SMPS Input Power Measurement Using Zero-Crossing Frequency Detection
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Solution Overview
Problem
Existing AC-DC switched mode power supplies (SMPS) face challenges in accurately determining input current and power due to variations in power line frequency and reactive currents through capacitive filters, leading to inaccuracies in power measurements.
Innovation Solution
A method for determining AC input current in SMPS by identifying zero crossings of the analog signal representing the difference between AC line and neutral voltages, calculating power line frequency, and compensating for reactive currents using a control circuit with differential amplifiers and digital controllers to accurately determine input current without the need for conventional power-metering devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional power-metering chips are used to measure input current and voltage, then power measurement function is provided, but measurement precision deteriorates due to power line frequency variations and reactive currents through capacitive filters
Solution Approach 1:
The patent replaces conventional power-metering chips with a measurement approach based on zero-crossing detection and frequency calculation using differential amplifiers and digital controllers. This substitution eliminates the reliance on fixed-frequency assumptions and reactive current compensation mechanisms inherent in conventional chips, achieving accurate input current measurement despite power line frequency variations and capacitive filter effects
Solution Approach 2:
The patent dynamically adapts to power line frequency changes by calculating the actual frequency from zero-crossing intervals and adjusting measurements accordingly. Instead of assuming a fixed frequency, the system continuously updates its measurement parameters based on the actual operating conditions, thereby maintaining measurement precision across varying frequency conditions
2Measurement precision
If power-metering chips are used, then power measurement capability is achieved, but device complexity is reduced while measurement precision deteriorates
Solution Approach 1:
The patent replaces integrated power-metering chips with a distributed measurement system using basic analog components (differential amplifiers) and digital processing. This approach achieves superior measurement precision by explicitly calculating frequency and compensating for reactive currents, while the complexity is managed through algorithmic solutions rather than complex hardware integration
Solution Approach 2:
The measurement function is segmented into distinct operational steps: zero-crossing detection, frequency calculation, reactive current determination, and input current computation. This segmentation allows each function to be optimized independently and implemented using simple, well-understood components and algorithms, achieving high precision without requiring a complex monolithic device
3Ease of operation
If external power-metering devices are used, then measurement function is provided, but ease of operation deteriorates due to additional components
Solution Approach 1:
The patent merges the power measurement function into the existing control circuit of the SMPS by using the same differential amplifiers and digital controllers already present for other control functions. This integration eliminates the need for separate external power-metering devices, simplifying the overall system while maintaining measurement capability
Solution Approach 2:
The control circuit components (differential amplifiers and digital controllers) are designed to perform multiple functions: both the standard control functions and the power measurement functions. This multi-functionality eliminates the need for dedicated external measurement devices, reducing component count and simplifying system operation while achieving accurate power measurements
Data Source
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AI summary
A switched mode power supply (SMPS) includes a filter, a power factor correction (PFC) circuit, and a control circuit configured to determine various electrical parameters of the SMPS. In some embodiments, the control circuit is configured to determine a power line frequency and an AC input voltage based on an AC line voltage and an AC neural voltage. In other embodiments, the control circuit is configured to determine an AC input current based on a reactive current flowing through the filter and a PFC AC current. In further embodiments, the control circuit is configured to report a value of an electrical parameter if value is determined to be accurate. Other example switch mode power supplies, control circuits and methods are also disclosed.