Adaptive Online Filter for DC Offset Elimination in Power Converters
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Solution Overview
Problem
Existing power conversion systems face challenges in synchronizing with grid power due to low frequency or DC offsets and higher order harmonics in phase voltage sensors, which corrupt the phase signal output from phase lock loops, and current solutions either require additional hardware or suffer from bandwidth limitations.
Innovation Solution
An adaptive online filtering technique using an adaptive tracking filter and a low pass filter to remove frequency components outside a defined passband, generating a modified signal with the DC offset component substantially removed, thereby improving phase angle detection and synchronization without adding hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tracking filters are used in the feedback loop of a PLL to eliminate error signal disturbances, then measurement precision is improved, but device complexity increases due to additional hardware requirements
Solution Approach 1:
The patent extracts and removes the DC offset component from the phase voltage sensor signal using a dedicated offset removal circuit before the signal enters the PLL. This separates the offset elimination function from the main PLL structure, improving phase signal accuracy without requiring complex tracking filters within the PLL feedback loop.
Solution Approach 2:
The patent applies preliminary action by removing the DC offset component from the sensor signal before it is processed by the PLL. The offset removal circuit processes the signal in advance, preventing the offset from corrupting the phase signal generation, thereby improving measurement precision without adding complexity to the PLL itself.
2Measurement precision
If harmonic tracking filters are implemented in conjunction with a tracking filter at the fundamental frequency, then measurement precision is improved, but bandwidth limitations occur due to filter bandwidth overlap
Solution Approach 1:
The patent segments the signal processing functions into distinct stages: DC offset removal is performed in a separate circuit before the PLL, while the PLL handles fundamental frequency tracking. This segmentation prevents bandwidth overlap between filters and maintains PLL bandwidth, as the offset removal does not compete with the fundamental frequency tracking for bandwidth resources.
Solution Approach 2:
The patent introduces an intermediary offset removal circuit between the sensor and the PLL. This intermediary component handles the DC offset elimination separately, allowing the PLL to focus on fundamental frequency tracking without interference from offset correction, thereby maintaining optimal bandwidth and avoiding filter overlap issues.
3Measurement precision
If low pass filter nulling is used to remove DC offset, then measurement precision is improved, but device complexity increases due to additional hardware
Solution Approach 1:
The patent merges the DC offset removal function with the existing signal processing path by implementing the offset removal circuit in a manner that integrates with the phase voltage sensing system. This combination approach eliminates the need for completely separate additional hardware, reducing overall device complexity while maintaining measurement precision through effective DC offset removal.
Data Source
AI summary
A phase angle detector with a PLL, a power converter, and a method for reducing offsets in an input signal, in which an adaptive offset processor selectively removes a DC offset component from the input signal to generate a modified signal including a fundamental frequency component and higher order harmonics of the input signal with the DC offset component removed, and the PLL provides a phase angle signal at least partially according to the modified signal.