MMC Module Bypass Assembly for Fast Fault Current Diversion

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Solution Overview

Problem

In modular multilevel power converters, mechanical bridging switches take time to activate, leading to unwanted charging of energy storage devices during faults, which can cause damage and explosive heat release when discharged, due to their mechanical inertia and sudden current reversal.

Innovation Solution

Incorporating an electronic switching unit in parallel with the mechanical bridging switch, which can quickly assume a conductive state to divert current before the mechanical switch activates, reducing overcharging and minimizing module damage by using IGBTs or similar power semiconductor components with a gentle switch-on characteristic.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a mechanical bypass switch is used to bridge the module in the event of a fault, then the module can be bypassed and the converter can continue operating, but the mechanical inertia causes delayed activation and further charging of the energy storage device

Engineering Contradiction:

Improvemodule bypassing capabilityVSAvoidswitching activation time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the purely mechanical bypass switch with a hybrid system that uses an electronic switching unit (semiconductor-based) to perform the bypass function. This substitution eliminates mechanical inertia delays while maintaining the bypass capability, allowing the module to be bridged almost instantly upon fault detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The electronic switching unit acts as an intermediary between the fault condition and the mechanical bypass switch. It activates first to provide immediate protection against further energy storage charging, then transfers control to the mechanical switch which provides a stable, low-loss bypass path.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the mechanical bypass switch is used, then the module can be bypassed, but the sudden current reversal and explosive heat release can cause damage

Engineering Contradiction:

Improvemodule bypassing capabilityVSAvoidheat release and current reversal damage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The electronic switching unit performs preliminary action by activating before the mechanical switch to prevent further charging of the energy storage device. This preliminary protection measures reduces the stored energy to a safe level before the mechanical switch closes, preventing explosive heat release and current reversal damage.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The electronic switching unit provides beforehand cushioning by gradually managing the energy storage device charging process before the mechanical switch operates. This cushioning effect prevents sudden energy release and protects the module from harmful thermal and electrical stress.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Loss of time

If the electronic switching unit continuously carries the current, then the module can be bypassed quickly, but the losses in the electronic switching unit would be high

Engineering Contradiction:

Improvebypass activation speedVSAvoidswitching unit power losses

Core Design Contradiction:

Loss of timeVSLoss of energy

Solution Approach 1:

The system uses periodic action by having the electronic switching unit activate temporarily only during the fault condition and energy transfer phase, then transfer control to the mechanical bypass switch for continuous operation. This periodic engagement minimizes energy losses while maintaining fast response capability.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system dynamically transitions between two bypass modes: electronic switching for immediate fault response and mechanical switching for stable continuous operation. This dynamic allocation optimizes both speed and efficiency by using each component in its most suitable operating regime.

Inventive Principle:

Principle #15Dynamics

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 solution allows for early and gentle diversion of current, reducing the risk of overcharging and module damage, while ensuring reliable bypassing with lower losses and improved reliability of the mechanical bridging switch, allowing the power converter to continue operating safely.

Implementation Method 1

using IGBTs or similar power semiconductor components with a gentle switch-on characteristic

Methodology Applied

Scientific EffectSemiconductor switching:

Data Source

PatentEP3818549B1Assembly comprising a module of a multi-level converter

Publication Date: 2024.11.13 SIEMENS ENERGY GLOBAL GMBH & CO KG

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AI summary

The invention relates to an assembly comprising a module (200) of a modular multi-level converter (1), which has a first module connection (212), a second module connection 9(215), a first electronic switch element (202), a second electronic switch element (206) and an electrical energy store (210). The assembly also comprises a mechanical bypass switch (220) arranged between the first module connection (212) and the second module connection (215) and electrically bypassing the module in the its switched-on state, and an electronic switch unit (410) arranged between the first module connection (212) and the second module connection (215) and electrically bypassing the module in theits switched-on state.