Performance Of Multilevel Converter Research Articles

Selective Harmonic Elimination Technique Improvement for Cascaded H-Bridge Multilevel Converters Under DC Sources Uncertainty

The performance of multilevel converters (MLCs) is at the risk of uncertainty of DC sources. This issue has a more negative effect on three-phase cascaded H-bridge MLCs (CHB-MLCs) due to more isolated DC sources. DC voltage variation can take place in all phases, but in this paper, the effect of DC voltage variation of one phase on line voltages is considered. This problem can lead to unbalanced line voltages and a lack of third harmonic elimination in a spontaneous way. Therefore, these problems cause to modify the formulation of quarter-wave symmetrical selective harmonic elimination (SHE) for three-phase CHB-MLCs so that the line voltages become resistant to DC voltage variations as well as mitigating third harmonic. To keep line voltages amplitude fixed under variation of DC voltages, it is necessary to take advantage of non-identical modulation indices to exploit the maximum capacity of DC voltages. Furthermore, regarding unequal DC voltages that can appear in numerous states in a phase, a new method based on the average of DC voltages (ADCV) per phase is employed in the formulation of SHE to reduce these states. Finally, both simulation and experimental results are presented to validate the performance of the proposed method.

An interleaved multilevel converter for onboard EV charging application

ABSTRACT This paper proposes an interleaved multilevel converter (MLC)-based charger with power rating 2.8 kW to charge on-board battery of electric vehicle (EV). It comprises two stages: (1) an interleaved multilevel ac–dc converter; and (2) an LLC-resonant dc–dc converter. The interleaved approach efficiently maintains the optimum power level. The switching scheme implemented for MLC maintains the source current sinusoidal, supports unity power factor (UPF) and has the capability to balance the capacitor voltage. The MLC maintains UPF and balances capacitor voltage without any auxiliary circuit. In addition, MLC provides lower voltage stress and reduced total harmonic distortion (THD), therefore, making it a better choice for ac–dc conversion stage in battery charging application. The dc–dc converter furnishes regulated and wide output voltage range for on-board charging system. The principle of operation, modulation technique and control strategy for both the converters are analysed. Following theoretical analysis, laboratory experiments were conducted to validate the implemented approach. The results signify that for output voltage range of 24−72 V, UPF is maintained at input, lower stress across switches and capacitor voltage is balanced. The performance of MLC is satisfactory as it attains a peak efficiency of 97% with THD of 2.07%.