MMC Converter Cell Layout for Overvoltage and Fault Current Control
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Solution Overview
Problem
Existing modular multilevel converters (MMCs) face challenges in maintaining capacitor voltage stability to prevent overvoltage and suppressing short-circuit currents, which can lead to operational failures and component degradation, while existing solutions are space and cost-inefficient.
Innovation Solution
A power conversion device with a hybrid configuration of full-bridge and half-bridge converter cells, incorporating a resistor element in series with semiconductor switching elements in specific arms, to manage overvoltage and short-circuit currents efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC chopper with a series circuit including a semiconductor switch and a resistor is connected in parallel with a power storage element of each converter cell to prevent overvoltage, then overvoltage protection is improved, but device complexity and space occupation increase
Solution Approach 1:
The patent integrates the overvoltage protection function into the existing full-bridge converter cell structure by utilizing the fourth arm (which would otherwise be unused in half-bridge cells) to connect the resistor element. This allows the same circuit structure to serve both as a power conversion component and an overvoltage protection mechanism, eliminating the need for separate DC chopper circuits and reducing overall device complexity
Solution Approach 2:
The patent combines the overvoltage protection function with the power conversion function by integrating the resistor element into the full-bridge converter cell configuration. The fourth arm of the full-bridge cell, which provides an otherwise unused pathway, is merged with the protection circuit requirements, allowing simultaneous achievement of power conversion and overvoltage protection without additional space-consuming separate circuits
2Reliability
If a DC chopper with a series circuit including a semiconductor switch and a resistor is connected in parallel with a power storage element of each converter cell to prevent overvoltage, then overvoltage protection is improved, but cost increases
Solution Approach 1:
The patent makes the full-bridge converter cell structure serve multiple purposes: power conversion during normal operation and overvoltage protection during abnormal conditions. By utilizing the fourth arm for protection functions, the same hardware components perform dual roles, eliminating the need for additional expensive separate protection circuits and reducing overall manufacturing cost
Solution Approach 2:
The patent merges the protection circuit requirements with the power conversion circuit structure. The resistor element and switching mechanism are integrated into the existing full-bridge cell architecture, allowing shared use of components for both power conversion and protection functions, thereby reducing material costs and manufacturing complexity
3Reliability
If half of converter cells have a full-bridge configuration and the other half have a half-bridge configuration to suppress short-circuit current, then short-circuit current suppression is improved, but device complexity increases
Solution Approach 1:
The patent applies full-bridge configuration selectively only to converter cells that require overvoltage protection capability, rather than uniformly across all cells. This localized application of the more complex full-bridge structure minimizes the number of cells needing this configuration, thereby reducing overall device complexity while maintaining adequate short-circuit current suppression where needed
Solution Approach 2:
The patent changes the configuration parameter (bridge type) of converter cells based on their functional requirements. Converter cells needing overvoltage protection use full-bridge configuration with four switching elements, while other cells use the simpler half-bridge configuration with two switching elements. This parameter variation optimizes the balance between protection capability and device complexity
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
The hybrid configuration effectively prevents overvoltage and suppresses short-circuit currents in a space-efficient manner, ensuring stable operation and reducing the risk of component failure.
Implementation Method 1
the second arm or the third arm includes a resistor element connected in series with the semiconductor switching element
Data Source
AI summary
A power conversion device includes a power converter including an arm circuit having a plurality of converter cells connected in cascade. Each of the converter cells includes a bridge circuit including a plurality of semiconductor switching elements, and a power storage element connected to a first input/output terminal on a high potential side and a second input/output terminal on a low potential side through the bridge circuit. One or more of the converter cells are full-bridge converter cells. Among four arms that constitute the bridge circuit of the full-bridge converter cell, an arm between a high potential-side node of the power storage element and the second input/output terminal, or an arm between a low potential-side node of the power storage element and the first input/output terminal includes a resistor element connected in series with the semiconductor switching element.