AC-DC Power Converter Control Method for Harmonic Elimination
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Solution Overview
Problem
AC-DC power converters, particularly flyback converters, face challenges in maintaining a high power factor and reducing harmonic effects on the input current due to branch currents from filter capacitors, leading to inefficiencies and low power factor when loads are light.
Innovation Solution
The implementation of a control method that generates a second converting current with the same absolute value as the first branch current, using a triangular wave signal to adjust the conduction time of the power switching device, thereby summing the conduction times to eliminate harmonic effects and improve the power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter capacitor is used in the AC-DC power converter, then the output voltage can be maintained, but harmonic effects on the input current increase and power factor decreases
Solution Approach 1:
The patent segments the input current into two separate branch currents: one flowing through the filter capacitor and another through the power converting circuit. By independently controlling these two branches, the system can maintain the filtering function while compensating for harmonic effects. The power converting circuit generates a compensating current that counteracts the harmonic distortion caused by the capacitor branch, thus resolving the contradiction between output stability and input current quality.
Solution Approach 2:
The patent employs a composite control strategy that combines feedback control (for output voltage regulation) with feedforward control (for power factor correction). The control circuit processes both the output feedback signal and the input current signal simultaneously, creating a composite control signal that achieves dual objectives: maintaining output stability while eliminating harmonic effects on input current.
2Device complexity
If conventional control methods are used, then the circuit structure remains simple, but power factor is low and harmonic effects increase under light loads
Solution Approach 1:
The patent designs the power converting circuit to perform multiple functions simultaneously: power conversion, input current shaping, and power factor correction. By making the circuit multi-functional, the system achieves high power factor and low harmonic distortion without adding separate dedicated circuits, thus maintaining relatively simple overall structure while solving the light-load performance issues.
Solution Approach 2:
The patent implements a feedback control mechanism where the control circuit continuously monitors the input current and output voltage, then adjusts the switching duty cycle accordingly. This feedback loop enables the system to dynamically compensate for harmonic effects and maintain high power factor across different load conditions, including light loads, without requiring complex circuit modifications.
Data Source
AI summary
In one embodiment, a method of controlling an AC-DC power converter, can include: (i) receiving, by a filter capacitor, a first branch current from an input current of the AC-DC power converter; (ii) receiving, by a power converting circuit, a second branch current from the input current; (iii) receiving, by the power converting circuit, a feedback signal that represents an output signal of the power converting circuit, and a triangular wave signal that is determined by the first branch current; (iv) generating a first conduction time based on the feedback signal such that the power converting circuit produces a first converting current; and (v) generating a second conduction time based on the triangular wave signal such that the power converting circuit produces a second converting current having a same absolute value as the first branch current.