MMC HVDC Redundancy Control Under Submodule Failure
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Solution Overview
Problem
When a submodule breakdown occurs in a modular multilevel converter (MMC) for HVDC and there are no more redundancy submodules available, voltage imbalance leads to system interruption, affecting the electric power system.
Innovation Solution
Adjust the DC link voltage input to each converter arm and lower the output voltage of operational submodules to maintain balanced operation, allowing continuous operation without additional redundancy modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundancy submodules are added to replace broken submodules, then system reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the operating parameters of the MMC system by adjusting the DC link voltage and the output voltage of healthy submodules. When a submodule breakdown occurs and no redundancy is available, the control method modifies voltage parameters to redistribute the voltage burden among remaining submodules, enabling continuous operation without adding physical redundancy components.
2Reliability
If redundancy submodules are added as spares, then fault tolerance is improved, but loss of substance and cost increase
Solution Approach 1:
Instead of adding physical redundancy submodules (which would increase substance loss and cost), the patent uses parameter changes to achieve fault tolerance. The control method adjusts voltage parameters dynamically to compensate for submodule failures, providing fault tolerance through control strategy rather than additional physical components.
3Reliability
If DC link voltage and submodule output voltage are lowered, then voltage imbalance is prevented and system continuity is maintained, but power output decreases
Solution Approach 1:
The patent applies partial action by lowering the DC link voltage and submodule output voltages only to the extent necessary to maintain voltage balance and prevent system interruption. This partial reduction in voltage allows the system to continue operating at reduced capacity rather than shutting down completely, representing a trade-off where some power output is sacrificed to maintain system continuity.
4Device complexity
If the MMC operates without redundancy submodules, then device complexity is reduced, but reliability deteriorates when additional breakdowns occur
Solution Approach 1:
The patent uses parameter changes to compensate for the lack of physical redundancy. By dynamically adjusting the DC link voltage and submodule output voltages, the control method creates a virtual redundancy effect that maintains system reliability without adding physical components, thus resolving the contradiction between device complexity and reliability.
Data Source
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AI summary
The present invention relates to a method of lowering an output voltage of each submodule, which has not broken down, of converter arms, in a MMC for HVDC where redundancy modules for enhancing a rate of operation are applied, when a breakdown of a submodule of the MMC occurs in a case where there is no more redundancy module to be applied, whereby a system may continuously operate. According to the present invention, there is provided a redundancy control method of an MMC for HVDC, wherein the MMC includes multiple converter arms each has multiple submodules in operation and redundancy modules for spares, the method including: checking whether a breakdown of a submodule in operation of a first converter arm among the multiple converter arms occurs in a case where the all redundancy modules of the first converter arm are applied in operation; and lowering an output voltage of each submodule of other converter arms in such a manner that a DC link voltage of each of the other converter arms is controlled to be equal to a DC link voltage of the first converter arm when the breakdown of the submodule of the first converter arm occurs.