Multilevel DC-DC Converter Discharge Circuit for Overvoltage Control
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Solution Overview
Problem
Multilevel DC-DC converters experience overvoltage issues after protective stoppage, leading to repeated shutdowns due to charging of filter capacitors, which causes overvoltage on the secondary side, resulting in ineffective restarts.
Innovation Solution
A multilevel power conversion device with primary-side and secondary-side filter capacitors, a power converter featuring switching elements, freewheel diodes, and snubber resistances, along with a discharge circuit and controller to manage voltage by discharging the capacitors after stoppage, preventing overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the multilevel DC-DC converter performs protective stoppage to prevent overvoltage, then the immediate overvoltage is prevented, but the filter capacitors charge through the snubber resistance after stoppage, causing repeated overvoltage and shutdowns
Solution Approach 1:
The control device detects converter stoppage and actively discharges the filter capacitors through the discharge circuit before normal operation resumes, preventing the harmful charging effect that would otherwise occur through the snubber resistance during the idle period
Solution Approach 2:
A discharge circuit with discharge resistance is introduced as an intermediary component to provide a controlled discharge path for the filter capacitors, replacing the uncontrolled charging path through the snubber resistance and preventing overvoltage generation
2Productivity
If the converter is restarted after protective stoppage, then normal operation should resume, but the charged filter capacitors cause immediate overvoltage leading to another shutdown
Solution Approach 1:
The control device executes capacitor discharge operation whenever stoppage is detected, ensuring the capacitors are in a safe state before restart, thereby eliminating the condition that causes repeated shutdowns and improving operational continuity
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 solution effectively suppresses overvoltage by discharging primary-side and secondary-side filter capacitors after stoppage, ensuring stable operation and preventing repeated shutdowns of the DC-DC converter.
Implementation Method 1
a discharge circuit connected in parallel to the plurality of primary side filter capacitors or the secondary-side filter capacitor... The controller, by causing the discharge to operate circuit after stoppage of the power converter, discharges the plurality of primary-side filter capacitors or the secondary-side filter capacitor
Implementation Method 2
a plurality of snubber resistances, each snubber resistance of the plurality of snubber resistances connected in parallel to one of the plurality of switching elements
Data Source
AI summary
A power converter has: switching elements connected in parallel to each of primary-side filter capacitors, freewheel diodes connected in parallel to the switching elements, and snubber resistances connected in parallel to the switching elements. The controller causes stoppage of the power converter by turning off each of the switching elements. After stoppage of the power converter, the controller causes a discharge circuit to operate by turning on a thyristor, thereby discharging the primary-side filter capacitors. By discharging of the primary-side filter capacitors, a secondary-side filter capacitor is discharged via the freewheel diodes.