Excitation H-Bridge Switch Diagnosis by Negative Current Testing
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Solution Overview
Problem
Existing methods struggle to reliably detect a single permanently conductive, defective semiconductor switch in a semi-controlled H-bridge circuit, which is crucial for setting an excitation current for a separately excited synchronous machine.
Innovation Solution
A method and device that utilize a current measuring device to detect a negative current during a freewheeling phase in the H-bridge circuit. By changing the control signal pattern to create a test switching state where one of the semiconductor switches is open, the method evaluates the test current to determine if it is negative, indicating a permanently conductive defective switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single permanently conductive defective semiconductor switch is present in the H-bridge circuit, then the excitation current cannot be properly controlled, but existing detection methods cannot reliably detect this defect
Solution Approach 1:
The invention applies preliminary action by performing a detection operation before normal operation continues. A test switching state is created temporarily to check for defective switches. The method evaluates a test current during a test period where both semiconductor switches should be open, and compares it to a nominal current during normal operation. This preliminary detection prevents undetected defects from causing harmful effects during subsequent normal operation.
Solution Approach 2:
The invention uses feedback by continuously monitoring the total current flowing through the H-bridge circuit and comparing it against expected values. During normal operation, the control signals are evaluated to determine if both switches are open simultaneously. If the measured current deviates from the expected negative current value during this test period, it indicates a defective switch. This feedback mechanism enables reliable detection of single permanently conductive defective switches.
2Loss of energy
If the semiconductor switches are controlled with 50% duty cycle to distribute power loss evenly, then power loss is optimized, but detection of defective switches becomes more difficult
Solution Approach 1:
The invention applies dynamics by temporarily changing the control signal pattern from the normal 50% duty cycle operation to a test switching state. During the test period, both semiconductor switches are opened simultaneously, creating a distinct current signature. This dynamic change in operating state allows for defect detection without permanently altering the optimal power loss distribution achieved during normal operation.
Solution Approach 2:
The invention uses periodic action by implementing regular detection periods interspersed with normal operation periods. The control signals are modified periodically to create test switching states where both switches are open. During these periodic test intervals, the total current is measured and evaluated. This periodic detection approach maintains optimal power loss distribution during normal operation while enabling systematic defect detection at regular intervals.
Data Source
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AI summary
The invention relates to a method for detecting a single permanently conductive defective semiconductor switch (210, 340) of a semi-controlled H-bridge circuit (100) for setting an excitation current of a separately excited synchronous machine, wherein a total current measuring device (180) is connected to the H-bridge circuit (100), which measures the total current IDC flowing through the H-bridge circuit (100); wherein the half-controlled H-bridge circuit (100) is coupled to a control device (1200) which generates two pulse-width modulated control signals (611, 621) of equal frequency and phase-shifted by half a period for controlling the semiconductor switches (210, 340), the method comprising the steps of: a) changing the control signal pattern so that for at least a time-limited test period, a test switching state is created in which one of the semiconductor switches T1 (210) and another of the semiconductor switches T4 (340) are open at the same time,b) measuring a test current flowing through the semi-controlled H-bridge circuit (100) during the test period; c) evaluating whether the test current measured during the at least one test period is negative; d) generating and outputting an error signal if the evaluation shows that the test current measured during the at least one test period is not negative. The invention further relates to a control device and a computer program product that implement the described method.