Inverter AC Capacitor Failure Detection Using dq Current Conversion
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Solution Overview
Problem
In power conversion devices with parallel-connected alternating-current capacitors, open failures in some capacitors distort the voltage waveform, and conventional methods fail to detect these failures during operation, leading to potential spread of failure to normal capacitors and outflow of harmonics.
Innovation Solution
A control device is introduced that includes a conversion value calculation unit to acquire current values from alternating-current capacitors and perform dq conversion, and a failure detection unit that compares the conversion values with predetermined determination values to detect capacitor failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple alternating-current capacitors are connected in parallel to increase capacitance, then the capacitance of the capacitor circuit is improved, but the reliability of the system deteriorates due to undetected open failures that can spread to normal capacitors
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the q-axis current of each capacitor and comparing it with a predetermined threshold value. When the q-axis current deviates from the expected range, the system generates a failure signal to alert operators. This feedback loop enables real-time detection of open failures in parallel-connected capacitors, preventing failure propagation while maintaining the high capacitance achieved through parallel connection.
2Device complexity
If conventional monitoring methods are used without dq conversion, then the device complexity is reduced, but the measurement precision of capacitor failure detection deteriorates
Solution Approach 1:
The patent transforms the monitoring approach by changing the parameter domain from time-domain current measurement to frequency-domain analysis through dq conversion. By converting the three-phase current signals into rotating reference frame components (d-axis and q-axis currents), the system can precisely detect capacitor failures based on q-axis current magnitude. This parameter transformation enables accurate failure detection while maintaining relatively simple device complexity, as the conversion can be implemented through standard control algorithms.
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 enables early detection of alternating-current capacitor failures, preventing the spread of failure to normal capacitors and reducing the outflow of harmonics to the system side.
Implementation Method 1
the conversion value calculation unit by performing dq conversion of the current value of each current of each of phases flowing in a plurality of the alternating-current capacitors that are connected in parallel
Data Source
AI summary
A control device is a control device of a power conversion device, and includes a conversion value calculation unit that acquires a current value of a current flowing in an alternating-current capacitor connected to a capacitor circuit in an output circuit on an alternating-current side of an inverter circuit and performs conversion of the current value to obtain a predetermined conversion value, and a failure detection unit that compares the conversion value obtained by the conversion value calculation unit and a predetermined determination value to be used in failure detection to detect a failure of the alternating-current capacitor.