Transformeless Cascaded H-Bridge Back-to-Back Converter Driving an Dynamic Load

This work proposes a multilevel converter, working as a Solid State Transformer without any magnet transformer, based on cascade H-bridges (CHB) cells in back-to-back (B2B) topology to boost the grid voltage and drive a medium voltage three-phase induction motor. A field-oriented control (FOC) is used with an inner loop feedback flux to generate the motor current references along with a current predicted control (PCC). The B2B configuration is used to achieve all converter four quadrants, so a converter forbidden states map is used to avoid short-circuits, inherent of the CHB-B2B topology. The simulation results showed that the converter could recover 20.6% of active power to the grid and regulate the DC link with a maximum voltage deviation of 6.25%. Also, the inner loop flux significantly improved the field orientation and the maximum rotor speed deviation was 2.0%.