Voltage Balancing in Series IGBTs Using Impedance Diverters
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Solution Overview
Problem
Existing methods for voltage balancing in series connected power switching devices, such as IGBTs, face challenges in maintaining accurate voltage sharing during static and dynamic states, especially due to parameter imbalances and high-frequency switching requirements, which can lead to power loss and component inefficiencies.
Innovation Solution
The method involves using diverters with controllable impedance to manage current imbalances during the OFF period of power switching devices, transitioning through successively higher impedance states to minimize voltage imbalances and improve static and dynamic voltage balancing, while also allowing for synchronized control and reduced power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage balancing resistors or capacitance devices are used in parallel with power switching devices, then voltage sharing is improved, but device complexity and power loss increase
Solution Approach 1:
The patent extracts the voltage balancing function from traditional parallel resistors/capacitance devices and implements it through a control circuit that actively manages voltage distribution across series-connected IGBTs. This removes the need for additional passive balancing components while maintaining voltage sharing reliability.
Solution Approach 2:
The patent employs feedback control circuits that continuously monitor voltage across each IGBT and adjust switching timing accordingly. This active feedback mechanism replaces passive voltage balancing components, reducing circuit complexity while improving voltage sharing through real-time adjustment.
2Reliability
If feedback control schemes are used for voltage balancing, then voltage sharing is improved, but device complexity and cost increase
Solution Approach 1:
The control circuit performs multiple functions simultaneously: it manages voltage balancing, synchronizes switching operations, and provides overvoltage protection. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby reducing overall device complexity while maintaining high voltage balancing accuracy.
3Reliability
If IGBTs are switched synchronously, then dynamic voltage sharing is improved, but control precision requirements increase
Solution Approach 1:
The control circuit predicts potential voltage imbalances before they occur and pre-adjusts switching timing to prevent synchronization issues. This preliminary action approach reduces the precision requirements for real-time switching synchronization while maintaining dynamic voltage sharing reliability.
4Productivity
If switching speed is increased, then productivity is improved, but voltage balancing accuracy deteriorates
Solution Approach 1:
The control circuit dynamically adjusts switching timing and impedance based on real-time voltage conditions. This dynamic adaptation allows the system to maintain high switching frequencies while preserving voltage balancing accuracy by continuously optimizing control parameters rather than relying on fixed timing.
Data Source
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AI summary
A method for voltage balancing series-connected power switching devices (IGBTs) each connected in parallel with a respective diverter having controllable impedance to controllably conduct current diverted from the associated power switching device, the method comprising the step of controlling each diverter to follow a series of at least two successively higher impedance states during an OFF period of the power switching devices. The series of impedance states for each diverter comprises a first impedance and then a second, higher impedance, the first impedance occurring in response to an indication of a start of the OFF period. The first impedance state preferably occurs during a tail current of the power switching device in parallel with the respective diverter and the second or later impedance state during a leakage current of that power switching device.