Power Semiconductor Switch Turn-Off Control for Overvoltage Limiting
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Solution Overview
Problem
Power semiconductor switches experience overvoltages during switching off due to stray inductances, leading to potential damage, especially at high load currents, and reducing switching speed to mitigate this increases energy losses and reduces efficiency.
Innovation Solution
A control device for power semiconductor switches that includes a current detection circuit and an actuating device to generate a reduced actuating voltage during switching off, prolonging the time interval between the initial and 10% of the initial voltage value by at least 10% when a high-current signal is present, thereby reducing the rate of current variation and minimizing overvoltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching off speed of the power semiconductor switch is increased, then the electrical efficiency is improved, but overvoltages occur between the load current terminals which can damage the switch
Solution Approach 1:
The control device dynamically adjusts the actuating voltage based on the detected load current. When high load current is detected, the control device reduces the actuating voltage during switching off, which prolongs the switching off time and reduces the rate of current variation, thereby limiting overvoltages. This dynamic adaptation allows the system to optimize between efficiency and overvoltage protection based on real-time operating conditions.
Solution Approach 2:
The invention changes the actuating voltage parameter from a fixed value to a variable value that depends on the load current. The control device detects the load current and accordingly adjusts the actuating voltage applied to the power semiconductor switch during switching off. This parameter change enables the system to reduce switching speed (and thus overvoltages) only when necessary, rather than maintaining a consistently slow switching speed.
2Object-affected harmful factors
If the switching off speed is reduced to reduce overvoltages, then overvoltages are minimized, but energy losses increase and electrical efficiency decreases
Solution Approach 1:
The control device dynamically adapts the switching off speed to the actual operating conditions by detecting the load current. When the load current is high, the device slows down the switching off process to limit overvoltages. When the load current is normal, the device maintains a normal switching off speed to ensure efficiency. This dynamic behavior eliminates the need for a consistently slow switching speed, thereby minimizing energy losses while still providing overvoltage protection when needed.
Solution Approach 2:
The actuating voltage parameter is changed from a static value to a dynamic value that varies with load current. The control device modifies the actuating voltage during switching off based on the detected current level, which in turn adjusts the switching off speed. This parameter change enables the system to achieve slow switching off (and thus overvoltage reduction) only under high current conditions, rather than under all operating conditions, thereby preserving efficiency during normal operation.
3Object-affected harmful factors
If monitoring and control circuitry is added to detect high current and adjust actuating voltage, then overvoltages are reduced, but device complexity increases
Solution Approach 1:
The control device incorporates a feedback mechanism where the load current is detected and used to adjust the actuating voltage during switching off. The control device monitors the actual operating conditions and accordingly modifies the control signal applied to the power semiconductor switch. This feedback approach enables the system to automatically adapt to different operating conditions and provide overvoltage protection only when necessary, without requiring complex external control systems.
Solution Approach 2:
The control device performs self-monitoring and self-adjustment by detecting its own operating conditions (load current) and automatically adjusting the actuating voltage accordingly. The control device does not require external complex control systems but rather uses built-in detection and control capabilities to manage the switching process. This self-service approach minimizes the need for additional complex external circuitry while still achieving overvoltage protection.
Data Source
AI summary
A control device for a power semiconductor switch includes an actuating device, which on a third control device terminal, upon the reception of a switching on command, generates an actuating voltage for the switching on of the power semiconductor switch and, upon the reception of an switching off command, generates an actuating voltage for the switching off of the power semiconductor switch, and a current detection circuit, which generates a first high-current signal if an actuating voltage assumes a voltage value at which the power semiconductor switch is switched on, and a primary voltage of the power semiconductor switch applied between first and second control device terminals exceeds a first power semiconductor switch primary voltage value. The actuating device, upon the reception of an switching off command, generates an actuating voltage for the switching off of the power semiconductor switch, such that the actuating voltage is reduced such that the time interval elapsing between a first actuating voltage value, assumed by the actuating voltage upon the reception of the switching off command, and the achievement of a second actuating voltage value of the actuating voltage, which is equal to 10% of the first actuating voltage value, is greater in the presence of the first high-current signal than in the absence of the first high-current signal.