Generalized Equivalent Circuit Model for MMC-HVDC Simulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing models for large-scale Modular Multilevel Converters (MMCs) are inefficient due to the complexity of detailed switching models, making it time-consuming to simulate dynamic performance, faults, and stability in high-voltage direct current systems, and they only consider limited submodule configurations.
Innovation Solution
A generalized equivalent circuit model (ECM) is developed to simulate MMCs based on various submodule circuits and arm configurations under different operating conditions, including startup, normal, and fault conditions, which can be further optimized with a reduced-order ECM by neglecting individual capacitor voltage dynamics and considering average capacitor voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detailed switching model (DSM) is used to model MMCs, then modeling precision is improved, but simulation time increases significantly making it infeasible for large-scale systems
Solution Approach 1:
The detailed switching model is segmented into equivalent circuit blocks representing different operational states (inserted, bypassed, blocked). Each submodule is represented by simplified equivalent circuits with switching functions that capture essential behavior without detailed semiconductor switch modeling, reducing computational complexity while maintaining accuracy.
Solution Approach 2:
Instead of modeling each individual semiconductor switch, the patent creates equivalent circuit copies that replicate the electrical behavior of submodules. The equivalent circuit model copies the essential switching characteristics and voltage-current relationships without requiring detailed switch-level representations, significantly reducing simulation burden.
2Device complexity
If existing MMC models considering only HB, FB, and UFB SM configurations are used, then model simplicity is maintained, but adaptability to various SM configurations is limited
Solution Approach 1:
The equivalent circuit model is designed with universal switching functions and circuit blocks that can represent multiple submodule configurations (HB, FB, UFB, CD, 3LCC, 5LCC) within a single unified framework. The same basic equivalent circuit structure adapts to different SM types through configuration-specific parameter settings and switching function definitions, eliminating the need for separate models for each topology.
Solution Approach 2:
The model incorporates dynamic switching functions that can adapt the equivalent circuit configuration in real-time based on the operating mode and submodule type. The switching states and circuit connections are dynamically adjusted to match the specific SM configuration being simulated, allowing the model to transition between different operational modes and accommodate various submodule designs.
3Measurement precision
If full detailed switching model is used to investigate internal dynamics and control strategies, then analysis accuracy is improved, but computational efficiency deteriorates
Solution Approach 1:
The patent extracts the essential dynamic characteristics needed for control strategy investigation from the detailed switching model and incorporates them into the equivalent circuit representation. By taking out only the critical elements (capacitor voltage dynamics, arm current relationships, switching functions) and eliminating unnecessary detailed switch-level information, the model maintains analytical accuracy for control studies while achieving computational efficiency.
Data Source
AI summary
A method to simulate a circuit includes receiving at least one circuit requirement and at least one Modular Multilevel Converter (MMC) parameter; determining an operating mode and switching states of an arm circuit; determining each capacitor current based on the switching states and an arm current; determining capacitor voltage and arm voltage; and generating an equivalent circuit model to simulate MMC-based HVDC systems and DC grids in a hybrid AC and DC power system.