A Modified Nearest Level Control Scheme for Improved Submodule Current Sharing in a CHB Converter with Integrated EDLCs

• Published in: Energies (Basel) Vol. 18; no. 7; p. 1697
• Main Authors: Döhlen, Viktor, Bertilsson, Kent
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.04.2025
• Subjects: Algorithms; Capacitors; CHB; direct integration; EDLC; Electric current converters; Electric power; Electricity generation; Energy storage; Integrated circuits; Investigations; nearest level control; Semiconductor chips; vertical balancing
• ISSN: 1996-1073; 1996-1073
• DOI: 10.3390/en18071697

This study investigates a Cascaded H-Bridge converter with Electric Double-Layer Capacitors as integrated energy storage components. As the DC-link voltages are variable, the modulation index and number of submodules contributing to the active power delivery vary according to state of charge. The nearest level control algorithm for this application is studied, and expressions for the duty cycle of conventional Nearest Level Modulation are derived. A modification of the sort and select algorithm to determine which submodule is to be inserted and bypassed when using the Nearest Level Control algorithm is proposed to distribute the activation time and the experienced RMS current of the submodules. Expressions for the duty cycle of each inserted submodule for the proposed algorithm is presented and compared to the conventional. Simulation experiments of current sharing between submodules under active power delivery for the conventional and proposed Nearest Level Control is conducted for an 11- level, 41-level and 61-level converter. Simulation experiments show a reduction in RMS current for the submodule experiencing the highest thermal stress. Over the course of power delivery and increasing modulation index, the peak RMS current increase for the conventional nearest level modulation while it is kept constant for the proposed modulation scheme.