IGBT Gate Charge Control to Prevent Dynamic Avalanche
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Solution Overview
Problem
High electric field strengths during the switching off of IGBTs can lead to dynamic avalanche, causing spontaneous failure or long-term degeneration, especially at high reverse voltages, and existing solutions that reduce switching speed increase turn-off losses.
Innovation Solution
A method and gate driver that control the charge removal from the IGBT gate by determining a specific charge range between minimum and maximum extraction charges, applying a turn-off voltage, and measuring the gate current to limit the charge removal to prevent dynamic avalanche without reducing switching speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching speed of the IGBT is reduced, then the electric field strength load on the IGBT is reduced and dynamic avalanche is prevented, but the turn-off losses increase
Solution Approach 1:
The patent applies preliminary action by determining and specifying the minimum and maximum extraction charges before the switching operation. The gate charge is controlled to remain within this predetermined range, ensuring that the electric field strength stays below the dynamic avalanche threshold while maintaining sufficient switching performance. This pre-established charge range prevents the need for reduced switching speed.
Solution Approach 2:
The patent changes the parameter of gate charge quantity from an uncontrolled variable to a precisely controlled parameter within a specific range. By controlling the gate charge to be between the minimum extraction charge (Qg,min) and maximum extraction charge (Qg,max), the electric field strength is maintained in an optimal range that prevents dynamic avalanche while avoiding excessive turn-off losses associated with reduced switching speed.
2Loss of energy
If the switching speed is maintained at normal levels, then the turn-off losses remain low, but high electric field strengths cause dynamic avalanche and IGBT failure
Solution Approach 1:
The patent implements feedback control by continuously monitoring the gate charge quantity and adjusting it to remain within the specified range. The control mechanism uses the relationship between gate charge and electric field strength to provide feedback that prevents the electric field from reaching levels that would cause dynamic avalanche, while allowing normal switching speed and acceptable turn-off losses.
Solution Approach 2:
The patent applies dynamics by making the gate charge control adaptive and variable rather than fixed. The gate charge is dynamically adjusted within the range defined by minimum and maximum extraction charges, allowing the system to optimize performance for different operating conditions while consistently preventing dynamic avalanche and maintaining acceptable turn-off losses.
3Reliability
If a trigger signal is used to recharge the gate at the first point in time, then transient avalanche oscillations are avoided, but the device complexity increases
Solution Approach 1:
The patent extracts the essential protective function from complex trigger signal mechanisms and implements it through direct control of the gate charge quantity. Instead of using additional trigger signals and recharge circuits, the solution focuses on precisely controlling the gate charge to remain within the safe range, thereby avoiding transient avalanche oscillations without requiring complex additional circuitry.
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
Prevents dynamic avalanche during IGBT switching off without increasing switch-off losses, by precisely controlling the charge extraction to maintain the IGBT's ability to handle maximum stationary blocking voltage.
Implementation Method 1
When an IGBT is switched off, high electric field strengths occur in the IGBT, which can lead to dynamic avalanche
Implementation Method 2
While the turn-off voltage is being applied, a gate current flowing in the gate is measured, a charge removed from the gate is determined from the gate current
Data Source
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AI summary
The invention relates to a method for operating an IGBT (1, 2), wherein a maximum stationary reverse bias required for operation of the IGBT (1, 2) is determined, a first removal charge is determined, the removal of which at the gate (5) of the IGBT (1, 2) causes an electric field strength that enables the IGBT (1, 2) to accept the maximum stationary reverse bias during stationary blocking, a second removal charge is determined, the removal of which at the gate (5) causes an electric field strength that leads to a dynamic avalanche, and, during switching off of the IGBT (1, 2), a removal charge greater than the first removal charge and less than the second removal charge is removed from the gate (5) during a charge removal duration (T3).