FPGA Control of a Single-Phase T-Type NPC Grid Inverter for Low THD and Robust Performance

Abstract

This paper presents an FPGA-based adaptive predictive control scheme for single-phase T-type NPC inverter in applications to microgrids with high efficiency and robust performance. Predictive control is applied for current regulation to achieve fast dynamic response with low total harmonic distortion (THD). Implementation of a grid inverter with minimum inductor will result nonlinear inductance due to saturation effect. This nonlinearity can be tolerated with conventional PI controller with low bandwidth performance, however, oscillations or even instability may occur for predictive control with fast dynamic responses. An adaptive predictive control scheme with on-line inductance identification has been developed to ensure both fast dynamic response and robust stability. The proposed adaptive predictive controller has been realized using a mixed-signal FPGA Smartfusion (R) A2F500 from Microsemi. Experimental verification is carried out with a 3kW single-phase AT-NPC grid inverter. Experimental results show that the proposed control scheme can achieve both fast dynamic responses and high quality current regulation with THD close to its theoretical limits.