Secondary Control for a D-STATCOM DC-Link Voltage Under Capacitance Degradation

Degradation of the dc-link capacitance due to aging, cell failure, and fuse failure has a negative impact on the ac-side current THD of a distribution static compensator (D-STATCOM) and power quality. These variations noticeably increase the modulation index and dc-link voltage ripple leading to growing the ac-side current THD of the D-STATCOM. To solve this problem, this article proposes a modification mechanism as a secondary control layer added to the common control structure, nested control loops. This upper-hand layer regulates dc-link voltage set-point based on modulation index magnitude to remain the current THD in the standard range indirectly. This method works in steady-state modes and does not change the primary controllers. Simulation and experimental results show that this mechanism properly controls the device and regulates the THD and improve power quality in the network under dc-link capacitance variations.