Zero-sequence voltage injection for DC capacitor voltage balancing control of the star-connected cascaded H-bridge PWM converter under unbalanced grid

2014 ◽  
Author(s):  
Chia-Tse Lee ◽  
Hsin-Chih Chen ◽  
Ching-Wei Wang ◽  
Ping-Heng Wu ◽  
Ching-Hsiang Yang ◽  
...  
Keyword(s):  
Pwm Converter ◽  
Voltage Balancing ◽  
Capacitor Voltage ◽  
Zero Sequence ◽  
Zero Sequence Voltage ◽  
Balancing Control ◽  
Unbalanced Grid

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

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1019
Author(s):  
Jae-Myeong Kim ◽  
Geum-Seop Song ◽  
Jae-Jung Jung
Keyword(s):  
Calculation Method ◽  
Stable Operation ◽  
Energy Balancing ◽  
Static Synchronous Compensator ◽  
Unbalanced Load ◽  
Zero Sequence ◽  
Zero Sequence Voltage ◽  
Balancing Control ◽  
Unbalanced Grid ◽  
Load Conditions

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.

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