Capacitive Ground Fault Detection Circuit for Marine Power Systems
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Solution Overview
Problem
Existing power conversion systems face challenges in detecting and identifying high resistance ground faults due to high leakage current and common mode noise, particularly in marine applications where resistive dividers fail to meet isolation requirements and chassis-referenced sensing circuits suffer from high leakage current.
Innovation Solution
A low leakage sensing circuit with a negative bus reference is employed, utilizing capacitors to block DC current and reduce common mode noise, allowing for effective ground fault detection and identification in power conversion systems, including those with high resistance grounding configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistive dividers are used for sensing in power conversion systems, then ground fault detection is enabled, but leakage current increases and isolation requirements are not met
Solution Approach 1:
The patent introduces an intermediary circuit configuration using capacitors coupled in series with resistors between the sensing circuit and ground. This intermediary arrangement blocks DC leakage current while allowing AC ground fault signals to pass through for detection, thus resolving the contradiction between enabling ground fault detection and reducing leakage current.
Solution Approach 2:
The patent changes the electrical parameters of the sensing circuit by using capacitive coupling instead of direct resistive connection to ground. This parameter change transforms the circuit from one that allows DC leakage to one that blocks DC while passing AC fault signals, thereby reducing leakage current while maintaining detection capability.
2Ease of operation
If chassis-referenced sensing circuits are used, then ground fault detection is simplified, but leakage current increases significantly
Solution Approach 1:
The patent replaces direct chassis-referenced sensing with an intermediary capacitive coupling arrangement. The capacitors act as mediators that block DC leakage current paths to chassis ground while still allowing AC ground fault voltage signals to be sensed, thus reducing leakage current while maintaining ease of implementation.
3Reliability
If conventional sensing circuits are used in marine applications, then ground fault detection is achieved, but common mode noise reduces detection reliability
Solution Approach 1:
The patent uses capacitive coupling as an intermediary that differentially passes ground fault signals while blocking common mode noise. The capacitors in series with resistors create a high-impedance path for common mode noise while maintaining low-impedance coupling for differential ground fault signals, thereby improving detection reliability in noisy marine environments.
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 provides reliable ground fault detection with low leakage current and improved common mode noise immunity, enabling compliance with marine standards and reducing system downtime in power conversion systems.
Implementation Method 1
A low leakage sensing circuit with a negative bus reference is employed, utilizing capacitors to block DC current
Implementation Method 2
the processor configured to detect a ground fault in the system according to signals from the capacitive coupled sensing circuit
Data Source
AI summary
A power conversion system includes a sensing circuit to sense a system voltage of a DC bus circuit with a first DC bus terminal with a first voltage positive relative to a second voltage of a second DC bus terminal. The sensing circuit includes a first capacitor having a first terminal coupled to the second DC bus terminal, and a second terminal; a second capacitor having a first terminal coupled to the second terminal of the first capacitor, and a second terminal coupled to a reference node; and a resistive divider circuit coupled across the first capacitor and having an output terminal that delivers a voltage signal corresponding to a voltage across the first capacitor.