MMC Module Thyristor Bypass for Diode Fault Current Relief
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Solution Overview
Problem
In modular multilevel converters, short-circuit currents can overload diodes during faults, necessitating a solution to relieve diode load while maintaining converter operation.
Innovation Solution
A module design incorporating a thyristor element with an antiparallel circuit of thyristors, which acts as both a bypass switch and a load relief mechanism for diodes, allowing the module to be structured compactly and efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bypass switch and additional component are added to relieve diode load during faults, then diode reliability is improved, but device complexity increases
Solution Approach 1:
The patent combines the bypass switch function and diode protection function into a single thyristor element. The thyristor is connected in antiparallel with the diode, allowing it to serve dual purposes: bypassing faults and limiting reverse voltage/current to protect the diode during short-circuit conditions, thereby reducing overall device complexity while maintaining reliability
Solution Approach 2:
The thyristor element is designed to perform multiple functions simultaneously: it acts as a bypass switch for fault current, a voltage limiter for diode protection, and a controlled switching element. This multi-functionality eliminates the need for separate dedicated protection components, resolving the contradiction between reliability improvement and complexity reduction
2Volume of moving object
If thyristors are arranged in antiparallel circuit between conductors, then space utilization is improved, but manufacturing complexity increases
Solution Approach 1:
The thyristors are arranged in a nested configuration within the existing module structure, utilizing the space between the first and second electrical conductors. The antiparallel-connected thyristors are integrated into the compact layout, maximizing space utilization while maintaining manufacturability through standardized mounting patterns
Solution Approach 2:
The thyristors are positioned in specific locations where they can effectively perform their functions: between the conductors where magnetic fields are strongest for optimal triggering, and in antiparallel configuration for balanced current sharing. This localized optimization achieves compact design without compromising manufacturing ease
3Reliability
If thyristors are positioned in strong magnetic field regions, then triggering reliability is improved, but susceptibility to magnetic interference increases
Solution Approach 1:
The patent utilizes the strong magnetic fields generated by the electrical conductors during operation to trigger the thyristors. The magnetic fields that could be considered harmful interference are instead harnessed as the triggering mechanism for the thyristors, converting a potential problem into a beneficial automatic switching function during fault conditions
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 solution effectively reduces diode loading during faults by redirecting fault currents through the thyristor element, enabling continuous converter operation without the faulty module and improving energy efficiency.
Implementation Method 1
a current that switches on the first thyristor is induced in the semiconductor material due to a magnetic field that changes over time, said magnetic field arising due to a discharge current of the energy storage unit that flows through the first electrical conductor and/or the second electrical conductor and permeating the semiconductor material of the first thyristor
Data Source
AI summary
A module of a modular multi-level converter includes a first module terminal, a second module terminal, a first electrical conductor, a second electrical conductor, a third electrical conductor, a power semiconductor circuit and an electrical energy storage unit. The power semiconductor circuit has a first electronic switching element and a second electronic switching element. A first diode is connected in anti-parallel with the first electronic switch element and a second diode is connected in anti-parallel with the second electronic switching element. The power semiconductor circuit is connected to the energy storage unit by the first electrical conductor and the second electrical conductor. The first module terminal is connected to the third electrical conductor. A first thyristor and a second thyristor are connected between the third electrical conductor and the second electrical conductor, The first thyristor and the second thyristor forming an anti-parallel circuit.