Converter Control Method for Reducing Parasitic Diode Thermal Stress
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Solution Overview
Problem
Traditional power conversion circuits face significant power loss and thermal stress due to reverse current flowing through parasitic diodes during scram events, leading to potential damage, and existing solutions either increase costs or enhance protection circuit requirements.
Innovation Solution
A control method and device that detect the direction of inductor current in a conversion circuit, selectively turning on and off upper and lower semiconductor switches to direct freewheel current away from parasitic diodes, thereby preventing reverse current flow and reducing thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper switch and lower switch are turned off no matter what the direction of current is during a scram event, then the protection response is simple and fast, but the parasitic reverse diode suffers from large power loss and thermal stress
Solution Approach 1:
The patent applies dynamic control by detecting the direction of inductor current during scram events and selectively turning on either the upper or lower switch based on current direction. This dynamic response replaces the static approach of always turning off both switches, thereby directing freewheel current away from parasitic diodes and reducing power loss while maintaining fast protection response.
Solution Approach 2:
The patent changes the control parameter from a fixed state (both switches off) to a variable state (selective switch on/off based on current direction). By monitoring current direction and adjusting switch states accordingly, the system optimizes the balance between protection speed and power loss reduction during scram events.
2Reliability
If a high-performance diode is connected in parallel to the switch to conduct reverse current, then the parasitic diode is protected from thermal stress, but material cost and manufacturing cost increase
Solution Approach 1:
The patent enables the existing semiconductor switches to protect themselves by using their own body diodes in a controlled manner. Through intelligent control that directs current away from parasitic diodes during scram events, the system eliminates the need for external protection diodes, thereby reducing material costs and manufacturing complexity while maintaining reliability.
Solution Approach 2:
The control circuit acts as an intermediary that manages current flow during scram events. By detecting current direction and selectively activating switches, the control circuit mediates between the inductor and parasitic diodes, preventing harmful reverse current flow without requiring additional physical protection components.
3Reliability
If a semiconductor switch with larger current specification is used with a highly sensitive protective detection circuit, then severe overcurrent or overheat is avoided, but the requirements for protection and detection circuits are enhanced and costs increase
Solution Approach 1:
The patent applies partial action by implementing protection only when necessary (during scram events with reverse current flow). Instead of using oversized switches and highly sensitive detection circuits continuously, the system activates selective switch control only when scram conditions are detected, thereby reducing overall system complexity and cost while maintaining adequate protection.
Solution Approach 2:
The protection system transitions from a static oversized design to a dynamic adaptive design. The control circuit dynamically adjusts switch states based on real-time current direction detection during scram events, providing adequate protection without requiring continuously oversized components or highly sensitive detection circuits.
Data Source
AI summary
A control method, which is applied to a conversion circuit including at least one bridge arm and an inductor, the bridge arm including an upper semiconductor switch and a lower semiconductor switch connected in series, and one end of the inductor being connected to a midpoint of the bridge arm, includes: detecting a direction of current of the inductor when a scram event occurs in the conversion circuit; turning on the upper semiconductor switch and turning off the lower semiconductor switch when the direction of current of the inductor is a first direction, wherein the first direction is the direction when the current flows from one end of the inductor to the midpoint of the bridge arm; and turning off the upper semiconductor switch and turning on the lower semiconductor switch when the direction of current of the inductor is a second direction.