Abstract
In recent years, a special attention is paid to grid connected multilevel converters. These converters have specific use in industry in a high power, medium-voltage and high-voltage applications. This paper presents new control algorithm for single-phase AC/DC modular multilevel converter with target application as a traction converter connected directly to trolley wire. The proposed control strategy presents resonant controllers for converter current control with fundamental frequency adaptation. The fundamental frequency estimation and voltage synchronization is based on Second Order General Integrator Phase Locked Loop (SOGI-PLL). Furthermore, this paper presents robust voltage balancing technique for multilevel converter based on energy calculation of DC-link capacitances. It provides voltage balancing of multilevel converter cells with unbalanced load. The resulting control algorithm has low total harmonic distortion of converter trolley current even under unbalanced load condition. The algorithm was experimentally verified on the low voltage laboratory prototype with 3 H-bridge cells.DOI: http://dx.doi.org/10.5755/j01.eie.24.6.22282
Highlights
The objective of this research is to develop a modular multilevel converter used as AC/DC converter for traction application
This paper introduces voltage balancing method based on direct energy calculation
The switching frequency of our laboratory prototype is 1 kHz, which leads to 6 kHz dominant current frequency component of 7-levels cascaded h-bridge (CHB)
Summary
The objective of this research is to develop a modular multilevel converter used as AC/DC converter for traction application. The CHB converters used as a grid connected converters are presented in [2]–[10] This topology is favourite choice in many other industrial applications such as power electronics transformers (PET) [3], [5], [6], [10] or voltage-source inverters [7]. The paper presents novel algorithm for CHB rectifier control focused on system robustness with voltage amplitude and frequency adaptation on AC side and voltage balancing method compensating load imbalance on DC sides. The hysteresis control is simple and robust it leads to various switching frequency and wide noise bandwidth For this reason, PWM techniques dominate in high power applications. This energy is calculated for each HB during one period (0.02 s)
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