A Delta Connected Hybrid STATCOM and Dc Capacitor Voltage Balance Technique Using Zero-Sequence Current

Abstract

The parallel hybrid converter (PHC) is advantageous over the modular multilevel converter (MMC) in terms of energy storage requirement, number of switching devices, capacitors and switching losses. However, the PHC cannot be employed for static compensation (STATCOM) applications, owing to its nature of operation at a fixed modulation index (MI). The PHC utilizes harmonic injection methods (HIMs) to regulate its MI, within narrow limits. These harmonic voltages tend to be unequal, during unbalanced grid conditions (UGCs), and therefore enter the grid and distort it further. This paper proposes a new delta hybrid STATCOM (DH-SC) which inherits the advans power with the grid and hence the capacitor voltages belonging to different CLs divert from its reference value. However, the capacitor voltages get restored to its original value with the injection of unequal third harmonic voltages as mentioned above. Nonetheless, these unequal harmonic voltages enter into the grid and further degrade its power quality. This paper proposes a new delta hybrid STATCOM (DH-SC), which is capable of operating at any MI without requiring any THIMs, both during balanced and unbalanced grid conditions. The proposed DH-SC converter also inherits the advantages of PHC over MMC such as lower energy storage requirement, lesser number of capacitors and lesser switching loss.