Modular Multilevel Converter Submodule Arc Protection
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Solution Overview
Problem
Modular multilevel converters face challenges in efficiently detecting and handling defective sub-modules, particularly in maintaining system operation and preventing damage from arcs during communication failures or bypass switch malfunctions.
Innovation Solution
The procedure involves generating a converter-internal circular current if necessary, to ensure a minimal current flow through submodules, facilitating faster detection of bypass switch failures and reducing the risk of arcs. This is achieved by determining if the arm flow is below a threshold, and if so, generating an internal circular current to load the electrical energy storage of the defective submodule.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a minimal current flow is maintained through submodules to enable fast detection of bypass switch failures, then the detection speed and safety improve, but the energy losses increase during low power or idle conditions
Solution Approach 1:
The system dynamically adjusts the current flow through submodules based on operational state. During normal operation, minimal current maintains detection capability. During low power or idle conditions, the system reduces or suspends this current to minimize energy losses, while still maintaining the ability to detect bypass switch failures when needed.
Solution Approach 2:
The system changes the current parameter dynamically - maintaining a minimal threshold current during active operation for fast failure detection, but reducing this current parameter during low power or idle conditions to reduce energy consumption. This parameter adjustment resolves the contradiction between reliable detection and energy efficiency.
2Loss of energy
If the system waits for natural current flow to charge the electrical energy storage of a defective submodule, then energy efficiency is maintained, but the detection of bypass switch failures is delayed increasing arc risk
Solution Approach 1:
The system performs preliminary action by generating an internal circulating current that specifically flows through defective submodules to charge their electrical energy storage devices. This proactive charging mechanism ensures that bypass switch failures are detected quickly without waiting for natural current flow, thus reducing detection time while maintaining overall energy efficiency through targeted current application.
Solution Approach 2:
An internal circulating current is introduced as an intermediary mechanism to charge the electrical energy storage of defective submodules. This intermediate current path enables faster charging and detection without requiring full system current flow, thus reducing detection time while minimizing impact on overall energy efficiency.
3Loss of time
If an internal circulating current is generated to charge defective submodules, then the detection speed improves, but the device complexity increases
Solution Approach 1:
The control system is designed with multi-functionality to handle both normal operation and defective submodule conditions. The same control device that manages overall converter operation also generates and controls the internal circulating current for charging defective submodules. This universal approach improves detection speed without requiring separate dedicated hardware, thus minimizing the increase in device complexity.
Solution Approach 2:
The system uses its own existing control infrastructure to generate and manage the internal circulating current. The control device serves multiple purposes - normal converter control and defective submodule charging - making the system self-sufficient. This self-service approach reduces the need for additional complex external systems while improving detection speed.
Data Source
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AI summary
The invention relates to a method for operating a modular multilevel converter (10) having a plurality of sub-modules (1, 2, 3, 4, 5, 6), each of which has at least two electronic switching elements (12), an electric energy store (14), two sub-module connections (11), a bypass switch (15) for bridging the sub-module (1, 2, 3, 4, 5, 6) thereof in the modular multilevel converter (10), and a communication element (20) for communication with a communication apparatus (30) of the modular multilevel converter (10), the method comprising the steps: (a) identifying that the plurality of sub-modules (1, 2, 3, 4, 5, 6) have a sub-module (1, 2, 3, 4, 5, 6) which is defective so that the communication element (20) in the defective sub-module (1, 2, 3, 4, 5, 6) does not communicate with the communication apparatus (30), (b) determining whether a current arm current resulting from an operating point of the modular multilevel converter (10) is below a predetermined threshold value, and (c) generating or amplifying a converter-internal circular current in the modular multilevel converter (10) comprising the defective sub-module (1, 2, 3, 4, 5, 6) if the arm current resulting from the operating point of the modular multilevel converter (10) is below the predetermined threshold value. The invention also relates to a modular multilevel converter (10).