Bridge Rectifier Switch Timing for Even-Harmonic Suppression
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Solution Overview
Problem
Existing solutions to suppress even-order harmonics in supply voltage for AC-DC converters are costly and introduce high-frequency components, and traditional Total Harmonic Distortion (THD) metrics fail to account for phase angle effects on DC bus capacitor current.
Innovation Solution
A control method for semiconductor switches in a bridge rectifier that estimates even-order harmonics' magnitude and phase angle, triggering upper and lower leg switches at specific angles to suppress these harmonics, using Asymmetry Factor (AF) and Zero Cross Detector (ZCD) thresholds to minimize ripple current and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If existing solutions (Electronic Inductor, modified DVR, Active front end ASD) are used to suppress even harmonics, then the effect of even harmonics on the drive is suppressed, but additional costly components (switches, gate drivers, sensors, transformers) are required and high frequency switching components are introduced in the line current
Solution Approach 1:
The patent extracts and addresses only the specific problem of even-order harmonics (2nd, 4th, 6th) rather than attempting to suppress all harmonics. By focusing on removing this specific harmful component through selective trigger angle adjustment, the solution avoids the complexity of comprehensive harmonic suppression systems while effectively addressing the dominant harmful factor.
Solution Approach 2:
The patent changes the trigger angles of the rectifier switches as a control parameter to suppress even harmonics. By adjusting the trigger angles differently for upper and lower leg switches based on detected even harmonic conditions, the system achieves harmonic suppression through parameter modification rather than adding physical filtering components.
2Measurement precision
If Traditional THD metric is used to assess harmonics, then harmonics magnitude is measured, but phase angle information is not captured and thus the effect on DC bus capacitor current is not accurately reflected
Solution Approach 1:
The patent introduces an intermediary measurement approach that detects even harmonic components and their phase angles in the supply voltage. This intermediary detection system provides the missing phase information that connects the voltage harmonics to their actual effect on capacitor current, enabling more precise control decisions.
Solution Approach 2:
The patent implements feedback by continuously monitoring the supply voltage for even harmonic content and using this information to dynamically adjust the switch trigger angles. The system measures the actual harmonic conditions and feeds this information back to the control logic, which then modifies the trigger angles to suppress the detected even harmonics.
Data Source
AI summary
The invention discloses systems (100) and methods (200, 300) for reducing the effect of even-order harmonics in supply voltage on the DC side components in AC-DC converters having any kind of controlled power electronic switches or their combinations. The method involves modifying the time of firing the various switches (112, 114) through a control logic arrives at through either measuring or estimating the DC bus voltage or the input AC voltage. The proposed control methods are useful in ASDs where full bridge configuration is used for AC to DC conversion. The proposed control may also be used in ASDs where a half bridge rectifier system is used. The proposed method reduces the stress on the DC bus capacitor and increases the lifetime of the capacitor. It further reduces the peak current through the device, which reduces stress on the rectifier components. It also reduces the Total Harmonic Distortion (THDi) of the line current.