Software Phase Locked Loop technique for grid-connected wind energy conversion systems

Accurate and fast detection for phase angle of the generated voltage is important in parallel grid- connected wind energy conversion systems (WECSs) utilizing converter-inverter unites. Software Phase Locked Loop (SPLL) technique is presented here for precisely detecting the phase angle during presence of the 5th and 7th harmonics. A second-order loop filter design is proposed here as a good trade-off of the filter performance and system stability. Also, this proposed technique is studied under frequency change and generated voltage unbalance conditions. The developed technique is also implemented in a laboratory setup which includes two synchronous generators (SGs: 250 W, 2.2 kW) each driven by a variable speed prime mover (VSPM) to emulate a wind turbine behavior, two 3-phase PWM based converter-inverter systems, 3-phase line inductors connected between wind generators and converters, and a digital signal processor (DSP TMS320F240). The experimental results confirm the validity of the proposed technique for parallel integrated WECSs.