MOSFET Gate Drive Control for Oscillation Reduction
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Solution Overview
Problem
Conventional unipolar power semiconductor switches, such as MOSFETs, experience oscillations due to parasitic inductances and capacitances during commutation, which hinder parallel connection and electromagnetic compatibility, and their switching behavior is dependent on current direction, leading to increased switching losses and electromagnetic interference.
Innovation Solution
A method and device controlling the commutation process between two MOSFET switching modules with specific drive voltage profiles, including a first drive voltage below the threshold to turn off the first MOSFET, a second intermediate drive voltage to influence the turn-off behavior of the intrinsic diode, and a third drive voltage to turn on the second MOSFET, allowing for optimized commutation independent of current direction and reducing oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If MOSFETs are used for high switching frequency applications, then switching speed and power density are improved, but oscillations occur due to parasitic inductances and capacitances during commutation
Solution Approach 1:
The patent applies a multi-stage gate drive voltage sequence before the main switching action. A first gate drive voltage is applied to pre-charge the gate, followed by a second higher voltage to fully turn on the MOSFET. This preliminary action reduces the dV/dt stress and minimizes oscillations during commutation by controlling the turn-on rate.
Solution Approach 2:
The patent uses dynamic gate resistance adjustment during the switching process. The gate resistance is varied in different stages of the switching cycle to optimize both turn-on and turn-off behavior. This dynamic control allows fast switching while damping parasitic oscillations caused by stray inductances and capacitances.
2Device complexity
If intrinsic inverse diodes of MOSFETs are used for reverse conduction, then device complexity is reduced, but turn-off behavior is influenced by current direction leading to increased switching losses
Solution Approach 1:
The patent changes the gate drive voltage parameters based on the switching stage. Different gate voltages (first gate drive voltage below threshold, second gate drive voltage above threshold) are applied at different times to control the MOSFET and diode behavior. This parameter variation optimizes turn-off behavior and reduces switching losses regardless of current direction.
Solution Approach 2:
The patent implements periodic gate drive voltage pulses with specific timing and duration. The first gate drive voltage is applied for a first time period, followed by a second gate drive voltage for a second time period. This periodic action ensures proper commutation and minimizes reverse recovery effects.
3Power
If multiple MOSFET switching modules are connected in parallel to increase current capacity, then power handling capability is improved, but oscillations mutually influence and amplify each other
Solution Approach 1:
The patent applies preliminary gate drive voltages to all parallel MOSFETs in a coordinated manner. By pre-charging gates and controlling turn-on sequences across parallel devices, the patent ensures uniform current distribution and prevents oscillation amplification between modules.
Solution Approach 2:
The patent employs feedback control to monitor and adjust gate drive signals for parallel MOSFETs. By detecting current distribution and switching behavior, the control system adjusts gate voltages to maintain balanced operation and suppress mutual oscillation amplification.
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 reduces oscillations and switching losses, enhances electromagnetic compatibility, and enables higher switching frequencies, making the method suitable for various power converter applications by minimizing the influence of parasitic effects and improving dynamic current distribution.
Implementation Method 1
The first and the second MOSFET can be controlled by a gate-source voltage in order to be switched on, i.e. switched conductive, or switched off, i.e. switched non-conductive
Implementation Method 2
each having an intrinsic inverse diode which serves as a freewheeling diode
Data Source
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AI summary
A method and a device for controlling a commutation process of a load current between two switching modules (SM1, SM2) are disclosed, each comprising a MOSFET (Q1, Q2) that can be controlled by a gate-source voltage (UGS) and an intrinsic inverse diode (D1, D2). To reduce oscillations caused by parasitic circuit parameters during the commutation of the inverse diodes (D1, D2), after switching off one of the switching modules (SM1, SM2), the gate-source drive voltage (UGS1, UGS2) applied to this switching module (SM1, SM2) is temporarily increased again to near the threshold voltage (UTH) for switching on the MOSFET (Q1, Q2), before and while the other switching module (SM2, SM1) is switched on to commutate the current from the inverse diode (D1, D2) of one switching module (SM1, SM2) to the MOSFET (Q2, Q1) of the other switching module (SM2, SM1).