IGBT Gate Driver Turn-Off Control for Surge Voltage and Losses
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Solution Overview
Problem
Existing drivers for voltage-driven switching elements, such as IGBTs, face issues with excessive surge voltage during turn-off, leading to heat damage and unnecessary switching losses due to a fixed, constant change rate of collector voltage, which does not adapt to varying power voltages.
Innovation Solution
A driver circuit with a discharge circuit and a delay circuit that controls the discharge rate of the gate charge, allowing a higher initial change rate during turn-off followed by a lower rate after a prescribed delay, ensuring the collector voltage does not exceed the rating while minimizing switching losses by adapting to the power voltage level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the discharge rate of gate charge is controlled to limit the change rate of collector voltage to a constant value, then excessive surge voltage is prevented, but switching losses increase due to unnecessarily low switching rate
Solution Approach 1:
The patent applies dynamics by making the discharge rate adaptive rather than fixed. The discharge rate controller dynamically adjusts the gate charge discharge rate based on real-time collector voltage feedback. When collector voltage is low, a higher discharge rate is permitted; when collector voltage approaches the power source voltage, the discharge rate is reduced. This dynamic adjustment optimizes switching performance while preventing surge voltage, resolving the contradiction between fixed-rate protection and variable-rate efficiency.
Solution Approach 2:
The patent changes the parameter of discharge rate from a constant value to a variable value that depends on collector voltage level. The discharge rate controller modifies the discharge rate parameter in response to collector voltage conditions, allowing the system to transition from a static control mode (which causes excessive switching losses) to a dynamic control mode that adapts to instantaneous operating conditions, thereby reducing energy loss while maintaining surge protection.
2Reliability
If a fixed change rate of collector voltage is maintained, then voltage rating is not exceeded, but switching speed is reduced leading to higher switching losses
Solution Approach 1:
The patent changes the control parameter from a fixed change rate to a variable change rate that adapts to collector voltage conditions. The discharge rate controller continuously adjusts the gate charge discharge rate based on collector voltage feedback, allowing faster switching when voltage headroom is available and slower switching when approaching the voltage rating. This parameter adaptation maintains reliability while maximizing switching speed.
Solution Approach 2:
The system transitions from static voltage rate control to dynamic voltage rate control. The discharge rate controller dynamically responds to collector voltage changes, enabling the switching element to operate at maximum safe speed at all times rather than being constrained by a predetermined conservative rate. This dynamic approach simultaneously improves switching speed and maintains voltage rating compliance.
3Object-affected harmful factors
If the discharge rate is reduced to prevent surge voltage, then voltage rating is protected, but turn-off time increases causing higher switching losses
Solution Approach 1:
The patent changes the discharge rate from a uniformly low value to a variable value that is high when collector voltage is low and reduces only when necessary. The discharge rate controller adjusts the discharge rate parameter in real-time, allowing rapid turn-off during the initial phase when surge voltage risk is minimal, and applying rate limitation only during the critical phase when collector voltage approaches the power source voltage. This selective parameter adjustment minimizes turn-off time while preventing voltage rating exceedance.
Solution Approach 2:
The turn-off process is segmented into different phases with different discharge rate requirements. The discharge rate controller divides the turn-off operation into an initial phase (where high discharge rate is safe and beneficial) and a critical phase (where rate limitation is necessary). This segmentation allows the system to optimize each phase independently, reducing overall turn-off time while maintaining protection against voltage rating exceedance.
Data Source
AI summary
A driver apparatus and method for driving a voltage driven type switching element that discharge an electrical charge stored at the gate terminal of the voltage driven type switching element at a discharge rate. The discharge rate is controlled so that the change rate over time of the voltage between the collector and emitter terminals of the voltage driven type switching element is limited to a second change rate during the turn-off operation. The starting time of the control of the change rate over time to attain the second change rate is delayed for a predetermined delay time after start of the turn-off operation and before a time when the voltage between the collector and emitter terminals first reaches the power source voltage level. During the delay time, the discharge rate is initially at a first change rate higher than the second change rate.