Abstract
Grid faults are common in power systems and can have a severe impact on the operation of the converters in the system. In this paper, the operation of a Modular Multilevel Converter (MMC)-based Static Synchronous Compensators (STATCOM) is investigated during grid faults. The study focuses on the challenging internal control of the converter to allow the independent control of the energy levels of each arm, with the goal to maintain internal balancing of the MMC during contingencies. Extensive experimental results highlight the need for a sophisticated internal control. Moreover, the experimental analysis verifies that, by using the proposed control structure, the MMC can effectively ride through a fault on the AC side without tripping, while injecting the necessary positive and negative sequence reactive current levels according to the most recent grid codes.
Highlights
Static Synchronous Compensators (STATCOMs) are used in applications where fast dynamic reactive current injection is needed
This study focuses on the proof-of-concept of the control method using extensive experimental results of the Multilevel Modular Converter (MMC) operation for different cases of AC contingencies, which are considered crucial in such studies, since simulation studies are based on average models, neglecting the non-linear effects of the modulation and the relative delays of the closed loop systems
In the first case scenario, an asymmetrical voltage sag occurs at the AC-side of the MMC STATCOM
Summary
Static Synchronous Compensators (STATCOMs) are used in applications where fast dynamic reactive current injection is needed. The main contribution of the paper is the investigation, implementation and verification of a simple control method, solely based on PI controllers, for internal balancing of an MMC-STATCOM under unbalanced grid conditions, while at the same time Low-Voltage Ride-Through (LVRT) is provided according to the most recent grid codes [34]. For different cases of AC contingencies, which are considered crucial in such studies, since simulation studies are based on average models, neglecting the non-linear effects of the modulation and the relative delays of the closed loop systems For this purpose, a DS-MMC STATCOM laboratory set-up was developed.
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