A Magnetic Linked Multiport Fractional Converter for Application to Variable Speed Wind Power Generating Systems

A magnetic linked multiport fractional converter (MLMFC) is proposed in this article for application to doubly fed induction generator-based variable speed wind power generating systems. With the proposed MLMFC topology, no back-to-back converter and heavy step-up line-frequency transformer are needed.Moreover, the proposed MLMFC ensures isolation between the rotor-side and grid-side of the system. An improved current sensorless dual-loop individual voltage balance controller (DIVBC) is proposed at the grid-side for individual dc-link voltage balancing for the MLMFC with an interstage controller decoupling technique. The proposed DIVBC shows improved dc-link voltage tracking and dc-link disturbance rejection capabilities. Moreover, an improved current sensorless dual-loop proportional-integral resonant voltage controller (DPIRVC) is proposed at the rotor-side for the strict regulation of the dc-link voltage, the suppression of the dc-link voltage ripples, and the achievement of low controller sensitivity to the load disturbances. Hence, with the combination of the proposed DIVBC with the DPIRVC, the controller architecture requires a low dc-link capacitance without the need to utilize any dc-link current sensors to feedforward any disturbances to the controller. Moreover, the proposed controller architecture shows high stability and robustness under capacitance mismatches, load disturbances, voltage sag and swell, grid fault, and different wind speeds. The superior performance of the proposed control strategy is demonstrated through simulation and laboratory experiments.