Current source thyristor inverter and its active compensation system

A grid-commutated thyristor inverter based power electronic interface for a direct-drive modular permanent magnet generator in a variable-speed wind energy conversion system is described. The AC/DC/AC power electronic interface consists mainly of a diode rectifier and a thyristor inverter. The inverter ignition angle can be adjusted continuously to control turbine speed so that the optimal energy capture is achieved. The reactive power and harmonic characteristics of the thyristor converter system have to be compensated to meet the standards for grid connection. An active compensation system is discussed to minimise the harmonic distortion and to provide reactive power control. A simple method of deriving the reference current for the active compensator is proposed on the basis of optimal operation conditions. Several compensation schemes are considered. Experimental results from a laboratory model are presented along with computer simulation results, which are in good agreement.