Active Gate Trajectory Control for Zero-Overshoot Switching
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Solution Overview
Problem
High switching speeds in power converters using wide-band gap devices lead to voltage overshoots and increased switching losses, as well as electromagnetic interference (EMI) due to layout stray inductance, which stress transistors and reduce efficiency.
Innovation Solution
A device and method for controlling the switching of power semiconductor switches using an active gate drive circuit with feedback signals to manage switching transitions, employing two threshold values to adjust the switching trajectory and minimize overshoots, allowing for fast switching with reduced ringing during turn-on and turn-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If high switching speed is used, then switching losses are reduced, but voltage overshoot increases
Solution Approach 1:
The switching transition is divided into multiple stages with different damping levels. During the early phase of switching, minimal damping is applied to maintain fast transition and low losses. During the late phase when voltage approaches the final value, increased damping is applied to suppress overshoot and ringing. This segmentation of the switching process allows simultaneous optimization of both switching speed and overshoot control.
Solution Approach 2:
The gate driver impedance is dynamically adjusted during the switching transition rather than being fixed. The damping factor changes as a function of the voltage transition progress, providing low damping during the main switching event for fast transition, and high damping near the end of transition to eliminate overshoot. This dynamic adaptation resolves the contradiction between fast switching and overshoot suppression.
2Productivity
If high switching speed is used, then productivity is improved, but electromagnetic interference increases
Solution Approach 1:
The parasitic inductance in the circuit layout, which normally causes harmful voltage overshoots and EMI during fast switching, is converted into a beneficial damping element. By carefully controlling the gate voltage waveform and utilizing the natural damping effect of the circuit inductance during the tail end of switching, the parasitic elements become part of the solution rather than the problem, allowing fast switching with reduced EMI.
Solution Approach 2:
The gate driver preemptively shapes the voltage waveform to prevent the conditions that lead to EMI. By controlling the rate of change of voltage and current during switching, and by applying increased damping before overshoot can occur, the system prevents the generation of high-frequency noise and electromagnetic interference, allowing high switching frequencies without EMI problems.
3Object-affected harmful factors
If switching transition is slowed down, then voltage overshoot is reduced, but switching losses increase
Solution Approach 1:
The damping applied during switching is periodic in nature, being activated only during specific phases of the voltage transition. The gate driver applies minimal or no damping during the main switching event when speed is critical, then activates strong damping only during the final phase of transition when the voltage is close to its final value. This periodic application of damping eliminates overshoot without affecting the main switching speed or increasing losses.
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
This approach enables high-speed switching with low voltage overshoot and minimized switching losses by slowing down transitions only when necessary, maximizing commutation speed and reducing EMI, thus enhancing the performance and reliability of power converters.
Implementation Method 1
a feedback circuit (202) sensing the drain to source voltage of the power semiconductor switch and generating a feedback signal having a value being proportional to a derivative of the voltage
Data Source
Figure 1a~1c
Figure 2
Figure 3
AI summary
The present invention concerns a device for controlling the switching from a conducting state to a non conducting state or from a non conducting state to a conducting state of at least one semiconductor power switch providing current to a load, the device receiving an input signal that is intended to drive the semiconductor power switch. The device: - determines a first and a second thresholds from power supplies values, - senses the drain to source voltage of the semiconductor power switch when the semiconductor power switch switches, - compares, during the switching, the drain to source voltage to the first or the second threshold value, - combines the input signal to a voltage that is representative of the derivative of the drain to source voltage if the drain to source voltage is upper than the first or the second threshold value.