AC/DC Converter Rectifier Fault Detection via AC Current Ripple
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Solution Overview
Problem
Existing methods fail to effectively detect and differentiate between non-conductive and short-circuited rectifiers in AC/DC converters, which can lead to unbalanced voltages and potential damage to rotor systems in synchronous rotating electrical machines.
Innovation Solution
A method that measures instantaneous AC currents, estimates the instantaneous DC current, calculates a ripple value, and determines rectifier status based on maximum and minimum AC phase currents to identify non-conductive or short-circuited faults, initiating an alarm and allowing for corrective action.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing detection methods (RMS phase current ratio or DC current ripple measurement) are used, then detection capability is limited, but device complexity and measurement requirements increase
Solution Approach 1:
The patent extracts the detection function from complex measurement systems by using only AC current measurements that are already available in the system. The method takes out the essential detection capability from the complicated setup of DC current measurement and ripple analysis, achieving fault detection through simplified AC side measurements combined with mathematical modeling of the rectifier circuit behavior.
Solution Approach 2:
The patent makes the AC current measurement system multi-functional by using it not only for power control but also for fault detection. The same AC current sensors and measurement channels used for normal operation are leveraged to detect rectifier failures, eliminating the need for separate detection hardware and achieving universal use of existing measurement infrastructure.
2Reliability
If DC current and ripple measurement is implemented, then non-conductive diode detection is possible, but measurement precision and reliability are insufficient for distinguishing fault types
Solution Approach 1:
The patent introduces an intermediary approach by using AC current measurements as a mediator to infer DC side fault conditions. Instead of directly measuring DC current ripple with insufficient precision, the method uses precisely measurable AC currents combined with circuit modeling to indirectly detect and differentiate fault types, achieving higher reliability through the intermediary measurement path.
Solution Approach 2:
The patent changes the measurement parameter from DC current ripple (which has insufficient precision) to AC current characteristics (which can be measured with high precision). By analyzing changes in AC current parameters during different conduction intervals and comparing them with theoretical models, the system achieves reliable fault type differentiation without being limited by DC measurement precision.
3Reliability
If comprehensive fault detection is implemented, then system safety is improved, but ease of operation and response time are reduced
Solution Approach 1:
The patent implements self-service detection where the system automatically monitors itself using its existing measurement capabilities. The control unit performs the detection, analysis, and fault identification without requiring external measurement equipment or complex operational procedures. The system serves its own detection needs by leveraging its inherent AC current measurement functionality, making the process simple and automatic.
Data Source
Figure 1a~1b
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Figure 3~3a
AI summary
The present invention relates to a device (1) for detecting a failed rectifier in three-phase AC/DC converter having its AC side connected to a three-phase AC source (90) and its DC side connected to a DC load (50), the AC/DC converter including a rectifier circuit (30) comprising at least three legs (31, 31', 31"), each of the legs (31, 31', 31") connected to a corresponding AC phase (40) and including at least one rectifier (32, 34, 32', 34', 32", 34"), the device (1) including a measuring unit (20) for measuring and sampling AC current for each of the phases and a calculating unit (10) configured to estimate an instantaneous DC current based on the measured instantaneous AC currents during one period of the power supply frequency. The calculating unit (10) is further configured to calculate a ripple value of the estimated instantaneous DC current, determine if the calculated ripple value exceeds a pre-defined threshold value, initiate an alarm accordingly, calculate a rectifier status value based on a maximum instantaneous AC phase current and a minimum instantaneous AC phase current during the same one period, and determine, for each of the legs, if the rectifier in the leg has a non-conducting fault based on the calculated rectifier status value.