Gradient-Based Predictive Pulse Pattern Control with Active Neutral Point Balancing for Three-Level Inverter Medium-Voltage Drives

This paper presents a control method for three-level neutral point clamped (NPC) inverter medium-voltage (MV) drives that addresses the stator current control problem and balancing of the neutral point (NP) potential in a single control loop. To do so, a model predictive control (MPC) algorithm, designed as a multiple-input multiple-output (MIMO) controller, manipulates optimized pulse patterns (OPPs) in real time. As a result, minimal current harmonic distortions are produced, while the NP potential is kept balanced both during steady state and transients. The presented results demonstrate the effectiveness of the proposed control strategy for three-level NPC inverter MV variable speed drive systems.

I. Introduction

Multilevel converters are widely used in industrial applications to drive medium-voltage (MV) machines. To operate MV drives with high efficiency, operation at very low switching frequencies is required to minimize the switching power losses [1]. However, such low switching frequencies can lead to high current distortions, and thus adverse effects, such as increased losses in the machine. To address this issue, optimized pulse patterns (OPPs) can be employed as they are computed to produce the theoretical minimum current distortions [2].