To research control characteristics of permanent magnet synchronous generator(PMSG) for direct-driven variable-speed constant-frequency(VSCF) wind energy conversion system(WECS),the principle of back-to-back converters was discussed,then the work principles of encoder and sensorless control were analyzed.

Based on analysis to the principle of back-to-back converter for direct-driven variable speed constout frequency(VSCF) WECS,phase lock loop(PLL) based sensorless control strategy was adopted to determine the speed and phase angle of PMSG,and its work principle and realization method are analyzed in detail.

Throughsystem study, the interconnection scheme will start at AC links and finally change to DC back to back links.

Equipment layout and connection design inside valve hall is the key to back-to-back converter station engineering design,and is also very challenging.

The AC system at the China side of China-Russia back-to-back converter station located at China-Russia border is weak, to solve this problem a static var compensator (SVC) will be installed to match up with the operation of HVDC system and enhance transient stability of AC system.

Based on the design summary of Lingbao back-to-back converter station which connects northwest China power network and central China power network,this article analyzes the characteristic of station design for HVDC back-to-back converter stations.