PFC Reference Sine Generation for Zero-Crossing Harmonic Control
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Solution Overview
Problem
Existing PFC controllers face challenges in generating a reference sine wave that accurately aligns input current and voltage waveforms, leading to inefficiencies and harmonic distortion, particularly near zero-crossing events, and require excessive power consumption and complexity.
Innovation Solution
A PFC controller that combines a divided reference signal with a synthesized reference signal, using a multiplexer to select between them based on current amplitude and zero-crossings, reducing harmonic distortion and improving power factor efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference sine wave is used to align input current and voltage waveforms, then power factor is increased, but harmonic distortion occurs particularly near zero-crossing events
Solution Approach 1:
The reference signal generation is segmented into two distinct sources: a divided reference signal for peak amplitude intervals and a synthesized reference signal for zero-crossing intervals. The multiplexer selectively switches between these two segments based on the current amplitude level, thereby avoiding harmonic distortion at zero-crossings while maintaining power factor correction effectiveness during peak intervals.
Solution Approach 2:
Different quality characteristics are applied to different intervals of the AC cycle. During peak amplitude intervals, the divided reference signal is used which provides accurate amplitude representation. During zero-crossing intervals, the synthesized reference signal is used which provides clean waveform generation without distortion. This local quality differentiation resolves the contradiction between power factor improvement and harmonic distortion reduction.
2Productivity
If a synthesized reference signal is generated using digital values, then operational efficiency is improved, but device complexity increases
Solution Approach 1:
The reference signal generation process is segmented into two paths: an analog division path for peak intervals and a digital synthesis path for zero-crossing intervals. This segmentation allows the system to use simpler analog circuitry for the majority of the AC cycle (peak intervals) while employing digital synthesis only when necessary (zero-crossing intervals), thereby balancing operational efficiency with device complexity.
Solution Approach 2:
The multiplexer periodically switches between the divided and synthesized reference signals based on the AC input signal's amplitude intervals. This periodic action ensures that the more complex synthesized signal is generated only during specific intervals (zero-crossings), reducing the overall computational burden and device complexity while maintaining operational efficiency during critical periods.
3Measurement precision
If the divided reference signal is used during peak amplitude intervals, then signal accuracy is maintained, but harmonic distortion occurs near zero-crossings
Solution Approach 1:
The patent applies different signal quality characteristics to different intervals of the AC cycle. During peak amplitude intervals, the divided reference signal is used which maintains high signal accuracy for power factor correction. During zero-crossing intervals, the synthesized reference signal is used which eliminates harmonic distortion. This local quality differentiation resolves the contradiction between signal accuracy and harmonic distortion reduction.
Solution Approach 2:
The multiplexer acts as an intermediary that selectively routes between the divided reference signal and the synthesized reference signal based on the current amplitude level. This intermediary function allows the system to transition smoothly between different signal sources, maintaining signal accuracy during peak intervals while avoiding harmonic distortion during zero-crossing intervals.
Data Source
AI summary
A power factor correction (PFC) controller for a PFC switching power supply is disclosed. The PFC controller includes an AC sense terminal, a DC sense terminal, and a reference signal generator coupled to the AC sense terminal. The reference signal generator is configured to receive a divided reference signal generated based on a modified version of an AC input signal and generate a synthesized reference signal using information indicative of an amplitude and a frequency of the divided reference signal. The reference signal generator is further configured to select one of the divided and synthesized reference signals as an output reference signal based on a current amplitude of the divided reference signal. The PFC controller is configured to, based on the output reference signal and a DC voltage sensed on the DC sense terminal, regulate output power provided to a downstream power converter coupled to the PFC switching power supply.