Leakage Current Calculation Device Frequency Synchronization
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Solution Overview
Problem
Existing leakage current calculation devices inaccurately calculate insulation resistance-to-ground leakage current when the system frequency of a commercial power system and the operating frequency of an inverter device are the same, due to the inability to distinguish between leakage current components synchronized with these frequencies.
Innovation Solution
A device and method that include a voltage measuring part, a voltage-to-ground calculating part, a leakage current measuring part, a frequency component extracting part, a phase difference determining part, and a leakage current calculating part, which calculate the insulation resistance-to-ground leakage current by extracting frequency components and determining phase differences at multiple time points to identify the center of a circle described by these components, allowing accurate calculation even when frequencies are equal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the system frequency of the commercial power system and the operating frequency of the inverter device are set to the same value, then the device can operate efficiently with synchronized frequencies, but an error occurs in the calculated leakage current due to inability to distinguish between leakage current components synchronized with these frequencies
Solution Approach 1:
The patent segments the leakage current measurement into multiple frequency components using Fourier transform. By dividing the leakage current signal into different frequency components (system frequency and operating frequency), the device can separately analyze and calculate the insulation resistance-to-ground leakage current even when both frequencies are identical, thus resolving the measurement accuracy issue while maintaining operational efficiency
Solution Approach 2:
The patent introduces phase difference as an intermediary parameter to distinguish between leakage current components. By measuring the phase difference between voltage-to-ground and leakage current component at multiple time points and using circle description method, the device can identify the specific leakage current component corresponding to the system frequency, enabling accurate calculation without requiring frequency differentiation
2Measurement precision
If frequency component extraction and phase difference determination are performed at multiple time points to accurately identify leakage current components, then measurement accuracy improves, but calculation complexity and processing time increase
Solution Approach 1:
The patent employs periodic sampling at multiple time points to capture the phase difference characteristics of leakage current components. By performing measurements at strategically selected time points and using the periodic nature of AC signals, the device can accurately determine the circle center representing the leakage current component while avoiding continuous monitoring, thus balancing measurement accuracy with processing efficiency
Solution Approach 2:
The patent uses circle description method where multiple measured points are used to construct a circle, and the center of this circle represents the desired leakage current component. This geometric approach simplifies the complex calculation by transforming it into a visual and computationally efficient circle-fitting problem, reducing the overall calculation complexity while maintaining high measurement accuracy
Data Source
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Figure 3~4B
AI summary
A resistance leakage current calculating part (17) calculates an insulation resistance-to-ground leakage current corresponding to a system frequency of a commercial power system (2), which flows through an insulation resistance-to-ground of a three-phase motor (5) between the three-phase motor (5) and the ground (E) on the basis of a center of a circle which is described by specific points which are specified by a leakage current component and a phase difference which are extracted and calculated at three or more different time points. Accordingly, when the system frequency of the commercial power system and an operating frequency of an inverter device are the same, it is possible to accurately calculate an insulation resistance-to-ground leakage current corresponding to the system frequency.