PFC Converter Harmonic Removal With Adaptive Current Sensing

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Solution Overview

Problem

Existing power factor correction (PFC) solutions face challenges in efficiently correcting power factor at low power demands due to high-speed current sense loops, which are power inefficient and complex, and struggle with maintaining a constant frequency, leading to difficulties in filtering switching noise and electromagnetic interference (EMI).

Innovation Solution

The proposed electrical circuit for PFC uses a converter with switches and inductors, incorporating adaptive current sensing circuitry and operational circuitry to generate error signals. These error signals are used to control the switches, minimizing overtones and phase errors, thereby improving power factor without the need for high-speed current sense loops or multiplier circuits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high-speed current sense loops are used for power factor correction, then power factor correction capability is improved, but power efficiency deteriorates and circuit complexity increases

Engineering Contradiction:

Improvepower factor correction capabilityVSAvoidpower efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent replaces the high-speed current sense loop (analog control system) with a digital signal processing approach. The controller measures the AC input voltage and current, digitally processes these signals to detect harmonic content, and generates control signals to correct the power factor. This substitution of analog high-speed sensing with digital measurement and processing reduces power consumption while maintaining correction capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an intermediary digital processing stage between the current measurement and the control action. Instead of directly using high-speed analog current sense loops, the system uses a controller that measures and digitally processes the current signal to identify harmonics, then generates appropriate correction signals. This intermediary digital processing layer reduces the power efficiency penalty associated with high-speed analog sensing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If high-speed current sense loops are used for power factor correction, then power factor correction capability is improved, but device complexity increases

Engineering Contradiction:

Improvepower factor correction capabilityVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex high-speed analog current sense loop circuitry with a digital controller that performs measurements and signal processing. The digital approach simplifies the hardware by eliminating the need for high-speed analog sensors and associated complex analog circuitry, while maintaining the power factor correction capability through digital algorithms.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The controller performs multiple functions: measuring AC input voltage, measuring AC input current, detecting harmonic content, generating power factor correction control signals, and regulating output voltage. By consolidating these functions into a single digital controller rather than separate dedicated circuits for each function, the overall device complexity is reduced.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If variable frequency operation is used to adapt to changing power demands, then adaptability is improved, but filtering switching noise and EMI becomes more difficult

Engineering Contradiction:

Improveadaptation to power demand changesVSAvoidswitching noise and EMI filtering

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent employs periodic switching at a fixed frequency to generate the output voltage. By maintaining a constant switching frequency rather than varying it with power demand, the system creates predictable periodic action that allows for effective filtering of switching noise and EMI using fixed-frequency filters, while still adapting to power demand changes through pulse width modulation of the fixed-frequency switches.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS12294295B2Systems and methods of unwanted harmonic content removal for power conversion

Publication Date: 2025.05.06 WRATHALL ROBERT S

AI summary

Provided are electrical circuits and methods for power factor correction. An example method includes receiving, by converter, an input voltage at a fundamental frequency and generating an output voltage; generating, based on the output voltage, a first measurement signal; subtracting a first reference signal from the first measurement signal to obtain a first error signal; generating an adaptive current sense signal, generating a reference voltage based on the input voltage, subtracting the reference voltage from the current sense signal thus generating a second measurement signal to control the current measurement; subtracting the second measurement signal from the input voltage to obtain a difference signal, wherein the difference signal is largely minimized by removing overtones of the fundamental frequency; generating, based on the difference signal, a second error signal; using a sum of the second error signal as a first order correction to the first error signal to regulate the converter.