Figure 3-1 shows a schematic diagram of a typical wind-diesel hybrid system. The main components of a hybrid wind-diesel power generation system are: wind turbine with associated controls, diesel engine; electric generator with power electronic controllers (PEI), loads and bidirectional power electronic converter. Wind Turbine The wind turbine should be able to capture maximum energy via Maximum Power Point Tracking (MPPT) during low wind speed conditions as well as high wind speed conditions. The tip speed ratio must be brought to a particular value to obtain MPPT under low speed conditions. This can be done by regulating the electromagnetic torque of the generator using appropriate power electronic controllers so that the quadrature axis component (the torque producing component) of the current in the three-phase AC generator is appropriately manipulated. During higher wind speed conditions (greater than the rated wind speed for which the turbine is designed), pitch control is activated so that the generator capacity is not exceeded and currents and voltages are within safe limits . During this condition, the generator will operate with constant power control. Diesel Engine/Generator Generators used with diesel engines are three-phase wound-field synchronous generators whose terminal voltage is maintained at rated value by excitation control. The diesel engine governor control mechanism controls the frequency. Normally the generator used in conjunction with wind power is an induction generator (IG) or a PMSG. For night-time operation of a hybrid system a DFIG is used. Self-excited squirrel cage induction generators (SCIG) operating in generation mode only at super-synchronous rotor speeds...... middle of the paper..... .so within safe speed limits. The load side converter is controlled by a chopper and an inverter as discussed above to maintain the voltage across the DC link capacitor at a constant value. DFIG control via current-connected converters The current-connected converter uses thyristorized converters on both the rotor side and the load side for real power control. This configuration is the one shown in fig 3-4. The driving operation is performed at sub-synchronous speed and the generating operation for super-synchronous speed since the voltage can be reversed in both converters, depending on the range of firing angles at which each of them operates. For sub-synchronous speed motor operation, the rotor side will work as a rectifier and the converter on the load side will work as an inverter. This will be opposite in supersynchronous generation mode.