A sub-module capacitor voltage balancing scheme for the Alternate Arm Converter (AAC)

A per-phase sub-module capacitor voltage balancing scheme for the Alternate Arm Converter (AAC) is proposed. Leg balancing regulates the sum of sub-module capacitor voltages in a leg to its set-point. Arm balancing regulates each sub-module capacitor voltage to the nominal sub-module capacitor voltage. Additional converter control requirements and the modulation scheme are also discussed. The control and modulation scheme has been verified by simulation. The leg balancing control loop was designed to be critically damped to primarily limit oscillations in the output variable caused by changes in AC-side power demands; the simulation results indicated this specification was met.