Developed AC/DC/AC Converter Structure Based on Shunt Active Filter and Advanced Modulation Approach for Asymmetrical Cascade H-Bridge Multilevel Inverters

Abstract

This paper presents a free-harmonic AC/DC/AC converter structure using a novel modulation approach for Asymmetrical Cascade H-Bridge Multi-Level Inverter (ACHB-MLI) and, conventional rectifiers combined with a shunt active filter, for grid integration. The novel approach SMT-SHE combines two modulation techniques: the Staircase Modulation Technique (SMT) and the Selective Harmonics Elimination (SHE). SMT-SHE approach achieves a sinusoidal-like output stepping voltage with variable output voltage amplitude and free of wide band or/and specific harmonics to fulfill the sensitive loads specifications; by determining the appropriate SHE switching angles. The precalculated switching angles are optimized to minimize the number of H-bridge modules and lower the DC capacitors rating. Furthermore, a restriction on the switching angles is proposed to prevent the appearance of undesired harmonics (zeros, even) and consequently overcome the limitation of the SHE algorithm applicability. Finally, a real case study in textile factory is conducted, using real measurements provided by power quality analyzer measuring devices, to validate the proposed AC/DC/AC converter supplying a sensitive load of 50 kVA, given by an asynchronous motor drive.

Shunt Active Power Filters in Three-Phase, Three-Wire Systems: A Topical Review

“…In the case of medium/high voltage and large power applications, the multilevel topologies of SAPF have been proven to be more advantageous than the classic topology with two levels in terms of switching losses, power switch voltage stress, and AC current waveform [5,[20][21][22][23][24][25][134][135][136][137][138][139][140]. Because the higher the inverter level number, the higher the number of power semiconductor devices and DC capacitors, and the complexity of the control system is increased (including the need for specific DC voltage balancing techniques), in most SAPF applications, multilevel inverters with more than three levels are used less often.…”

“…The most used three-phase, three-wire, three-level topology of inverters used for SAPFs is neutral-point diode clamped (NPC) (Figure 3a) [5,[20][21][22][23][24][25][134][135][136]. Other topologies are flying capacitor (FC) (Figure 3b) [20,137,138] and cascaded H-bridge (CHB) (Figure 3c) [20,139,140]. The three-level NPC-based structure is robust and requires only two DC-link capacitors, so that the voltage imbalance problems are the least and the physical size is smaller.…”