Sensorless Filter Capacitor Current Measurement Using State Observer
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Solution Overview
Problem
Current methods for measuring filter capacitor current in DC-AC converters face challenges due to ripples, requiring additional hardware and leading to signal distortion and high costs, while indirect detection methods necessitate wide bandwidth detection devices and suffer from delay issues.
Innovation Solution
A sensorless measurement method using a state observer that predicts filter capacitor current by calculating state variable values based on filter-capacitor-voltage and dc-link voltage, eliminating the need for additional hardware and reducing costs by providing average current values without ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct detection with hardware detection circuit is used to measure filter capacitor current, then measurement can be obtained, but additional filter circuit is required which brings signal distortion and delay problems
Solution Approach 1:
The patent replaces the mechanical/electrical hardware detection circuit with a digital signal processing approach using a state observer algorithm. The state observer mathematically reconstructs the filter capacitor current from measured voltage signals, eliminating the need for physical current sensors and filter circuits while maintaining measurement accuracy.
Solution Approach 2:
The patent introduces an intermediary mathematical model (state observer) that indirectly calculates the filter capacitor current from easily measurable voltage signals. This intermediary approach avoids direct current measurement and the associated hardware complexity while providing accurate current information for control purposes.
2Measurement precision
If indirect detection by detecting filter inductor current and load current is used, then filter capacitor current can be calculated as difference value, but at least two detection devices having wide bandwidth are required which increases costs and delay problems
Solution Approach 1:
The patent makes the state observer algorithm serve multiple functions: it simultaneously estimates the filter capacitor current, provides state variables for control, and eliminates the need for separate current sensors. This multi-functional approach reduces the total number of detection devices required while maintaining measurement accuracy.
Solution Approach 2:
The system uses its existing voltage measurement infrastructure to self-generate the filter capacitor current information through the state observer algorithm. No additional detection devices are needed because the system extracts current information from the voltage measurements it already performs for other control purposes.
3Productivity
If filter capacitor current is controlled, then system performance is improved and cheaper detection devices can be utilized, but filter capacitor current has ripples which affects measurement accuracy
Solution Approach 1:
The state observer algorithm extracts the average component of the filter capacitor current by mathematically separating it from the ripple component. The observer model recognizes the known ripple characteristics and subtracts them, leaving only the average current information needed for control while eliminating measurement accuracy issues caused by ripples.
Data Source
AI summary
A sensorless measurement device for filter capacitor current by using a state observer is provided. The sensorless measurement device comprises a chip, wherein the chip comprises the state observer. The state observer is configured to retrieve a filter-capacitor-voltage actual value and a direct current link (dc-link) voltage of a present sampling time. According to the filter-capacitor-voltage actual value and the dc-link voltage, the state observer is configured to output a filter-capacitor-voltage state variable value, a filter-capacitor-current state variable value, and a disturbance-voltage state variable value of a next sampling time. The filter-capacitor-current state variable value is an average current value without ripples.