ENGR7762 Renewable Energy Systems Practical 1: Grid-Connected Wind Turbine

The aim of this practical is to evaluate basic operating characteristics of a Doubly-fed- induction generator using the standard MATLAB/Simulink blocks given in SymPowerSystems.

Familiarise with the block diagrams of MATLAB/Simulink.
Develop a simple model of a wind power plant directly connected to a load and grid. Run simulations and familiarise with MATLAB Workspace and graph plotting.

In contrast to a conventional power generation, wind power is intermittent type, thus the output power of a wind generator cannot be controlled on demand. In other words, wind power is not dispatchable. The fluctuating output power of a wind generator affects the voltage profile, losses, reliability and stability of the system. The output power of a wind turbine depends on wind speed which is stochastic in nature. For a given wind speed, the turbine efficiency or performance coefficient () depends on the turbine speed and hence tip-speed ratio (), and blade pitch angle (). The turbine power ( ) can be expressed as:

Where, is the air density, is the blade sweep area and is the wind speed.

In this exercise, a doubly-fed-induction-generator (DFIG) will be studied. To extract the maximum power at different wind speeds, the speed of the wind turbine and hence the generator is required to vary according to the wind speeds. This is done by employing partial size back-to-back power electronic converters (ac-dc-ac). The converters are connected to a common dc capacitor. The rotor side and grid side converters synthesize an ac voltage from a dc voltage source (represented by the dc capacitor). The speed control range of the DFIG depends on the size of the converters used. Usually it is about 30% of the rated power of the generator. Blade pitch angle of the wind turbine is also adjusted to limit the output power (at the rated value) during high wind speeds for protection.

Description:

Fig.1 illustrates the single-line diagram of the wind power plant and the local load considered for this practical.