Zero-Sequence Voltage Injection Method for DC Capacitor Voltage Balancing of Wye-Connected CHB Converter under Unbalanced Grid and Load Conditions

Jae-Myeong Kim, Geum-Seop Song and Jae-Jung Jung
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Jae-Myeong Kim: School of Electronic and Electrical Engineering, IT College, Kyungpook National University, Daegu 41566, Republic of Korea
Geum-Seop Song: School of Electronic and Electrical Engineering, IT College, Kyungpook National University, Daegu 41566, Republic of Korea
Jae-Jung Jung: School of Electronic and Electrical Engineering, IT College, Kyungpook National University, Daegu 41566, Republic of Korea

Energies, 2021, vol. 14, issue 4, 1-18

Abstract: Leg capacitor energy balancing control is one of the crucial issues for stable operation of a cascaded H-bridge (CHB) converter. Because this topology inherently consists of numerous submodule cells with DC capacitors, the cell voltages and leg capacitor energy instantaneously fluctuate depending on operation sequence of the CHB converter. In general, a wye-connected CHB-converter-based static synchronous compensator (STATCOM) utilizes a zero-sequence voltage component for leg capacitor energy balancing. In this paper, to improve the dynamics of leg energy balancing control, a feedforward calculation method of the zero-sequence voltage injection is proposed. The feedforward term can be instantaneously calculated by using the information from the measured leg voltages and leg currents, and the method ensures successful regulation of the leg energy balance even under unbalanced grid and load conditions. Moreover, the verification of the proposed method is supported by the mathematical vector theorems. A 50MVA full-scale wye-connected CHB–STATCOM system simulation was performed to verify the proposed feedforward calculation method considering unbalanced grid as well as unbalanced load conditions.

Keywords: cascaded H-Bridge (CHB) converter; feedforward calculation; grid imbalance; leg energy balancing; load imbalance; static synchronous compensator (STATCOM); zero-sequence voltage injection (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (4)

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