On Control of Delta-CHB STATCOM

Static Synchronous Compensators (STATCOMs) are a widespread solution for reactive power compensation and offer advantages such as fast response, smaller footprint, and voltage disturbance support. The Delta-CHB converter is one of the most preferred medium- and high-voltage STATCOM topologies in the industry. However, this topology poses challenges for those researchers who intend to develop new modulation strategies, power loss reduction techniques, capacitance reduction schemes, and fault-tolerant methods due to the relatively complex control structure with several objectives required. Previous publications present control strategies for this topology, but they still lack approaches where the system modeling and the control tuning are performed straightforwardly with enough details and validity. This paper presents the dynamic model of the Delta-CHB STATCOM that allows the employment of well-known and analytical control tuning strategies for all control loops involved. Although the individual control loops are somehow covered in previous publications, this work consolidates key design details into a single reference. It also provides insights regarding the normalization strategy employed and its effects on the circulating current. The proposed modeling dynamic response is compared with the simulation results of a real 90 MVA STATCOM plant. This paper also provides experimental results demonstrating the adopted approach’s effectiveness, which reaches all control objectives (capacitor voltage control, capacitor voltage balancing, circulating current suppression, and reactive power control at the point of common coupling). Furthermore, the normalization strategy reduced the experimental ripple of the circulating current by 29.95%.