Mutual Inductance Current Sensing for Harmonic Clipping Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional current measurement systems using mutual inductance sensors face challenges in accurately measuring high-order harmonics due to the frequency response of these sensors, which can lead to signal clipping and reduced dynamic range, especially when dealing with non-sinusoidal currents in modern power distribution systems.
Innovation Solution
A signal processing arrangement that combines analogue low-pass filtering with digital signal processing to compensate for the frequency and phase responses of the mutual inductance sensor and low-pass filter, allowing for improved dynamic range and accuracy in measuring high harmonic currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mutual inductance sensor is used to measure current over a wide dynamic range, then electrical isolation and linearity are improved, but the frequency response increases at 20 dB/decade causing signal clipping and compromised dynamic range
Solution Approach 1:
The patent applies preliminary action by implementing an anti-aliasing low-pass filter before the ADC to pre-attenuate high-frequency harmonic components. This preliminary filtering prevents signal clipping and preserves the dynamic range for measuring fundamental and lower harmonic currents, resolving the contradiction between the sensor's wide bandwidth capability and the ADC's limited input range.
Solution Approach 2:
The patent applies parameter changes by using digital signal processing to compensate for the low-pass filter's frequency response. Digital filters and processing algorithms adjust the filtered signal to restore accurate magnitude and phase measurements across the measurement bandwidth, overcoming the attenuation introduced by the anti-aliasing filter while maintaining electrical isolation and linearity.
2Measurement precision
If an anti-aliasing low-pass filter is added before the ADC, then signal clipping is reduced and dynamic range is improved, but device complexity increases
Solution Approach 1:
The patent uses digital signal processing as an intermediary to bridge the gap between the filtered analog signal and the required measurement accuracy. Digital filters and processing algorithms compensate for the analog low-pass filter's frequency response, restoring measurement precision without requiring complex analog circuitry, thus managing device complexity while improving dynamic range.
3Measurement precision
If digital filtering is used to compensate for frequency response, then measurement accuracy is improved, but device complexity and processing requirements increase
Solution Approach 1:
The patent replaces complex analog filtering and integration circuits with digital signal processing. By performing frequency and phase compensation in the digital domain after ADC conversion, the system achieves high measurement accuracy without the stability and tolerance issues of analog components, managing complexity through software-based solutions rather than complex hardware.
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 approach enhances the dynamic range of current measurements and maintains accuracy across a wide range of frequencies, including high-order harmonics, by attenuating harmonic components in the analogue domain and compensating for phase and amplitude errors in the digital domain, thus meeting modern standards for power measurement.
Implementation Method 1
Mutual inductance sensors, for example Rogowski coil sensors, have become increasingly popular because they provide electrical isolation, and because of their inherent linearity over a wide dynamic range of currents
Implementation Method 2
A signal processing arrangement combining a low-pass filter with a digital processing chain to compensate for the frequency and phase responses
Data Source
AI summary
Mutual inductance-type current sensing apparatus (1) is described which includes a mutual inductance current sensor (11) having a first transfer function. The apparatus (1) also includes a low-pass filter (12) which receives a signal from the current sensor (11). The low-pass filter (12) has a second transfer function configured to attenuate one or more harmonic components of the signal. The apparatus (1) also includes an analogue-to-digital converter (13) which receives and digitises a filtered signal output from the low-pass filter. The apparatus (1) also includes a controller (8) configured to process a digitised signal from the analogue-to-digital converter (13) using a digital processing chain configured to compensate for the frequency and phase responses of the first transfer function and the second transfer function.