Current vector control based on average capacitor voltage strategy and hybrid modulation applied to the control of a 7-level PUC three-phase inverter

This paper presents a vector control system for the control of the capacitor voltages of a 7-level Packed-U-Cell (PUC) three-phase inverter. Usually, PUCs in a three-phase system are controlled as isolated systems. As a result, three voltage loop and three load current loops are required to control the capacitor voltage in each PUC. Additionally, conventional approach requires the tracking of sinusoidal references. This paper proposes a different approach. A single voltage loop is designed to control the average voltage of the capacitor. This loop defines the required tf-axis load current, while the required q-axis load current is set to zero. Two current controllers generate the voltage references to get the required dq currents. Those voltages are produced through hybrid modulation (HPWM). As a result, only three control loops are needed to control the capacitor voltages. The proposed approach reduces the computational cost of the PUC controller, makes easier the control tuning, and the current control improves, due to the steady-state dq load current referents are almost constants, which are easier to track than sinusoidal references. Simulation results show that the proposed vector control for a three-phase PUC inverter is accurate and robust against parameter variation.