Inverter Power Relay Fault Detection via DC Link Voltage Drop
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Solution Overview
Problem
Existing fault detection methods for power relays in inverters are inadequate, as they may cause damage to the initial charge resistor and internal inverter structure due to inrush currents and lack a reliable, efficient means to determine relay faults.
Innovation Solution
An apparatus using a single voltage sensor to measure voltage drops across the DC link, a current sensor to measure output currents, and a controller to determine faults by comparing voltage drop rates and durations, employing a time constant and resistance calculations to differentiate between normal and faulty relay operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power relay is used to prevent inrush current during initial charging, then the initial charge resistor is protected from damage, but the relay may fail during motor operation causing current to flow through the resistor again and damage it
Solution Approach 1:
The patent replaces mechanical fault detection methods with electrical measurement and calculation. By using voltage sensors to measure voltage drops across the DC link and initial charge resistor, and calculating the difference to detect relay faults, the system eliminates the need for complex mechanical monitoring mechanisms while improving detection reliability.
Solution Approach 2:
The patent introduces voltage sensors as intermediary measurement devices between the power relay and the control system. These sensors measure voltage drops and provide data to the controller, which then determines relay status based on calculated voltage differences, creating an indirect but reliable detection mechanism.
2Measurement precision
If multiple sensors are used to detect power relay faults, then detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the voltage sensor serve multiple functions: measuring the overall DC link voltage and simultaneously detecting power relay faults by calculating voltage drops. This multi-functionality eliminates the need for separate dedicated fault detection sensors, reducing device complexity while maintaining detection accuracy.
Solution Approach 2:
The patent changes the approach from direct current measurement to voltage measurement and calculation. By measuring voltage drops across the DC link and initial charge resistor and calculating the difference, the system achieves accurate fault detection using voltage parameters rather than requiring direct current sensing, thereby reducing sensor requirements.
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
Effectively detects faults in power relays by accurately determining voltage drop rates and durations, preventing damage to the initial charge resistor and inverter components, and providing a reliable, efficient method for fault identification.
Implementation Method 1
a voltage sensor configured to measure a voltage of a DC link
Implementation Method 2
a current sensor configured to measure an output current to an inverter stage
Implementation Method 3
compare the difference between the voltages with a voltage drop determined by the output current and the resistance
Data Source
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AI summary
An apparatus for detecting a fault in a power relay of an inverter is disclosed. The apparatus for detecting a fault in a power relay includes: a voltage sensor configured to measure a voltage of a DC link; a current sensor configured to measure an output current applied to an inverter stage; a storage unit configured to store resistance of an initial charge resistor, a time constant of a capacitor, and a reference voltage measured when voltage drop of the DC link does not occur; and a controller configured to determine, when the voltage drop of the DC link occurs, the presence or absence of a fault in the power relay based on a difference between the reference voltage and a voltage measured after lapse of a period corresponding to the time constant.