Smoothing Capacitor Short-Circuit Detection in Power Converters
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Solution Overview
Problem
Existing power conversion equipment with high-voltage and large-capacitor configurations face challenges in reliably detecting capacitor failures, especially when capacitors are connected in series and parallel, as the voltage variation becomes small and detection becomes difficult, especially when the number of series-connected capacitors is not a multiple of 2 or when capacitors are connected to ground, leading to potential undetected failures and increased complexity.
Innovation Solution
A power conversion equipment with a capacitor failure detecting circuit that includes N switch circuits, N exciting resistors, and N contact resistors, where each switch circuit is connected to capacitors in series, allowing for reliable detection of short-circuit failures by monitoring the voltage between contact resistors, even when capacitors are connected in series and parallel, and handling configurations where capacitors are connected to ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a diode bridge circuit with level detector is used to detect capacitor failures, then the detection circuit becomes simpler and can handle large numbers of capacitors, but the detection becomes unreliable when the number of series-connected capacitors is not a multiple of 2 or when voltage variation is small
Solution Approach 1:
The detection circuit is segmented into multiple independent switch circuits (first switch circuit, second switch circuit, etc.), each corresponding to a specific capacitor. This segmentation allows each switch circuit to independently detect the status of its associated capacitor through voltage detection at specific nodes, avoiding the reliability issues of unified detection methods while maintaining circuit simplicity.
Solution Approach 2:
Switch circuits act as intermediary components between the capacitors and the detection mechanism. Each switch circuit includes switching elements (transistors) that are controlled based on voltage conditions at intermediate nodes (e.g., node A1, node A2). This intermediary approach enables reliable detection by translating subtle voltage variations into detectable switching actions, solving the problem of small voltage variation detection.
2Reliability
If individual voltage monitoring circuits are provided for each capacitor, then capacitor failure detection reliability is improved, but the detection circuit becomes complicated
Solution Approach 1:
Multiple switch circuits share common structural components and detection mechanisms. Each switch circuit follows the same design pattern with switching elements, resistors, and voltage detection nodes, allowing the system to maintain high detection reliability while avoiding the complexity of completely independent circuits. The universal structure enables reliable individual capacitor monitoring through standardized, repeatable units.
Solution Approach 2:
The detection circuits are merged at multiple levels: switching elements from different switch circuits share common control nodes and voltage reference points; resistors are shared between adjacent switch circuits; and the overall detection logic is unified through common detection nodes (e.g., node B1, node B2). This merging reduces component count and circuit complexity while preserving individual capacitor detection capability.
3Power
If capacitors are connected in series and parallel configurations, then the power conversion equipment can handle higher voltages and capacities, but the detection of individual capacitor failures becomes more difficult due to small voltage variations
Solution Approach 1:
The detection approach applies local quality by creating distinct detection zones at specific nodes within the capacitor array. Each switch circuit monitors local voltage conditions at its associated capacitor terminals (e.g., node A1 for first capacitor, node A2 for second capacitor). This localized detection approach enables reliable failure identification in high-voltage series-parallel configurations where overall voltage variations are small, as each local node provides sensitive indication of its corresponding capacitor's status.
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 enables high-reliability detection of capacitor failures in a relatively simple circuit, preventing further damage by identifying short-circuit failures among capacitors connected in series and parallel, even in complex configurations, ensuring the equipment's operational safety.
Implementation Method 1
an exciting current flows to the exciting circuit of the first switch circuit 7SW1, and the contact 7MS of the first switch circuit 7SW1 is closed
Implementation Method 2
a diode 10D1 is connected in a direction for flowing current from the first connecting point to a high potential side of the second capacitor 4C2
Data Source
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AI summary
To provide a power conversion equipment which can detect short circuit failure of series connected capacitors of a smoothing capacitor circuit 4. A capacitor failure detecting circuit is composed of the combination of switch units 7SW, exciting resistors 8R, contact resistors 9R, and diodes 10D. The switch unit 7SW is provided with an exciting circuit and a contact circuit, and when a predetermined current flows through the exciting circuit the contact circuit is closed. The exciting circuit of the switch unit 7SW and the exciting resistor 8R are alternately connected in series, and the contact circuit and the contact resistor 9R are alternately connected in series, corresponding to the number of the series connected capacitors, and these series circuits are connected in parallel with the capacitors. A connecting point of the exciting resistor 8R and a next switch unit and a connecting point of the contact resistor 9R the next switch unit are connected, and the diode 10D is connected from this point to a connecting point corresponding to the capacitor. When the excitation of the switch circuit 7SW having a lowest potential is turned OFF, it is judged that at least one of the series connected capacitors has failed by short circuit.