Off-Voltage Control Circuit for Power Conversion Short-Circuit Prevention
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Solution Overview
Problem
Conventional power conversion circuits face issues with short-circuiting due to high dv/dt applications, leading to premature deterioration of switching elements and reduced reliability, as they require prolonged application of negative bias voltage, which lacks versatility and cannot adapt to changing operational conditions.
Innovation Solution
A power conversion circuit that limits the application of negative bias voltage to an extremely short duration during the transition periods between upper and lower arm operations, using advanced gate drive circuits with detection mechanisms for main terminal voltages, currents, and control terminal voltages to minimize the duration of low off-voltage application, thereby preventing short-circuiting and extending the life of switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If negative bias voltage is applied to the control terminal of a switching element during off state to prevent simultaneous conduction, then short-circuiting is avoided, but the duration of low off-voltage application is prolonged causing premature deterioration of the switching element
Solution Approach 1:
The gate drive circuit dynamically adjusts the off-voltage level based on the operational state of switching elements. During transition periods when one arm is turning off and the other is turning on, the circuit applies a first off-voltage (e.g., -15V) to prevent simultaneous conduction. After the transition period ends, the circuit switches to a second off-voltage (e.g., -5V) that is less detrimental to the switching element. This dynamic voltage adjustment maintains reliability during critical periods while reducing stress during stable periods.
Solution Approach 2:
The invention changes the voltage parameter of the off-state gate drive signal based on timing conditions. The gate drive circuit uses detection mechanisms to monitor the operational state of switching elements and adjusts the off-voltage magnitude accordingly. By varying the voltage parameter from a higher magnitude during transitions to a lower magnitude during stable states, the circuit prevents short-circuiting while minimizing deterioration of the switching element.
2Device complexity
If conventional gate drive circuits use fixed negative bias voltage during entire off period, then simplicity is maintained, but versatility and adaptability to changing operational conditions are reduced
Solution Approach 1:
The gate drive circuit incorporates feedback mechanisms that detect the operational state of switching elements (such as drain-source voltage or gate-source voltage levels) and use this information to control the off-voltage output. The detection unit monitors parameters like the voltage across the switching element or the state of the other arm, and the control unit adjusts the off-voltage accordingly. This feedback-based approach enables the circuit to adapt to changing operational conditions while maintaining a relatively simple overall structure.
Solution Approach 2:
The gate drive circuit automatically adjusts its own output voltage based on detected operational conditions without requiring external intervention. The detection and control units work together to autonomously determine when to apply different off-voltage levels, making the circuit self-adaptive to operational changes. This self-service capability enhances versatility while avoiding the need for complex external control systems.
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
The solution effectively prevents short-circuiting and enhances the reliability and lifespan of switching elements by minimizing the duration of low off-voltage application, adapting to changing operational conditions, and optimizing the off-voltage based on detected parameters.
Implementation Method 1
an off-voltage control circuit controls an output voltage of a lower-arm gate drive power supply in response to a voltage adjustment signal from a signal output circuit to generate a second voltage lower than a first voltage satisfying an off state of the lower arm during a time period from termination of turn-off operation of the lower arm until start of turn-on operation of the upper arm
Implementation Method 2
A parasitic capacitance 200 of the lower arm 22u is rapidly charged according to the switching speed of the upper arm 21u, causing flow of a current Ig via a lower-arm gate resistance 104u and a lower-arm arm-drive circuit 102u
Data Source
AI summary
In a power conversion circuit operating with high frequency, an off-voltage control circuit 101u of a lower-arm gate drive circuit 24u controls the output voltage of a gate drive power supply 103u to change the output voltage to a voltage lower than a predetermined off voltage during a time period from termination of turn-off operation of a lower arm 22u until start of turn-on operation of an upper arm 21u, and thereafter return the output voltage to the predetermined off voltage immediately after termination of the turn-on operation of the upper arm 21u. With this control, short-circuiting through the upper and lower arms occurring due to a high voltage change dv/dt can be avoided, and the life of a switching element constituting the power conversion circuit improves, increasing the reliability of the power conversion circuit.