MMC Submodule State Diagnosis During Initial Charging
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Solution Overview
Problem
Existing methods for diagnosing submodule states in modular multilevel converters (MMC) during initial charging are inadequate, particularly in preventing explosions due to faulty submodules and require additional devices, which complicates the process.
Innovation Solution
A method involving an upper level controller that supplies AC voltage to submodules, determines initial charging voltages, and diagnoses submodule states by identifying fault signals and voltage differences, allowing for the identification of faulty submodules before operation without additional devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional devices are added to diagnose submodule states during initial charging, then diagnostic capability is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by utilizing the existing voltage detection units and control circuits within the MMC converter system to perform initial charging voltage detection. The submodule controllers use built-in resources to detect voltages during initial charging without requiring external diagnostic equipment, thereby improving reliability while avoiding increased device complexity
Solution Approach 2:
The voltage detection units and control circuits are designed to serve multiple functions: they detect voltages during normal operation and also detect initial charging voltages during startup. This multi-functionality allows the system to perform diagnostic capabilities using existing components rather than adding dedicated diagnostic devices
2Object-affected harmful factors
If submodule state diagnosis is performed during initial charging, then safety is improved by preventing explosions, but measurement precision requirements increase
Solution Approach 1:
The patent applies preliminary action by detecting the initial charging voltage of each submodule during the startup phase before the converter begins normal operation. By performing voltage detection at this early stage, the system identifies faulty submodules that may have charging issues, capacitor defects, or connection problems before they can cause harmful effects during operation
Solution Approach 2:
The system implements feedback by comparing the detected initial charging voltage with expected voltage values and using this information to determine submodule health status. The control circuit receives voltage information from detection units and uses this feedback to identify faulty submodules, enabling safety measures to be taken before harmful effects occur
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the determination of submodule states during initial charging, preventing explosions and ensuring stable operation by identifying and addressing faulty submodules before normal operation, thereby enhancing safety and efficiency.
Implementation Method 1
charging a capacitor in the submodule with the supplied AC voltage to store an initial charging voltage in the capacitor
Data Source
AI summary
A method for diagnosing a state of a submodule in initial charging of an MMC converter includes identifying, by an upper level controller, a stopped state of the MMC converter; supplying, by the upper level controller, an alternating current (AC) voltage from an AC side to N submodules in the MMC converter when the MMC converter is in the stopped state; charging a capacitor in the submodule with the supplied AC voltage to store an initial charging voltage in the capacitor; determining, by a submodule controller, whether the submodule is in a fault state and when the submodule is in a fault state, transmitting a fault signal to the upper level controller; and detecting, by a voltage detection unit of the submodule the initial charging voltage stored in the capacitor and transmitting the initial charging voltage to the submodule controller.