Active Control of FC-Based A-NPC Inverters Using HIL Platform

Abstract

This thesis presents the development and validation of active voltage-balancing control for flying-capacitor-based active-neutral-point-clamped (A-NPC) multilevel inverters. The work focuses on the analysis of lower-level A-NPC and flying-capacitor-multicell A-NPC structures and the development of high-level nine-level and eleven-level FCM-based A-NPC inverter configurations. These converter structures are designed to synthesize high-quality multilevel output-voltage waveforms while maintaining balanced flying-capacitor voltages. A logic-equation-based control method is developed to regulate the flying-capacitor voltages without using optimization or large switching-state lookup tables. The proposed method uses the output current direction, capacitor-voltage status, normalized voltage error, and priority-selection variables to determine the required charging or discharging action. Based on these logic variables, explicit switching equations are derived to select the proper redundant switching state and generate the gate signals. The proposed control approach is first applied to three-level, five-level, and seven-level A-NPC-based structures to establish the operating principles of multilevel voltage generation and active capacitor-voltage balancing. The method is then extended to the proposed nine-level and eleven-level FCM-based A-NPC inverter structures. Simulation results verify steady-state operation, harmonic performance, flying-capacitor voltage regulation, higher-frequency operation, modulation-index variation, three-phase voltage generation, and semiconductor thermal behavior. HIL validation is also performed for the lower-level and nine-level structures to confirm real-time operation of the proposed control logic. The results demonstrate that the proposed logic-equation-based control method can generate the required multilevel output voltage while maintaining flying-capacitor voltage balance. The thesis shows that the proposed high-level FCM-based A-NPC inverters provide improved voltage resolution and effective active balancing using a direct switching strategy.