DC Link Voltage Spectrum Analysis for Three-Phase Imbalance Detection
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Solution Overview
Problem
Existing methods for assessing three-phase AC power supply imbalance in power conversion devices only detect input phase loss and fail to correctly identify voltage unbalanced states that do not lead to phase loss, potentially causing device damage.
Innovation Solution
A method and device that use a forward converter, smoothing capacitor, detection unit, and control unit to assess voltage imbalance by comparing the magnitudes of frequency components at four times and six times the power supply frequency in the power conversion device, allowing for the identification of unbalanced states beyond phase loss conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only input phase loss detection is implemented, then device complexity is reduced, but measurement precision of voltage imbalance is insufficient
Solution Approach 1:
The patent changes the detection parameter from simple phase presence/absence to frequency component analysis. By performing FFT on the DC voltage and comparing the magnitudes of 4f and 6f components, the system achieves precise measurement of voltage imbalance while using existing hardware components, thus resolving the contradiction between device complexity and measurement precision.
2Measurement precision
If frequency component analysis is performed to detect voltage imbalance, then measurement precision is improved, but loss of time for processing increases
Solution Approach 1:
The patent extracts only the specific frequency components (4f and 6f) that are most indicative of voltage imbalance from the full频谱 analysis. By focusing on these two critical frequency components rather than analyzing the entire frequency spectrum, the system achieves accurate imbalance detection while minimizing processing time and computational resources.
3Reliability
If comprehensive voltage imbalance assessment is implemented, then reliability of device protection is improved, but device complexity increases
Solution Approach 1:
The patent utilizes the existing DC voltage from the rectifier circuit and smoothing capacitor as the detection source, rather than adding separate voltage sensors for each phase. The control unit performs FFT analysis on this readily available DC voltage signal, allowing the system to achieve comprehensive voltage imbalance assessment while avoiding the complexity of additional sensing hardware and signal conditioning circuits.
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
Enables the accurate assessment of three-phase AC power supply voltage imbalance, preventing device damage by detecting unbalanced states that may not result in phase loss, thereby enhancing electrical safety and monitoring of power quality.
Implementation Method 1
a forward converter 4 (converter, also referred to as a rectifier circuit) that converts AC power of the three-phase AC power supply 2 into DC power
Implementation Method 2
a smoothing capacitor 5 that smooths a DC voltage after rectification of the forward converter 4
Implementation Method 3
A voltage detection circuit 7 that detects a DC voltage between both ends of the smoothing capacitor 5 is connected to the control circuit 8
Implementation Method 4
The arithmetic operation device 10 performs a fast Fourier transform (FFT) on the N pieces of time-series data
Implementation Method 5
the arithmetic operation device 10 compares the magnitudes of a component being four times the power supply frequency and a component being six times the power supply frequency in the amplitude spectrum
Data Source
Figure 1
Figure 2A(a)~2A(b)
Figure 2B(a)~2B(b)
AI summary
This voltage imbalance assessment method is for a power conversion device comprising a forward converter for rectifying the voltage of a three-phase AC power supply, a smoothing capacitor for smoothing the rectified voltage, a detection unit for detecting the smoothed voltage, and a control unit. The control unit: uses the detected voltage to generate data indicating frequency components; compares, in the data indicating frequency components, the magnitude of the component that is four times the power supply frequency with the magnitude of the component that is six times the power supply frequency; and assesses the voltage imbalance of the three-phase AC power supply on the basis of the comparison.