Active Filter Phase Correction for Variable Harmonic Impedance
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Solution Overview
Problem
Existing active filter apparatuses struggle to effectively suppress harmonics in power systems due to varying impedance characteristics, which can change from inductive to capacitive, leading to inadequate harmonic suppression.
Innovation Solution
A control device for an active filter that includes a harmonic voltage detector, phase corrector, command value generator, and output controller, capable of adjusting phase correction based on impedance characteristics to generate appropriate compensation commands, thereby reducing harmonics regardless of impedance state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a converter circuit with reactive elements is used to convert fundamental frequency components, then power conversion efficiency is improved, but the device cannot process higher frequency components effectively
Solution Approach 1:
The patent divides the frequency processing task into multiple independent parallel circuits, each dedicated to a specific frequency component (fundamental frequency and harmonic frequencies). This segmentation allows each circuit to be optimized for its specific frequency while collectively covering the full spectrum of distortion components.
Solution Approach 2:
The patent creates a multi-functional system where multiple converter circuits operate simultaneously to handle different frequency components. The control device universally processes both fundamental frequency and harmonic frequency components through coordinated control of multiple circuits, achieving broad frequency coverage.
2Adaptability or versatility
If multiple converter circuits are operated in parallel to process multiple frequency components, then frequency processing capability is improved, but control complexity increases
Solution Approach 1:
The patent employs feedback control where the control device continuously monitors the output of each converter circuit and adjusts control signals accordingly. This feedback mechanism coordinates the parallel circuits, maintaining synchronization and ensuring that each circuit contributes effectively to the overall waveform reconstruction.
Solution Approach 2:
The control device performs preliminary analysis of the distortion waveform to identify fundamental and harmonic frequency components before distributing control signals to the respective converter circuits. This preliminary action simplifies the real-time control burden by pre-processing the frequency spectrum information.
Data Source
Figure 1~2(b)
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AI summary
A control device (100) for an active filter (80) connected in parallel with a load (4b) at an installation point (4a) with respect to an AC power supply (2) provided in a power system includes a harmonic voltage detector (7) to detect an m-order harmonic voltage (m is an integer not less than two) included in a voltage of the installation point (4a), a phase corrector (9) to correct a phase of the detected m-order harmonic voltage in accordance with whether an m-order harmonic impedance when an AC power supply (2) side is seen from the installation point (4a) is capacitive or inductive, a command value generator (10) to generate a first compensation command value for compensating for the m-order harmonic voltage included in the voltage of the installation point (4a) based on the m-order harmonic voltage after the correction, and an output controller (18) to control an output of the active filter (80) based on a first compensation command value.