Steady-state and small-signal models of a three-phase quasi-Z-source AC–DC converter for wind applications

The three-phase quasi-Z-source AC–DC converter possesses many attractive attributes for applications with wide AC input variations, such as variable speed wind generator applications. This is due to its buck–boost capability, high input power factor, low output ripple and low rating of components. Detailed steady-state and small-signal models of the converter are derived using circuit averaging and the synchronous reference frame. From the steady-state model, it is shown that the three-phase quasi-Z-source rectifier (QZSR) has all the advantages of the three-phase Z-source rectifier (ZSR) as well as further advantages such as lower rated capacitors. The small-signal model reveals that the QZSR has non-minimum-phase zeroes in its control-to-output voltage and control-to-inductor L 1 current transfer-function similar to the ZSR. Right-half-plane zeroes tend to limit the maximum control bandwidth and destabilise the wide-bandwidth feedback loop. The key elements in the design of a closed-loop controller, namely, the transfer functions and the block diagram models are derived. Simulations and experimental results are presented to validate the models developed.