Switching Power Supply THD Reduction via Inductor Current Segmentation
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Solution Overview
Problem
Switching power supplies face challenges in reducing total harmonic distortion (THD) due to non-linear relationships between AC input voltage and inductor current, making it difficult to achieve desired THD levels and minimize losses in power equipment.
Innovation Solution
A method and apparatus that acquire first and second average inductor currents during successive conduction times in a switching cycle, with a regulation circuit adjusting the second conduction time based on the difference between these averages to ensure the average inductor current over the entire switching cycle follows the AC input voltage, using a combination of constant on-time control and conduction compensation control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional switching power supply control is used, then the power supply can operate with simple control circuitry, but the total harmonic distortion (THD) increases and performance deteriorates
Solution Approach 1:
The control method segments the switching cycle into multiple intervals (first conduction time, second conduction time, off time) and independently controls the inductor current in each interval. By dividing the control into discrete time segments with specific current targets, the system achieves precise THD reduction without requiring complex continuous control circuitry
Solution Approach 2:
The control circuit employs feedback mechanisms where the controller determines target inductor currents based on rectified AC input voltage and compares actual current against targets. Compensation currents are generated based on detected deviations, creating a closed-loop feedback system that reduces THD while maintaining manageable circuit complexity
2Manufacturing precision
If the inductor current is allowed to vary freely during switching cycles, then the control circuit remains simple, but the average inductor current does not follow the AC input voltage resulting in high THD
Solution Approach 1:
The controller pre-determines target inductor currents for each switching interval based on the rectified AC input voltage before the switching cycle begins. By establishing these targets in advance and programming the compensation current accordingly, the system ensures the inductor current follows the AC voltage waveform without requiring complex real-time adjustment mechanisms
Solution Approach 2:
The control system dynamically adjusts the compensation current waveform based on the varying AC input voltage characteristics. The controller modifies the target inductor current and compensation current in real-time according to the instantaneous AC voltage, enabling adaptive current waveform control that maintains accuracy across different operating conditions
3Loss of energy
If constant on-time control is used, then switching losses are reduced, but the inductor current waveform becomes distorted during off-time causing increased THD
Solution Approach 1:
The control method applies different current control characteristics to different time intervals within the switching cycle. During the first conduction time, the system maintains constant on-time for efficient switching, while during the second conduction time and off-time, it applies specific compensation currents to correct waveform distortion. This localized quality approach allows switching loss reduction while maintaining overall current waveform linearity
Solution Approach 2:
The invention converts the harmful effect of constant on-time control (which causes current distortion during off-time) into a benefit by deliberately programming compensation currents during the second conduction time and off-time intervals. The controller uses this otherwise problematic period to actively correct the inductor current waveform, transforming the distortion issue into an opportunity for THD reduction
Data Source
AI summary
A method of reducing THD can include: acquiring a first average inductor current during a first conduction time of a main power transistor of a power converter in a switching cycle; acquiring a second average inductor current during a second conduction time and an off time of the main power transistor in the switching cycle; and adjusting the second conduction time of the main power transistor in accordance with a difference between the first and second average inductor currents, where the first and second conduction times are successive.