Bridge Circuit Switch-Off Sequencing to Prevent Switch Overvoltage
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Solution Overview
Problem
In bridge circuits, simultaneous switching off of power semiconductor switches can lead to higher voltages being applied to individual switches due to differing switching speeds, potentially causing damage, especially when using switches of different technologies.
Innovation Solution
A method where the fifth and sixth power semiconductor switches are simultaneously switched on while the first and fourth are switched off, permanently clamping the intermediate points to the neutral connection's potential, preventing voltage floating and ensuring no higher voltages than normal operation are applied during the switch-off process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If all power semiconductor switches are simultaneously controlled to be transferred to a switched-off state, then the shutdown process is fast and simple, but higher voltages than during normal operation are temporarily applied to individual switches due to different switching speeds
Solution Approach 1:
The patent segments the simultaneous switch-off action into sequential phases: first switching off switches T1 and T4, then after a predetermined time delay, switching off switches T2 and T3. This temporal segmentation prevents voltage floating and overvoltage conditions that would occur with truly simultaneous switching, while still achieving rapid shutdown.
Solution Approach 2:
The patent performs preliminary action by switching off switches T1 and T4 before switching off switches T2 and T3. This preliminary sequencing ensures that the bridge circuit is placed in a safe state first, preventing overvoltage conditions before they can occur, while maintaining overall fast shutdown performance.
2Adaptability or versatility
If power semiconductor switches of different technologies are used in the bridge circuit, then design flexibility and optimization are improved, but individual switches transfer to switched-off state at different speeds causing voltage imbalances
Solution Approach 1:
The patent divides the switch-off process into two distinct temporal groups: first group (T1, T4) and second group (T2, T3). This segmentation compensates for different switching speeds of various semiconductor technologies by ensuring that slower switches are not forced to switch simultaneously with faster ones, preventing voltage imbalances while allowing design flexibility.
Solution Approach 2:
The patent incorporates a control unit that monitors the switching states and uses feedback control to manage the sequential switch-off process. The control unit ensures that switches are switched off in the correct sequence with appropriate time delays, accommodating different technologies while maintaining voltage balance and reliability.
3Power
If the bridge circuit uses a multi-level topology with neutral connection, then voltage distribution during normal operation is optimized, but during simultaneous switch-off voltage floating occurs at intermediate points
Solution Approach 1:
The patent performs preliminary action by switching off switches T1 and T4 (connected to DC voltage connections) before switching off switches T2 and T3 (connected to AC output). This preliminary sequencing prevents voltage floating at intermediate points by establishing a defined voltage path through the neutral connection before disconnecting the AC-side switches.
Solution Approach 2:
The patent uses the neutral connection as an intermediary element that provides a stable reference potential during the sequential switch-off process. By maintaining connection to the neutral point during the transition, the circuit prevents voltage floating at intermediate points while allowing optimized voltage distribution characteristic of multi-level topologies.
Data Source
AI summary
A method for switching off power semiconductor switches in a bridge circuit having first through sixth power semiconductor switches. The method includes a switch-off process for establishing a final switch configuration in which all power semiconductor switches in the bridge circuit are in a switched-off state. Over the course of the switch-off process, a switch configuration is established in which the fifth power semiconductor switch and the sixth power semiconductor switch are concurrently in a switched-on state, while the first power semiconductor switch and the fourth power semiconductor switch are in a switched-off state. Also disclosed is a bridge circuit having a control circuit configured to carry out such a method. In addition, an inverter that includes at least one bridge circuit of this type is also provided.