A Systematic Controller-Design Approach for Neutral-Point-Clamped Three-Level Inverters

This paper proposes a simple linear feedback-based control technique that ensures zero-neutral-point (NP) potential in three-level voltage-source inverters. The technique works even under dynamic load conditions and enables the decoupled control of the direct and in-quadrature load currents. The technique is based on the relative-gain-array (RGA) approach, which has been successfully used in the control of chemical-engineering processes. The resulting scheme allows the use of outer control loops to set the direct and in-quadrature load currents as required for the specific application (e.g., adjustable speed drives). Experimental results prove the theoretical considerations and show the simplicity of the proposed control scheme.