DC-Link Capacitors’ Voltage Balance in an HB-NPC Five-Level Grid-Tied Inverter via the Common-Mode Control Component

This article presents a control method to balance, in average, the dc-link capacitor voltages while injecting power to the grid using an h-bridge neutral-point clamped five-level inverter grid tied through an inductor–capacitor–inductor (LCL) filter. The method exploits the structure of a particular model representation of the system comprising a differential-mode (DM) part and a common-mode (CM) part, which turn out to be decoupled from one another. These decoupled representations enormously facilitate the control design as it can be performed as two independent processes as well. The first design process involves the DM model part and focuses on the grid current injection, while the second design process focuses on the balance of the dc-link capacitors voltages and is based on the CM model part. Out of this, two control components are derived, namely DM and CM control components, which are later recombined to form the two control signals, one per inverter branch, required as references in a conventional modulation algorithm to generate the switching sequence. Numerical and experimental results are performed to evaluate the performance of the proposed controller for the h-bridge neutral-point clamped inverter subject to those interconnections.