Current Sensorless Control Algorithm for Single-Phase Three-Level NPC Inverter

Abstract

Current measurement becomes challenging task in power converters operating at high switching frequencies, moreover traditional control system requires two control loops – first (slow) regulates DC-link voltage, second (fast) controls the shape of current, that all together results in complicated transfer function and long transition periods. The current sensorless control allows neglecting mentioned problems. This research delivers solution of CSC implementation in single-phase three-level neutral point clamped inverter for the first time. Mathematical equations were defined for inductor current peaks and transistor conduction time during DCM and CCM, as well as, major problem of current fitting between different voltage levels (consequently with different current peak-to-peak values) was solved, providing two solutions – pre-fitting and post-fitting trajectories. The verification of our theoretical assumptions and analytical equations were confirmed by the simulation analysis. Challenges of real experiments are discussed in the conclusions.