A Unified Arm Module-Based Average Value Model for Modular Multilevel Converter

Abstract

Modeling modular multilevel converter (MMC) for electromagnetic transients is challenging due to the massive number of switching devices. The fast and simultaneous switching events lead to high computational burden as the number of submodules in the MMC increases. Average value models (AVMs) can increase simulation speed by representing converter dynamics using decoupled AC-DC equivalent circuits. However, it is challenging for the state-of-the-art AVMs to represent the blocking operations of the MMC with the decoupled AC-DC equivalent circuits. Blocking modules with additional ideal switches are introduced to the AVMs to emulate the blocking behaviors of the MMC. However, the use of ideal switches bring additional modeling challenges, such as numerical oscillation due to current discontinuity and complicated circuit structures. This paper proposes a new AVM to deliver accurate simulation results with fast simulation speed. Moreover, based on a unified arm module representation, the proposed model can represent the MMCs with different submodule types with the identical circuit structure. The proposed model is validated using test systems based on a two-terminal HVDC system and 11-terminal CIGRE DC grid. It is shown that the proposed AVM provides faster simulation speed compared to the detailed equivalent model and better simulation accuracy than the state-of-the-art AVMs.

Keywords

• Average value model
• blocking module
• detailed equivalent model
• DC pole-to-pole fault
• electromagnetic transients
• HVDC converter