Phase-Disposition PWM Based Active Voltage Control of Seven-Level Nested Neutral-Point-Piloted (NNPP) Inverters

This paper introduces logic-equations for active voltage balancing of seven-level nested neutral-point-piloted (NNPP) inverters. It measures the load current and voltage of floating-capacitors (FCs). These instantaneous measurements are then translated into logic-variables on basis of their reference values. Next, the interpreted logic-variables are employed in a set of logic-equations that are specifically derived for the 7-level NNPP inverters. These equations aim to actively balance the FC voltages at their target operating levels and to generate the reference voltage-level according to the adopted PWM strategy. As an outstanding advantage, the proposed logic-equations-based active-voltage balancing method eliminates all the complicated and time-consuming computations that are necessary in the conventional active balancing approaches since it is not utilizing or optimizing any cost/energy functions. The experimental results obtained from a 7-level prototype of the NNPP converter are provided to verify the logic-equations and active control method.