DC Bus Capacitor Network for Differential Lightning Overstress
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Solution Overview
Problem
Photovoltaic inverters are vulnerable to differential mode lightning strikes, which cause rapid increases in bus voltage, posing a risk of voltage overstress to semiconductor devices due to insufficient protection by existing lightning protection apparatuses.
Innovation Solution
The power conversion device incorporates capacitors with varying capacitance values connected in series and parallel configurations, along with discharge units like gas discharge tubes or varistors, to divert lightning strike charges away from semiconductor devices, thereby stabilizing bus voltage during differential mode lightning strikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing lightning protection apparatus with thin film capacitors and electrolytic capacitors is used, then common mode lightning strikes are protected, but differential mode lightning strikes cause rapid bus voltage increases that can damage semiconductor devices
Solution Approach 1:
The capacitor bank is segmented into multiple parallel branches, each containing series-connected thin film capacitors and electrolytic capacitors. This segmentation allows differential mode lightning strike current to be distributed across multiple paths, preventing rapid voltage buildup on the bus while maintaining common mode protection capabilities.
Solution Approach 2:
The patent introduces discharge units (such as gas discharge tubes or varistors) as intermediary components connected in parallel with the inductor. These intermediaries provide an alternative path for lightning strike current, diverting it away from the bus capacitor and preventing voltage overstress on semiconductor devices during differential mode strikes.
2Illumination intensity
If thin film capacitors with small capacitance values are used to absorb high-frequency ripples, then high-frequency noise is filtered, but differential mode lightning strike current causes rapid bus voltage increases
Solution Approach 1:
The capacitor system is divided into multiple parallel branches with series-connected capacitors. This segmentation increases the overall capacitance value presented to differential mode lightning strike current, reducing the rate of voltage change (di/dt) while maintaining high-frequency ripple absorption capabilities through the thin film capacitor segments.
Solution Approach 2:
Discharge units are introduced as intermediary components that activate during differential mode lightning strikes. These units provide an alternative current path, preventing the full lightning strike current from charging the thin film capacitors rapidly, thereby stabilizing bus voltage while allowing the thin film capacitors to continue their high-frequency filtering function.
3Reliability
If electrolytic capacitors are connected in series to decoupling inductors, then high-frequency ripples are prevented from flowing into electrolytic capacitors, but differential mode lightning strike current flows into thin film capacitors causing voltage increase
Solution Approach 1:
The capacitor bank is segmented into multiple parallel branches, each containing series-connected thin film and electrolytic capacitors. This segmentation ensures that during differential mode lightning strikes, the current is distributed across multiple paths with higher total capacitance, reducing voltage buildup while maintaining the series connection protection for electrolytic capacitors against high-frequency ripples.
Solution Approach 2:
Discharge units are introduced as intermediary components connected in parallel with the inductor. These units provide an alternative path for differential mode lightning strike current, preventing it from flowing into the thin film capacitors and causing rapid voltage increases, while the series connection between inductor and electrolytic capacitors continues to protect against high-frequency ripple injection.
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
Effectively prevents rapid bus voltage increases, safeguarding semiconductor devices from voltage overstress by efficiently dissipating lightning strike energy through capacitors with larger capacitance values, ensuring device stability and safety.
Implementation Method 1
The power conversion device includes a first capacitor C11, a second capacitor C21, a first inductor L1, and a first discharge unit. The second capacitor C21 is connected in series to the first inductor L1 and then connected in parallel to the first capacitor C11, where a capacitance value of the second capacitor C21 is greater than a capacitance value of the first capacitor C11.
Implementation Method 2
The power conversion device incorporates capacitors with varying capacitance values connected in series and parallel configurations, along with discharge units like gas discharge tubes or varistors, to divert lightning strike charges away from semiconductor devices
Data Source
AI summary
A power conversion device includes a positive direct current bus, a negative direct current bus, a first capacitor, a second capacitor, a first inductor, a first discharge unit. The first capacitor is connected between the positive direct current bus and the negative direct current bus. The second capacitor is connected in series to the first inductor and then connected in parallel to the first capacitor, where a capacitance value of the second capacitor is greater than a capacitance value of the first capacitor. The first discharge unit is connected in parallel to the first inductor, and is configured to be in a conducted state when a voltage of the first inductor is greater than a first action voltage threshold. In the embodiments, a case in which a semiconductor device in the power conversion device has a risk of voltage overstress caused by a differential mode lightning strike can be avoided.