current is sinusoidal and no harmonic copper loss.
iv. Rectifier can generate programmable excitation for the machine.
v. Continuous power generation from zero to highest turbine speed is possible.
vi. Power can flow in either director permitting the generator to run as a motor to startup.
vii. Autonomous operation of the system is possible with either a start-up capacitor or with a battery on the dc link.
viii. Extremely fast transient response is possible.
ix. Multiple generators or multiple systems can be operated in parallel.
x. The inverter can be operated as a VAR/harmonic compensator when spare capacity is available.
Fig. 2.2: A voltage fed double PWM converter wind generation system
Both horizontal and vertical axis wind turbines are used in wind generation systems. The vertical Darrieus type has the advantages of being located on the ground and accepting wind from any direction without any special yaw mechanism. It is, therefore, preferred for high power output. The disadvantages are that the turbine is not self-starting and there is a large pulsating torque which depends on wind velocity, turbine speed, and other factors related to the design of the turbine. ( HU,2014). The aerodynamic power of a vertical turbine is given by the equation:
The power coefficient is the figure-of-merit and is defined as the ratio of actual poor delivered to the free stream power flowing through a similar but uninterrupted area, and tip speed ratio (TSR) is the ratio of turbine speed at the tip of a blade to the free stream wind speed. The parameter is a nonlinear function of ? (. Laudani,2014). The oscillatory torque of the turbine is more dominant at the first, second, and fourth harmonics of fundamental turbine angular velocity and is given by the expression:
TOSC = Tm (ACOS (wmt) + BCos(2wmt) + CCos(4wmt) (2.4)
Where, A.B,C are the constants.
Fig.2.3 :Model of wind turbine with oscillatory torque
The turbine torque as a function of angular wind velocity is shown in result fig. 5.8.
The machine and inverter output currents are sinusoidal, as shown in fig.2.3. The machine absorbs lagging reactive current, but it is always zero on the line side: i.e., the line power factor is unity. The rectifier uses indirect vector control in the inner current control loop, whereas the direct vector control method is used for the inverter current controller. Vector control permits fast transient response of the system . (Rajasekar,2015). The generator speed is controlled by indirect vector control with torque control and synchronous control in the inner loop. Since an increase of Po causes a decrease of DC link voltage, the voltage polarity loop has been reversed. For a particular wind velocity Vw, there will be an optimum setting of generator speed wr*. The speed loop will generate the torque component of machine current so as to balance the developed torque with the load torque. The variable voltage variable frequency power from the super-synchronous induction generator will be rectified and pumped to the dc link. The dc link voltage controller ill regulate the line power Po so that the link voltage always remains constant. A feed forward power signal from the machine output to the dc voltage loop prevents transient fluctuation of link voltage.
2.6 Theory of work
To design a membership function that analysis the faults in power generation. There is a lot of faults in power companies like overcurrent, distortion, harmonic to mention a few. This can be overcome by designing a membership function that analysis the faults and provides a solution to it.
Fig. 2.4: Fuzzy control FLC-1 and FCL 2 operation showing maximization of line power.
“Optimization” comes from the same root as “optimal”, which means best. When you optimize something, you are “making it best”.
But “best” can vary. If you’re a football player, you might want to maximize your running yards, and also minimize your fumbles. Both maximizing and minimizing are types of optimization problems.
Mathematical Optimization is a branch of applied mathematics which is useful in many different fields. Here are a few examples:
The basic optimization problem consists of…
•The objective function, f(x), which is the output you’re trying to maximize or minimize.
•Variables, x1x2x3and so on, which are the inputs –things you can control. They are abbreviated xnto refer to individuals or x to refer to them as a group.
•Constraints, which are equations that place limits on how big or small some variables can get. Equality constraints are usually noted hn(x)and inequality constraints are noted gn(x).
2.7 Research Gap
Lastly, following the above Research procedures and recommendations, I noticed that there was a gap left to be filled during the impact of integrating renewable energy sources for rural electrification using an intelligent agent. That was the reason I had to use an optimized intelligent agent other than ordinaryintelligent agent or with PI controller which are not flexible as its inputs once given can’t be changed. The optimized intelligent agent introduced in this report is part of the energy power generation for rural electrification ; works better than the PI controller in terms of flexibility, speed and reliability for reduction of voltage fluctuations, harmonic distortions and low power factor to its lowest minimum value thereby enhancing stable power supply in the rural areas.
METHODOLOGY, DESIGN AND IMPLEMENTATION