Three-Phase Inverter Ground Fault Detection Using Zero-Phase Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The insulation deterioration of auxiliary load circuits in railroad vehicles is difficult to detect accurately due to ground fault currents being smaller than overcurrents, leading to increased false positives in overcurrent protection.
Innovation Solution
A power conversion apparatus equipped with a three-phase inverter, a filter circuit comprising a three-phase reactor and capacitor circuit, a voltage detector, and a control device that calculates zero-phase voltage, separates it into AC and DC signals, and determines ground faults based on the AC signal's effective value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the determination value for overcurrent protection is lowered to detect ground fault current, then the detection sensitivity for insulation deterioration is improved, but the number of false positives in overcurrent protection increases
Solution Approach 1:
The invention segments the detection function into two independent systems: overcurrent protection detection and ground fault detection. Each system has its own determination value threshold. The ground fault detection unit calculates ground fault current separately from the overcurrent detector, allowing independent optimization of detection sensitivity without affecting overcurrent protection reliability.
Solution Approach 2:
The invention introduces a ground fault detection unit as an intermediary component that calculates ground fault current by subtracting the sum of three-phase currents from the neutral line current. This intermediary calculation method enables separate detection of ground fault currents without interfering with the overcurrent protection system, resolving the contradiction between detection sensitivity and false positive rate.
2Reliability
If the determination value for overcurrent protection is maintained at a high level to reduce false positives, then the reliability of overcurrent protection is improved, but the ability to detect ground fault current deteriorates
Solution Approach 1:
The detection system is segmented into independent overcurrent protection and ground fault detection functions. The ground fault detection unit operates with its own determination value that is specifically optimized for detecting small ground fault currents, while the overcurrent protection maintains its higher threshold for reliability. This segmentation allows each function to operate at its optimal detection level without compromising the other.
3Device complexity
If the overcurrent detector is used to detect ground fault current, then the device complexity is reduced, but the measurement precision for ground fault detection deteriorates
Solution Approach 1:
The ground fault detection unit acts as an intermediary that processes current measurements to specifically extract ground fault current components. It calculates the ground fault current by subtracting the sum of three-phase currents from the neutral line current, providing precise ground fault detection without requiring complete redesign of the detection system. This intermediary approach adds minimal complexity while significantly improving measurement precision for ground faults.
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
This solution enables early and accurate detection of insulation deterioration in auxiliary load circuits, reducing the number of false positives and improving the reliability of protection systems.
Implementation Method 1
a three-phase inverter (10) to convert input power to alternating-current power and supply the alternating-current power obtained by conversion to a load
Implementation Method 2
a voltage detector (11) to detect three-phase voltages that are voltages at respective connection points between the three-phase reactor circuit and the three-phase capacitor circuit
Data Source
AI summary
A power conversion apparatus includes: a three-phase inverter that supplies alternating-current power obtained by conversion to a load via a filter circuit including a three-phase reactor circuit and a three-phase capacitor circuit; a voltage detector that detects three-phase voltages that are voltages at respective connection points between the three-phase reactor circuit and the three-phase capacitor circuit; and a control device that controls operation of the three-phase inverter on the basis of the three-phase voltages detected by the voltage detector. The control device includes a calculation unit that calculates a zero-phase voltage obtained by adding together the three-phase voltages, a separation unit that separates an instantaneous value of the zero-phase voltage into an alternating-current signal and a direct-current signal, and a first determination unit that determines whether a ground fault occurs on the basis of an effective value of the alternating-current signal.