Overvoltage Protection for Current Fed Converters via di/dt Sensing
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Solution Overview
Problem
Current fed converters face significant challenges with overvoltage protection due to current interruptions, which can lead to converter breakdowns, and existing protection circuits are bulky, inefficient, and often fail to detect faults in time, leading to increased losses and damage.
Innovation Solution
A method involving the measurement of current derivative signals to detect potential overvoltage conditions, using low-voltage analog and logic circuits to trigger a protection mechanism that ensures a freewheeling path for the DC link current, thereby preventing voltage rises and reducing the need for bulky power devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If usual protection circuits with multiple power devices (diode, TVS, thyristor, MOV) are used to clamp overvoltage, then the converter is protected against voltage breakdown, but the circuit becomes bulky and increases switching losses due to parasitic elements
Solution Approach 1:
The patent extracts the essential protection function from complex multi-device circuits and implements it using a single power device (IGBT or MOSFET) controlled by a microcontroller. The microcontroller monitors voltage and current, detects fault conditions, and activates the power device to create a freewheeling path, eliminating the need for bulky passive protection components while maintaining reliability
Solution Approach 2:
The microcontroller serves multiple functions: it monitors voltage and current, detects overvoltage conditions, controls the power device switching, and manages the freewheeling path. This multi-functional approach replaces multiple dedicated protection components with a single intelligent control unit, reducing circuit complexity
2Productivity
If fast IGBT devices are used to improve switching speed and reduce losses, then converter efficiency improves, but the response time for protection features must be reduced even further to prevent destruction during current interruption
Solution Approach 1:
The microcontroller continuously monitors voltage and current before fault conditions occur, maintaining readiness to detect anomalies. When a current interruption is detected, the system has already prepared the protection mechanism, enabling immediate activation of the freewheeling path without delay, thus matching the fast response capability of modern IGBT devices
3Reliability
If protection circuits conduct part of the power current, then overvoltage is clamped, but additional losses are introduced in Current Source Inverters
Solution Approach 1:
The protection device operates in periodic switching mode rather than continuous conduction. The microcontroller activates the power device only during brief intervals when overvoltage conditions occur, allowing the device to switch on and off rapidly. This periodic action provides necessary overvoltage protection while minimizing the time the protection circuit conducts current, thereby reducing energy losses
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 enables fast and effective overvoltage protection in current fed converters by identifying the root cause of current interruptions, reducing the risk of converter damage and minimizing losses by using fewer and more efficient power devices.
Implementation Method 1
measuring current derivative signals di/dt in respective upper switching devices or lower switching devices
Data Source
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Figure 3A~3B
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AI summary
The disclosure concerns a method for protecting against overvoltage a current fed converter, comprising a switching cell having two or more legs, each leg being provided with at least one switching device (31, 32, 41, 42), in an open circuit failure condition of a switching device in a leg of said switching cell, comprising - measuring (110) current derivative signals dlo/dt in respective upper switching devices (41, 42) or lower switching devices (31, 32) of at least two of said legs where a switching transition (ST1, ST2) occurs, said switching transition comprising a change of current conducting switching device (Q1, Q3) within said upper switching devices (41, 42) or lower switching devices (31, 32) and - triggering a protection, based on said current derivative signals, when either: o the absolute value of one of said current derivative signal being lower than a first predefined value k1 or null, or o a sum of the absolute values of said current derivative signals being lower than a second predefined value k2, during said switching transition. The disclosure also concerns an electronic circuit configured for implementing the method.