IGBT Gate Turn-Off Control Using a Desaturation Voltage Step
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Solution Overview
Problem
Conventional methods for turning off bipolar switchable power semiconductor components, such as IGBTs, result in high turn-off losses due to direct reduction of gate voltage from a high to a low value, limiting switching speed and increasing electrical field strengths.
Innovation Solution
A control device that reduces the gate voltage from a first value to a desaturation value greater than the pinch-off voltage before lowering it to the second value, using a pulse-width modulation approach to efficiently discharge charge carriers and minimize turn-off losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the gate voltage is directly reduced from the first voltage value to the second voltage value, then the turn-off process is completed quickly, but high turn-off losses occur due to high charge carrier concentration
Solution Approach 1:
The gate voltage reduction process is segmented into two distinct phases: first reducing from the first voltage value to a desaturation value (greater than pinch-off voltage), then reducing from the desaturation value to the second voltage value. This segmentation allows charge carriers to be dispelled in a controlled manner, reducing turn-off losses while maintaining manageable device complexity through structured control sequences.
Solution Approach 2:
The first voltage reduction phase acts as a preliminary action that prepares the power semiconductor component for the second phase. By initially reducing the gate voltage to the desaturation value, charge carriers are partially dispelled and the component is prepared for the final turn-off, thereby reducing the energy losses in the subsequent phase.
2Productivity
If the switching speed is increased to minimize turn-off losses, then the efficiency is improved, but high electrical field strengths are generated that limit the switching speed
Solution Approach 1:
The first voltage reduction phase serves as a preliminary action that reduces charge carrier concentration before the final turn-off. This preliminary reduction of charge carriers enables faster switching in the second phase without generating excessive electrical field strengths, as there are fewer charge carriers to create high fields during the rapid voltage transition.
Solution Approach 2:
The control device dynamically adjusts the gate voltage in two phases, adapting the switching process to the changing charge carrier concentration. This dynamic control allows the system to achieve high switching speeds while maintaining electrical field strengths within safe operating limits by coordinating voltage reduction with charge carrier dispelling.
3Ease of operation
If the gate voltage is reduced to the second voltage value directly, then the control process is simple, but high turn-off losses occur due to the transition from high charge carrier concentration to de-energized state
Solution Approach 1:
The control process is segmented into two voltage reduction phases, which adds some complexity to the control sequence but significantly reduces turn-off losses. The segmentation allows for optimized control of charge carrier dispelling, making the additional control steps worthwhile for achieving lower energy losses.
Solution Approach 2:
The gate voltage parameter is changed in two distinct steps rather than directly, with the first step reducing to a desaturation value and the second step completing the turn-off. This parameter change strategy optimizes the balance between control complexity and energy loss reduction by using intermediate voltage levels to manage charge carrier concentration effectively.
Data Source
AI summary
A control device for driving a bipolar switchable power semiconductor component is designed to apply an electrical voltage to a gate terminal of the power semiconductor component and to reduce the electrical voltage for turning off the power semiconductor component from a first voltage value to a second voltage value. The control device is designed, for turning off the power semiconductor component, firstly to reduce the electrical voltage from the first voltage value to a desaturation value and then to reduce the electrical voltage from the desaturation value to the second voltage value. The desaturation value is greater than a pinch-off voltage of the power semiconductor component.