Synchronization and Mains Outage Detection for Controlled Grid Connection of the Wind Driven Variable Speed Power Generation System.

Power electronics devices used in power generation systems with electrical machines allow variable speed operation. A high quality output power is delivered to the transmission network. Moreover the power electronics allow stand alone operation in an island power systems, as well as in grid connected systems during the mains outage. This way the variable speed power generation systems are useful even during the network failures. It is a significant advantage especially in distributed generation concept. However, the mains outage detection methods are necessary for controllable disconnection of the generator from the grid. Also reconnection of the generator to the grid requires the prior voltages synchronization, that protects the load from the rapid change of the supply voltage phase. This paper presents a controllable grid connection to stand alone transitions of the doubly fed induction generator. Two complementary methods of the mains outage detection based on the stator voltage amplitude and frequency determination are presented. Moreover, an angle controller is applied for synchronization of the stator and grid voltages, before the reconnection of the generator to the grid. A direct voltage control method used for stand alone operation does not require any information about the rotor angular position or speed.