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

Abstract

The current measurement is becoming a 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 (CSC) allows neglecting the mentioned problems. This research for the first time presents the solution of CSC implementation in single-phase three-level neutral point clamped inverter. Mathematical equations were defined for inductor current peaks and transistor conduction time during discontinuous and continuous conduction modes, 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 was confirmed by the simulation analysis. Challenges of real experiments are discussed in the conclusion.

Bidirectional single-loop current sensorless control applied to NPC multi-level converter considering conduction losses

“…This type of control utilises only one control loop with feedback from the output capacitor voltage and does not use any current feedback signal as it is assumed that inductor's volt-second balance is perfectly calculated and inductor's current follows the reference signal (see Figure 1 (c)). Since that time the CSC has been applied to multiple type of PFC topologies: single switch PFC (diode bridge and boost converter) [38,39], interleaved [40,41], bridgeless [42,43], half-bridge [44][45][46], full-bridge [47,48] and also neutral-point clamped multi-level converter (NPC MLC) [49,50]. Several recently published papers have been devoted to different type of three-phase converter topologies operated under CSC [51][52][53] that makes evidence of CSC use in high power applications.…”

Verification of current sensorless control for single-phase NPC multilevel inverter

“…There was also attempt to use CSC with NPC multilevel inverter [20], however, despite the fact that it discusses sensorless control strategy, simple sinusoidal PWM modulation is utilized, giving no sense on sensorless control. The very basic information on problems of applying CSC to multilevel NPC converter is discussed in [21]. S11 AC S13 L1 S12 S14 …”

Current sensorless control for half‐bridge based AC/DC PFC converter with consideration of conduction losses

“…The interleaved PFC with phase-shedding function has also been evaluated in [37]. Several other approaches were dedicated to implementation of CSC with bridgeless [38], half-bridge [21,39], and even multilevel type of converters [34,40]. The last one is challenging because of problem of proper volt-second balance during transition between different voltage levels, where it was proposed to use pre-fitting and post-fitting current matching trajectories.…”