DC Link Capacitor Rogowski Sensing for Fast Over-Current Shutdown
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Solution Overview
Problem
Existing electrical power converters rely on desaturation detection, which has insufficient response time for fast-switching technologies like Silicon Carbide switches and is prone to false triggering due to temperature variations and noise, making them unreliable for over-current protection.
Innovation Solution
Implementing an inductive current sensor, such as a Rogowski coil, to detect primary current from a DC link capacitor, providing fast and accurate over-current detection by sensing magnetic flux, independent of switch on-resistance and temperature, and using a detection circuit to switch off semiconductor switches when an over-current condition is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If desaturation detection is used to monitor switch on-state voltage, then over-current protection is provided, but the response time is too slow (3 μs or more) for fast-switching technologies like Silicon Carbide switches
Solution Approach 1:
The patent replaces voltage-based desaturation detection with current-based Rogowski coil detection. The Rogowski coil uses electromagnetic induction to sense current directly, eliminating the need to monitor voltage changes across the switch's on-resistance. This substitution of detection methodology achieves response times under 350 ns, making it suitable for fast-switching Silicon Carbide devices.
Solution Approach 2:
The Rogowski coil acts as an intermediary sensing element that magnetically couples to the current-carrying conductor without electrical contact. This intermediary approach allows non-intrusive current measurement with extremely fast response, as the coil感应s the magnetic field changes produced by the switch current without being affected by voltage spikes or parasitic elements in the switch circuit.
2Reliability
If desaturation detection relies on voltage detection, then over-current can be detected, but false triggering occurs due to noise induced voltage spikes from parasitic elements and temperature variations
Solution Approach 1:
The patent substitutes voltage-based detection with magnetic field-based detection using the Rogowski coil. Since the coil senses current through electromagnetic induction rather than voltage measurement, it is immune to voltage spikes caused by parasitic inductance and resistance in the circuit layout. The magnetic coupling provides inherent noise rejection and eliminates false triggering from switching transients.
Solution Approach 2:
The Rogowski coil creates an electrically inert sensing environment by magnetically coupling to the current conductor without electrical connection. This isolation from the high-voltage, high-noise switch node protects the detection circuit from electromagnetic interference and voltage transients, providing stable and reliable current measurement regardless of switching conditions or temperature variations.
3Measurement precision
If desaturation detection uses switch on-resistance to detect excessive voltage, then current detection is achieved, but performance is inconsistent across the working temperature range due to varying on-resistance
Solution Approach 1:
The patent replaces detection methods that depend on switch parameters (on-resistance) with a method that directly senses current through magnetic coupling. The Rogowski coil's output is proportional to the rate of change of current (di/dt) and is independent of the switch's temperature-dependent on-resistance. This provides consistent current measurement accuracy across the full operating temperature range.
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 achieves rapid over-current protection, reducing false triggering and ensuring consistent performance across temperature ranges, particularly beneficial for Silicon Carbide switches, with response times under 350 ns, and integrates seamlessly with existing systems.
Implementation Method 1
an inductive current sensor, such as a Rogowski coil, to detect primary current from a DC link capacitor, providing fast and accurate over-current detection by sensing magnetic flux
Data Source
AI summary
An electrical power converter (1, 1′, 1″) includes a DC link capacitor (3, 3′, 3″) configured for connection to a DC power source to provide an input load, at least one pair of semiconductor switches (2a, 2b, 2c, 2a′, 2b′, 2a″, 2b″) connected in parallel with the DC link capacitor (3, 3′, 3″) and positioned on either side of an output load terminal (10a, 10b, 10c, 10a′, 10b′, 10a″, 10b″). The electrical power converter (1, 1′, 1″) further includes an inductive current sensor (12, 12′, 12″), arranged to sense a primary current from a terminal of the DC link capacitor (3, 3′, 3″), and a detection circuit (14), connected to the inductive current sensor (12, 12′, 12″) and arranged to monitor for an over-current condition, and to produce an output which causes at least one of the pair of semiconductor switches (2a, 2b, 2c, 2a′, 2b′, 2a″, 2b″) to be switched to a non-conducting state when an over-current condition is detected.