Actively Switched PFC Circuit for Sinusoidal Current Control
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Solution Overview
Problem
Power factor correction circuits with filter capacitors fail to accurately follow the sinusoidal mains AC voltage, leading to undesirable harmonic distortion and current peaks due to the capacitor's voltage drop after the rectified AC voltage peak, resulting in inefficient and non-sinusoidal current consumption.
Innovation Solution
An actively switched power factor correction circuit with a control circuit that adjusts the switch-on time based on measured capacitor voltage, aiming to match the sinusoidal profile of the mains AC voltage, inverting every second half-wave, to regulate the capacitor voltage and ensure sinusoidal current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a filter capacitor is used downstream of the rectifier to smooth the rectified AC voltage, then the voltage stability is improved, but the current consumption becomes non-sinusoidal and harmonic distortion increases
Solution Approach 1:
The control circuit continuously monitors the capacitor voltage and compares it with a reference sinusoidal curve. Based on the deviation detected, the control circuit dynamically adjusts the switch-on time of the PFC switch to correct the voltage profile and minimize harmonic distortion in the current consumption.
Solution Approach 2:
The switch-on time of the PFC switch is made dynamic rather than fixed. The control circuit continuously varies the switch-on time based on the real-time capacitor voltage and the desired sinusoidal reference curve, enabling the circuit to adapt to changing voltage conditions and maintain sinusoidal current draw.
2Duration of action of stationary object
If the capacitor voltage drops after the rectified AC voltage peak, then the capacitor provides continuous power to the PFC circuit, but the current consumption occurs only in short sections and does not follow the sinusoidal mains AC voltage
Solution Approach 1:
The control circuit uses feedback from the capacitor voltage measurement to determine the precise timing and duration of switch-on periods. By comparing the actual capacitor voltage with the reference sinusoidal curve, the control circuit adjusts the switch-on time to ensure current draw follows the sinusoidal profile even when the capacitor voltage drops after the peak.
Solution Approach 2:
The control circuit proactively adjusts the switch-on time before the capacitor voltage drops significantly. By detecting the voltage trend and predicting the drop, the control circuit initiates switch-on periods at optimal times to recharge the capacitor in a controlled manner that maintains sinusoidal current consumption.
3Stability of the object's composition
If the switch-on time is extended to maintain capacitor voltage after the peak, then the voltage follows the reference curve better, but the current peak value increases
Solution Approach 1:
The switch-on time is dynamically adjusted based on the real-time voltage conditions. Rather than using a fixed extended switch-on time, the control circuit varies the duration continuously, extending it only when necessary to maintain the voltage profile and reducing it when the capacitor voltage is sufficient, thereby avoiding excessive current peaks.
Solution Approach 2:
The control circuit changes the switch-on time parameter dynamically based on the capacitor voltage and reference curve comparison. By adjusting this parameter in real-time rather than using a fixed value, the circuit maintains voltage profile accuracy while minimizing current peak values through optimal timing adjustments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively regulates the capacitor voltage to follow the desired sinusoidal curve, reducing harmonic distortion and current peaks, thereby improving the sinusoidal nature of current consumption and enhancing the overall performance of power factor correction.
Implementation Method 1
a rectifier (D2-D5), in particular a bridge rectifier
Implementation Method 2
a filter capacitor (C HF ), which is connected downstream of the rectifier
Implementation Method 3
an inductance or coil supplied with a rectified AC voltage is charged with energy or discharged by switching a controllable switch on and off
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to an actively pulsed power factor correction circuit (PFC) comprising an input to which an AC voltage can be supplied, a rectifier, a filter capacitor which is fed by the rectifier, and a switch which can be controlled by a control circuit in order to charge an inductance when turned on and to discharge when turned off. Said control circuit is designed to measure a capacitor voltage by means of the filter capacitor and to modify the length of time the circuit is switched on dependent on the measurement of the capacitor voltage.