Modular Multilevel Converter Startup with Half-Bridge Cell Charging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modular multilevel converters often fail to start operation due to insufficient initial cell voltage, which can vary across different converter configurations, leading to challenges in designing a power supply that ensures proper energization of cell capacitors.
Innovation Solution
A method for energizing modular multilevel converters involves providing power from an external supply, charging cells, generating a sub-ready signal when cell voltage exceeds a first threshold, and running a deblocking sequence to configure cells as half-bridge cells until reaching an operable voltage, reducing dependency on converter configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed power supply design is used for cell charging, then the design is simple and cost-effective, but it cannot ensure sufficient charging for all converter configurations
Solution Approach 1:
The patent implements a dynamic charging methodology that adapts the charging process based on real-time cell voltage measurements. The system transitions from a static blocking mode to an active deblocking sequence with controlled switch operations, enabling the power supply to dynamically adjust its behavior to achieve sufficient cell voltage across different converter configurations
Solution Approach 2:
The patent changes the operating parameters of the converter cells during the charging process. By transitioning cells from blocking mode to half-bridge mode through controlled switch operations, the system modifies the electrical parameters (impedance, voltage distribution) to enable effective charging regardless of the initial converter configuration
2Device complexity
If all switches remain open during charging (blocking mode), then the charging process is simple, but the cell voltage cannot reach the required level for proper operation
Solution Approach 1:
The patent implements a preliminary deblocking sequence that prepares the converter cells for proper operation before full startup. By pre-charging cells using controlled switch operations and transitioning through half-bridge mode, the system ensures that all necessary voltage levels are achieved before normal operation begins
Solution Approach 2:
The patent segments the charging process into distinct phases: initial blocking mode charging, deblocking sequence with controlled switch operations, half-bridge mode charging, and final ready-for-operation state. This segmentation allows each phase to be optimized independently, ensuring reliable voltage buildup
3Productivity
If the MMC is deblocked early, then the startup process is faster, but the control boards and gate drive units may not have sufficient power
Solution Approach 1:
The patent implements feedback mechanisms where control boards continuously monitor cell voltage levels and provide status signals (sub-ready, ready-for-operation) to the control system. This feedback ensures that deblocking and startup operations only proceed when sufficient voltage is confirmed, guaranteeing reliable control function operation
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
This approach ensures consistent and reliable startup of modular multilevel converters across various configurations by ensuring cell capacitors reach a sufficient voltage for proper operation, independent of initial cell voltage levels.
Implementation Method 1
powering the cells, thereby charging the chargeable elements of the cells
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The present disclosure relates to a method for energizing a modular multilevel converter (100) comprising converter valves (101), each converter valve having a plurality of interconnected cells (102), wherein each cell comprises a plurality of power electronic switches (105, 106, 107, 108) in a full-bridge arrangement, a chargeable element (109), and a plurality of gate drive units (118), one gate drive unit for each power electronic switch. The method includes: providing power to the modular multilevel converter from an external power supply (S201); powering the cells, thereby charging the chargeable elements of the cells (S202); generating, when a cell voltage caused by said charging exceeds a first threshold voltage level, a cell sub-ready signal for that cell (S203); generating, when at least a predetermined minimum number of cells have generated the sub-ready signal, a sub-ready_for_operation signal (S204); and running a deblocking sequence comprising closing a first power electronic switch (105) in all cells to electrically configure the cells to be continuously charged as a half-bridge cells, and keep the first power electronic switch closed until the cell voltage has reached a converter operable voltage, which is higher than a second threshold voltage (S205).