Three-Level Converter Midpoint Switching for Capacitor Overvoltage
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Solution Overview
Problem
The design of a Three Phase Three Wire Three Level Converter generates higher output voltages, requiring output capacitors with higher voltage specifications to withstand increased input voltages, leading to potential damage and increased power consumption.
Innovation Solution
A power supplying device with a switch mechanism that connects and disconnects midpoints based on input voltage levels, adjusting output voltage to maintain capacitor ratings within safe limits, thereby reducing the need for high-spec capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the input voltage increases, then the output voltage increases, but the output capacitors require higher voltage specifications leading to potential damage and increased power consumption
Solution Approach 1:
The patent applies the dynamics principle by introducing a controllable switch connected between the neutral point and the second midpoint that can dynamically change its conduction state based on input voltage levels. When the input voltage exceeds a predetermined threshold, the controller activates the switch to provide an alternative current path, thereby limiting the voltage stress on output capacitors. This dynamic adjustment allows the system to adapt to varying input conditions and protect capacitors from overvoltage damage.
2Power
If the input voltage increases, then the output voltage increases, but higher spec capacitors are required leading to increased cost and complexity
Solution Approach 1:
The patent employs the intermediary principle by introducing a switch as a mediating component between the neutral point and the second midpoint. This switch acts as a protective intermediary that redirects excess voltage away from the output capacitors when input voltage becomes excessively high. By inserting this intermediate control element, the system can maintain normal high output voltage operation while preventing dangerous voltage spikes from reaching the capacitors, thus allowing the use of lower-specification, more cost-effective capacitors.
3Object-affected harmful factors
If a midpoint connection is made to reduce common-mode noise, then electromagnetic interference is reduced, but output voltage increases requiring higher voltage capacitors
Solution Approach 1:
The patent resolves this contradiction by making the midpoint connection dynamic rather than fixed. The switch connected to the second midpoint can be controlled to conduct or block based on real-time voltage conditions. During normal operation, the switch remains non-conducting, allowing the midpoint connection to provide common-mode noise reduction. When input voltage exceeds safe levels, the switch activates to limit voltage stress on capacitors, thus maintaining both noise reduction benefits and capacitor protection.
Data Source
AI summary
A power supplying device comprises a converter circuit, configured to provide power to a load according to input power sources. The converter circuit comprises: input terminals coupled to the input power sources; a first and second output terminals coupled to the load, generating an output voltage according to the input sources; a first capacitor coupled to the first output terminal and a first midpoint; a second capacitor coupled to the second output terminal and the first midpoint; filtering capacitors coupled to the input sources and a second midpoint; a switch coupled to the first and second midpoints; and a controller controlling the switch according to an input voltage of the input terminals; wherein when the input voltage is lower than a predetermined voltage level, the switch is conducted, and when the input voltage is higher than the predetermined voltage level, the switch is not conducted.