Auxiliary Gate Drive Circuit for Early MOSFET Desaturation Detection
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Solution Overview
Problem
Existing control devices for gate transistors in inverters used in electric propulsion systems of aircraft suffer from delays in detecting short circuits, which can lead to damage of SiC MOSFET transistors due to insufficient reactivity and increased switching losses, and require costly modifications to improve responsiveness.
Innovation Solution
An auxiliary circuit is integrated with the control device, featuring an auxiliary comparator circuit for early detection of desaturation and a two-stage switching mechanism to rapidly open the gate transistor, allowing for reactive protection of SiC MOSFETs while maintaining compatibility with IGBT transistors, using discrete components to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional control device with integrated circuit is used, then the device complexity is reduced and manufacturing cost is lowered, but the detection speed of short circuit is too slow causing SiC MOSFET damage
Solution Approach 1:
The control device is segmented into two independent parts: a simple main circuit (integrated circuit) and a separate auxiliary circuit (discrete electronic components). The auxiliary circuit handles fast desaturation detection and generates early warning signals, while the main circuit continues normal gate control. This segmentation allows the system to achieve fast detection speed through the auxiliary circuit without increasing the complexity of the main control device.
Solution Approach 2:
The auxiliary circuit acts as an intermediary between the main circuit and the gate transistor. It monitors the drain voltage and detects desaturation conditions before they cause damage, then sends early warning signals to the main circuit. This intermediary function enables fast detection and protective action without requiring the main integrated circuit to be redesigned for high-speed detection.
2Speed
If the gate transistor opens too quickly to prevent short circuit damage, then the protection speed is improved, but overvoltage is generated exceeding avalanche voltage causing transistor destruction
Solution Approach 1:
The auxiliary circuit performs preliminary detection of desaturation conditions by monitoring drain voltage before the short circuit causes damage. By detecting desaturation early (within 0.6 μs for SiC MOSFETs), the system can initiate controlled opening sequences before excessive current or voltage damage occurs, preventing both slow opening damage and overvoltage destruction.
Solution Approach 2:
The auxiliary circuit continuously monitors the drain voltage and provides real-time feedback about saturation status. When desaturation is detected, this feedback triggers the main circuit to modify its gate control signal, creating a feedback loop that enables controlled opening at optimal speeds to prevent both short circuit damage and overvoltage conditions.
3Use of energy by moving object
If SiC MOSFET transistors are used to improve inverter performance, then the power efficiency is improved, but the cost increases and they require faster protection response
Solution Approach 1:
The control system dynamically adapts its response based on the transistor type and operating conditions. The auxiliary circuit provides dynamic monitoring and the main circuit modifies gate control signals in real-time based on feedback. This dynamic control enables the system to provide the ultra-fast protection response (less than 0.6 μs) that SiC MOSFETs require, ensuring their reliability while maintaining their high power efficiency benefits.
Data Source
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AI summary
An auxiliary circuit (200b) for a control device of a power transistor (T2), the auxiliary circuit (200b) being configured to connect to the gate and drain of the gate transistor (T2), the auxiliary circuit (200b) being configured to receive from a main circuit (200a) at least one switching command (OUT_H, OUT_B) and output a gate command (GRDV), the auxiliary circuit (200b) being configured to output a nominal desaturation voltage (DESAT), the auxiliary circuit (200b) comprising at least one auxiliary comparator circuit (224) configured to compare a voltage representative of a drain voltage (VDS), to an advanced desaturation threshold (Vth) so as to achieve early detection of desaturation, the auxiliary circuit (200b) being configured to modify the gate command (GDRV) in case of early detection.