A Reconstructed Nearest Level Modulation Method With ABC Coordinate-Based Deadbeat Predictive Control for the Four-Level Single Flying Capacitor Converter

This article presents a new modulation method based on nearest level modulation (NLM) and phase voltage level reconstruction for the four-level single flying capacitor (4L-SFC) converter. The reconstruction procedure addresses the voltage balancing issues of the 4L-SFC converter and performs the per-phase modification of the phase voltages. In the proposed reconstructed NLM (R-NLM) method, the modulation procedure is carried out in the abc reference frame to eliminate the complexities associated with the space vector modulation (SVM). It is also compatible with the per-phase implementation of the reconstruction, making the whole process more straightforward. The required computations in the NLM-based reconstruction are also reduced when compared to the SVM-based reconstruction technique. The current control task is carried out using deadbeat predictive control (DBPC) by defining the system model in the abc coordinate. Also, a new approach for estimating the common-mode voltage (CMV) value, required in the abc frame-based system model, is presented. Simulation results demonstrate that the proposed R-NLM simplifies the modulator while retaining the performance of the SVM-based modulation technique for the 4L-SFC converter. The R-NLM alongside DBPC in the abc coordinate is implemented on a laboratory scale setup of the 4L-SFC converter to validate the feasibility of the proposed modulation scheme.

I. Introduction

Multilevel voltage source converters have emerged as promising solutions in a wide variety of low-, mid-, and high-power applications [1], [2], [3], [4]. When compared to a two-level voltage source converter, these converters offer many benefits, such as lower distortion of voltage waveforms, lower voltage stress on switching devices, lower , and lower switching losses. These advantages come with some challenges, such as a complicated structure and control requirements [4]. Furthermore, the high component count is always a barrier for these converters. In general, capacitor-based multilevel converters with a high number of voltage levels need many capacitors with the need to regulate their voltages at the desired levels, also known as capacitor voltage balancing [5], [6], [7]. The high number of capacitors always adds to the control complexity of these converters [4]. Consequently, some research has been focused on reducing the number of capacitors employed in the structure and thus reducing the overall cost and size. In addition, the development of an appropriate control and modulation scheme has always been a concern [5], [6], [7], [8], [9], [10], [11].