Digital Phase-Locked Loop for Simultaneous Power Measurement
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Solution Overview
Problem
Current methods for measuring active and reactive powers in electrical power systems, particularly at fundamental and harmonic frequencies, are inefficient due to longer calculation times and inability to compute these powers simultaneously in near real-time, especially when dealing with non-linear loads that introduce harmonic content.
Innovation Solution
The use of a digital phase-locked loop (DPLL) to generate orthogonal reference signals, allowing for simultaneous measurement of active and reactive powers at fundamental and harmonic frequencies by correlating input voltage and current signals, with low-pass filters to reject non-DC components and automatic gain correction to minimize phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Digital Fourier Transform (DFT) and band-pass filters are used to compute active and reactive power, then measurement can be performed, but calculation time increases and near real-time computation is not achieved
Solution Approach 1:
The patent replaces traditional digital signal processing methods (DFT and band-pass filters) with a phase-locked loop (PLL) based measurement system. The PLL circuit provides a more efficient mechanism for extracting active and reactive power components by locking onto the fundamental frequency and harmonics, thereby reducing calculation time while maintaining measurement accuracy.
Solution Approach 2:
The patent changes the measurement approach by using PLL to track phase and frequency parameters dynamically. By adjusting the PLL to lock onto different frequency components (fundamental and harmonics), the system can compute active and reactive powers at multiple frequencies simultaneously without the computational burden of DFT, achieving near real-time performance.
2Measurement precision
If traditional measurement methods are used, then active and reactive power can be measured, but simultaneous measurement at multiple frequencies is not achieved
Solution Approach 1:
The patent implements a universal measurement system based on PLL that can simultaneously measure active and reactive powers at multiple frequencies (fundamental and harmonic frequencies). The PLL-based architecture provides multi-functionality by handling different frequency components through a unified measurement framework, improving both accuracy and measurement speed compared to traditional single-frequency methods.
3Device complexity
If phase offset between voltage and current is not corrected, then measurement is simpler, but measurement accuracy deteriorates due to phase errors
Solution Approach 1:
The patent employs feedback mechanisms within the PLL circuit to automatically detect and correct phase offsets between voltage and current signals. The PLL continuously adjusts its phase to lock onto the reference signal, providing real-time phase error correction. This feedback-based approach maintains high measurement accuracy without significantly increasing system complexity, as the correction is performed automatically by the PLL architecture.
Data Source
AI summary
A method for measuring active power of alternating current (AC) using a digital phase-locked loop (DPLL) includes the steps of (1) generating via the DPLL a pair of substantially mutually orthogonal sinusoid signals in response to an input voltage data signal, (2) mixing a first sinusoid signal of the pair with a current data signal of the alternating current via a first low-pass filter, (3) mixing the first sinusoid signal of the pair with a voltage signal of the alternating current via a second low-pass filter, and (4) computing an active power of the alternating current based on an output from the first low-pass filter and an output from the second low-pass filter.