Flying capacitor-type NPC three-level topology
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Solution Overview
Problem
The NPC three-level topology lacks effective protection against short circuits, leading to potential damage to switches due to overvoltage, resulting in low safety and reliability of the circuit.
Innovation Solution
Incorporating a flying capacitor with greater than or equal to a preset capacitance into the NPC three-level topology, which clamps the inner switches and prevents overvoltage, along with a short circuit detection and control system to immediately switch off faulty switches, thereby enhancing safety and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If NPC three-level topology is used to reduce voltage stress on switches, then voltage stress is reduced to half of input voltage, but the topology cannot effectively protect against short circuits and inner switches may be damaged due to overvoltage
Solution Approach 1:
The patent introduces a flying capacitor as an intermediary component between the DC bus and the AC output. This flying capacitor acts as a mediator that limits the voltage stress on inner switches during short circuit conditions. When a short circuit occurs, the flying capacitor prevents the full DC bus voltage from appearing across the inner switches, thereby providing overvoltage protection while maintaining the voltage-stress-reduction benefit of the NPC topology during normal operation.
2Stress or pressure
If switching pattern is used to ensure voltage across inner switches does not exceed Vin/2, then voltage is controlled during normal operation, but the pattern is destroyed during short circuit and inner switches cannot be switched off immediately
Solution Approach 1:
The patent implements preliminary protection action by pre-configuring the flying capacitor in the circuit before short circuit occurs. The flying capacitor is already in place and charged to half the DC bus voltage, so when a short circuit occurs, it immediately begins to limit the voltage stress on inner switches without requiring any switching pattern changes or detection delays. This preliminary configuration enables instantaneous protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The flying capacitor topology effectively reduces the risk of switch damage from overvoltage during short circuits, improving the overall safety and reliability of the circuit by ensuring immediate switch-off and voltage management.
Implementation Method 1
a flying capacitor Css, wherein a capacitance of the flying capacitor Css is greater than or equal to a preset value
Data Source
AI summary
A flying capacitor-type NPC three-level topology, comprising: two half-busbar capacitors and at least one bridge arm. The bridge arm comprises: a flying capacitor, two inner transistor units, two outer transistor units, and two clamping diodes, wherein the capacitance of the flying capacitor is greater than a specific value. Since the flying capacitor has a clamping effect on the two inner transistor units and the capacitance of the flying capacitor is large, voltage fluctuations of the flying capacitor would not cause overvoltage of switching transistors no matter what type of short circuit fault occurs, thereby preventing the switching transistor units from being damaged due to overvoltage and further improving the security of a circuit.