Sliding-Mode Control for Interleaved Operation of Parallel-Connected Three-Phase Active Front-Ends

A converter system is considered that consists of parallel-connected two-level voltage source converters that share the same ac and dc terminals. A controller design is proposed that, in a first stage, controls the grid currents using hysteresis controllers. To this end, augmented grid currents are introduced, which feature decoupling between the phases. As a consequence, a switching action in one phase does not affect the derivatives of these currents in the other phases. In a second stage, the converter currents are controlled using hysteresis controllers such that a desired current distribution among the parallel converters may be ensured. This implicitly sets the circulating currents. The proposed approach is verified by measurements on an industrial megawatt-scale testbench with ten parallel converters. The results are compared with a benchmark approach, with the proposed approach showing lower semiconductor losses and grid current harmonic distortion.