Transformerless Converter DC Fault Isolation for Earth Fault Protection
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Solution Overview
Problem
Transformerless converters are vulnerable to ground faults, which can cause significant damage due to uncontrollable ground fault currents, leading to potential safety hazards and system downtime, as conventional protection methods like DC fuses and overcurrent protection are inadequate.
Innovation Solution
Incorporating an additional unidirectional semiconductor switch with a unidirectional switching element in the DC lines of the converter, which is quickly activated to interrupt ground fault circuits, preventing the flow of ground fault currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If transformerless converter design is used to eliminate transformer, then cost and space are reduced and efficiency is improved, but vulnerability to ground faults increases causing serious damage and safety hazards
Solution Approach 1:
The patent applies preliminary action by pre-configuring the unidirectional switching element and unidirectionally conducting semiconductor switch in the converter circuit before a ground fault occurs. These components are designed to automatically activate when a ground fault is detected, interrupting the ground fault current path before it can cause serious damage. This preventive measure allows the converter to maintain transformerless design (saving cost and space) while gaining ground fault protection capability.
2Reliability
If DC fuses or pyrotechnic isolating elements are used for ground fault protection, then ground fault currents are interrupted, but service intervention is required causing system downtime and additional complexity
Solution Approach 1:
The patent implements self-service by designing a protection system that automatically detects ground faults and interrupts the fault current without requiring external service intervention. The unidirectional switching element combined with the unidirectionally conducting semiconductor switch creates a self-acting protection mechanism that responds autonomously to ground fault conditions, eliminating the need for manual fuse replacement or service calls, and avoiding system downtime.
3Reliability
If overcurrent protection is implemented to monitor maximum AC current, then internal inverter fault currents are prevented, but ground fault currents can still persist causing damage
Solution Approach 1:
The patent applies segmentation by dividing the protection function into two independent parts: (1) overcurrent protection for monitoring maximum AC current and preventing internal inverter fault currents, and (2) ground fault protection using the unidirectional switching element and unidirectionally conducting semiconductor switch to specifically target and interrupt ground fault currents. This segmented approach allows each protection mechanism to specialize in its specific threat without interfering with the other, ensuring comprehensive protection against both internal faults and ground faults.
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
Effectively protects the converter from ground faults by rapidly interrupting ground fault currents, preventing damage to the converter and associated components, and ensuring safety by blocking hazardous contact voltages.
Implementation Method 1
a unidirectional switching element DT1, DT2, in particular a diode, is connected in parallel to the at least one further unidirectionally conductive semiconductor switch T1, T2
Data Source
Figure 1
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AI summary
In order to be able to effectively protect a transformerless converter (1) against the effects of an earth fault (10), it is provided that in a connecting line (V+, V-) of the converter (1), which connects an intermediate circuit connection pole (ZK+, ZK-) of the DC voltage intermediate circuit (6) to a DC connection pole (DC+, DC-) of the DC connection (3), a further unidirectionally conductive semiconductor switch (T1, T2) is provided, which interrupts the connecting line (V+, V-) when the further unidirectionally conductive semiconductor switch (T1, T2) is open and, when the further unidirectionally conductive semiconductor switch (T1, T2) is closed, switches the connecting line (V+, V-) conductive in a first current flow direction from the AC connection (2) to the DC connection (3) and blocks it against the first current flow direction, wherein a unidirectional switching element (DT1, DT2) is connected in parallel to the further semiconductor switch (T1, T2), which in the first current flow direction blocks and conducts opposite to the first current flow direction.