Overcurrent Detection Using Frequency Analysis in Inverter Control
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Solution Overview
Problem
Existing electrical drive control systems for hybrid and electric vehicles face challenges in accurately detecting overcurrents caused by short-circuit abnormalities, particularly when oscillating currents due to LCR resonance occur, as these currents cannot be reliably detected by existing methods that rely solely on current amplitude threshold comparisons.
Innovation Solution
An overcurrent fault detection device that includes phase current detectors, a rotational position detector, a control circuit, and decision-making circuits capable of frequency detection, using comparators with hysteresis and sample holds to identify overcurrents based on both amplitude and frequency thresholds, thereby distinguishing between normal and fault-induced currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current amplitude threshold comparison methods are used for overcurrent detection, then the detection system remains simple, but it cannot accurately detect overcurrents caused by high-frequency LCR resonance oscillations
Solution Approach 1:
The patent applies dynamics by making the detection threshold dynamic rather than fixed. The threshold is adjusted based on the fundamental wave component of the current, allowing the detection system to adapt to varying operating conditions. This enables accurate detection of resonance oscillations while maintaining system simplicity, as the threshold automatically tracks the fundamental current waveform without requiring complex fixed multiple thresholds.
Solution Approach 2:
The patent uses feedback by continuously monitoring the fundamental wave component of the current and using it to dynamically adjust the detection threshold. The control circuit extracts the fundamental wave component from the total current signal and feeds this information back to the threshold adjustment mechanism, creating a closed-loop system that maintains high detection accuracy across different operating conditions.
2Measurement precision
If high-frequency resonance oscillations occur in fault modes, then overcurrent amplitude exceeds normal levels, but conventional sampling methods at 10 kHz cannot accurately detect these oscillations
Solution Approach 1:
The patent introduces an intermediary approach by using the fundamental wave component as a mediator between the high-frequency resonance oscillations and the detection threshold. Instead of directly sampling and analyzing the high-frequency oscillations (which would require very high sampling rates), the system uses the fundamental wave component to dynamically set the threshold, indirectly detecting the presence of resonance oscillations without needing to resolve their high-frequency content directly.
3Reliability
If fixed amplitude threshold values are used for overcurrent detection, then the detection logic remains simple, but it cannot distinguish between normal high current operation and actual fault conditions
Solution Approach 1:
The patent applies dynamics by making the detection threshold dynamic rather than fixed. The threshold is adjusted based on the fundamental wave component of the current, allowing the detection system to adapt to varying operating conditions. This enables accurate detection of resonance oscillations while maintaining system simplicity, as the threshold automatically tracks the fundamental current waveform without requiring complex fixed multiple thresholds.
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 accurate detection of overcurrents in fault modes such as output ground faults, line-to-line short-circuits, and phase-to-phase short-circuits, preventing transistor damage by turning off gate signals when overcurrents are detected, even in cases where oscillating currents exceed the detection range of conventional methods.
Implementation Method 1
an inverter that converts a DC voltage to an AC voltage
Implementation Method 2
an overcurrent in the inverter output may be caused by LCR resonance assuming a frequency in a range of several kHz through a frequency exceeding 100 kHz
Data Source
AI summary
According to the present invention, an overcurrent fault detection device includes: an inverter converting DC current to three-phase AC currents for driving a motor; a DC voltage detector; phase current detectors; a rotational position detector that detects a rotational angle of the motor; a control circuit that controls a gate drive circuit, which controls the inverter at every predetermined cycle, based upon the phase current values, a motor rotational angle detection value, and a speed command or a torque command from a higher-order control device; and a first decision-making circuit that detects an overcurrent based upon the phase current values at every predetermined cycle, wherein: the first decision-making circuit determines whether or not the phase current values exceed a predetermined amplitude threshold value by frequency detection for any of the phase current values exceeding the predetermined amplitude threshold value, and determines that an overcurrent has occurred upon detecting the frequency.