Virtual Vector Optimal Selection Strategy for NPC Three‐Level Grid‐Tied Converter with Finite Control Set Model Predictive Control

Abstract

Virtual vector is applied in neutral-point-clamped (NPC) three-level converter finite control set model predictive control (FCS-MPC) strategy due to its good performance of less current ripples and high power efficiency. However, in the process of adding virtual vectors, some redundant virtual vectors will be selected. Excessive virtual vector will increase the computational burden and affect grid-tied current performance. A virtual vector optimal selection strategy for model predictive control to determine the vectors is proposed. The strategy calculates the fluctuation of grid-tied current through theoretical analysis. Based on the analysis of amplitude fluctuation of grid-tied current, the graphics of coverage angle visualization can be obtained under different virtual vector. The angle of the required virtual vectors is obtained through the graphics of coverage angle visualization. The number of virtual vector can be determined when the error current angle range covers the entire vector graph. The proposed control strategy was compared with the conventional control strategies, including excessive virtual vectors or with no any virtual vector. Experimental results show that the proposed control strategy can significantly reduce THD, grid-tied current error and computational burden.

Improved Sequential Model Predictive Control of Cascaded H‐Bridge Multilevel Converter

“…By using the discrete prediction model (2), the converter current of any future time step can be predicted according to the system state at time step k . In (2), v (k ) denotes the control variable and is determined by the state of each SM of the three phases [26,27]. By controlling the working state of these SMs, different voltage levels can be generated on the ac side (v a , v b , v c ).…”

“…With the rapid development of power electronic technology, power converters have played a more and more critical role in improving the power quality and stability of the utility grid [1,2]. For middle and high-voltage power distribution systems, multilevel power converters can achieve high output voltage and power with low-voltage switching devices [3].…”