Power Converter Fault Control via Current Direction Switching
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Solution Overview
Problem
Power electronic converters face limitations in managing short circuits, as traditional methods lead to excessive loading of freewheeling diodes, necessitating over-dimensioning and increased risk of input fuse burnout.
Innovation Solution
A controller system that recognizes current direction during a short circuit and strategically switches high-leg and low-leg controllable switches to distribute fault currents, ensuring that maximum allowable I2t values of both freewheeling diodes and switches are not exceeded, thereby preventing input fuse burnout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the controllable switches are kept in a non-conductive state during a short circuit, then the freewheeling diodes can handle the short circuit currents, but the I2t values of the freewheeling diodes exceed their maximum allowable values, leading to over-dimensioning requirements
Solution Approach 1:
The patent introduces controllable switches as intermediary elements between the short circuit fault and the freewheeling diodes. During a short circuit, these switches are activated to divert current away from the freewheeling diodes, thereby protecting them from excessive I2t values. The switches act as a mediator that redistributes the fault current through alternative paths, preventing the diodes from bearing the full burden of short circuit currents.
Solution Approach 2:
The patent employs dynamic switching control where the state of controllable switches changes based on the detected fault condition. Upon detecting a short circuit, the control system dynamically transitions the switches from their normal operating state to a fault-handling state, enabling real-time adaptation to protect the freewheeling diodes. This dynamic response allows the system to optimize current distribution during transient fault conditions.
2Reliability
If the freewheeling diodes are dimensioned to handle maximum short circuit currents, then they can protect against short circuits, but the device complexity and cost increase due to over-dimensioning
Solution Approach 1:
The controllable switches serve as protective intermediaries that reduce the burden on freewheeling diodes during short circuits. By introducing this additional control layer, the system can use smaller, less expensive diodes that don't need to be over-dimensioned for extreme fault conditions, as the switches will actively manage current distribution to keep diode stress within acceptable limits.
Solution Approach 2:
The patent changes the operational parameters of the power converter system by introducing controlled switching during fault conditions. This allows the freewheeling diodes to operate within their rated parameters even during short circuits, eliminating the need for over-dimensioning. The parameter change involves transitioning from passive diode-based fault handling to active switch-controlled current management.
3Reliability
If the controllable switches are used to distribute fault currents, then the I2t values of freewheeling diodes are reduced, but the control system complexity increases
Solution Approach 1:
The patent implements a feedback-based control mechanism where the control system monitors fault conditions and adjusts the switching state of controllable switches accordingly. When a short circuit is detected, the control system receives feedback about the fault condition and automatically activates the appropriate switches to distribute current. This closed-loop feedback approach enables intelligent current management without requiring overly complex control logic, as the system responds automatically to detected fault states.
Solution Approach 2:
The control system performs self-service by automatically detecting short circuit conditions and managing its own protective response. Upon fault detection, the system autonomously activates the controllable switches to protect the freewheeling diodes without requiring external intervention or complex decision-making algorithms. This self-service capability simplifies the overall control architecture while achieving effective fault protection.
Data Source
AI summary
A controller (203) comprises a processing system (205) for controlling a power electronic converter during a short circuit taking place in a direct voltage side of the power electronic converter. The processing system recognizes a direction of current in a phase (126-128) of an alternating voltage side of the power electronic converter, sets a high-leg controllable switch (108-110) of the phase to a conductive state while keeping a low-leg controllable switch (111-113) of the phase in a non-conductive state when the recognized direction of the current is outwards from the power electronic converter, and otherwise sets the low-leg controllable switch to the conductive state while keeping the high-leg controllable switch in the non-conductive state. Thermal loadings of freewheeling diodes (114-119) of the power electronic converter are reduced since currents needed to burn input fuses (122) of the power electronic converter are shared between the controllable switches and the freewheeling diodes.