Current Reference SHCM-PWM for Harmonic Mitigation
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Solution Overview
Problem
Conventional power modulation techniques for grid-connected cascaded H-bridge multilevel rectifiers, such as SHE-PWM and SHM-PWM, are limited in their ability to mitigate current harmonics due to grid voltage harmonics and require large coupling inductances, leading to increased costs and sizes of passive filters.
Innovation Solution
The implementation of selective harmonic current mitigation pulse width modulation (SHCM-PWM) methods, which use current references instead of voltage references to calculate switching angles, allowing for reduced coupling inductances and effective mitigation of higher-order current harmonics within the entire harmonic spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional SHE-PWM or SHM-PWM techniques are used, then voltage references are used to calculate switching angles, but current harmonics cannot be effectively mitigated and large coupling inductances are required
Solution Approach 1:
The patent changes the fundamental parameter used for PWM calculation from voltage references to current references. This parameter change enables direct control and mitigation of current harmonics across the entire harmonic spectrum, eliminating the need for large coupling inductances that were previously required to filter these harmonics.
Solution Approach 2:
The patent replaces the mechanical/filter-based harmonic mitigation approach (large coupling inductances) with a control-based approach (current reference PWM). This substitution eliminates the need for bulky passive filter components by using intelligent switching control to directly mitigate current harmonics at their source.
2Object-affected harmful factors
If conventional SHE-PWM techniques are used, then switching frequencies must be high to meet harmonic requirements, but this increases switching losses and reduces efficiency
Solution Approach 1:
By changing from voltage-based to current-based reference PWM, the patent achieves effective harmonic mitigation at lower switching frequencies. The current reference method directly targets harmonic current components, allowing sufficient harmonic control without the need for high-frequency switching that would otherwise be required.
Solution Approach 2:
The patent converts the harmful effect of low switching frequency (which would normally result in poor harmonic control) into a benefit by using current references. The current-based control method is particularly effective at lower frequencies, turning what would be a disadvantage into an advantage for reducing switching losses.
3Ease of manufacture
If voltage references are used for PWM calculation, then the method is simpler to implement, but it cannot satisfy current harmonic requirements and TDD across the entire harmonic spectrum
Solution Approach 1:
The patent changes the reference parameter from voltage to current, which fundamentally improves harmonic control capability. While current sensing and processing adds some complexity, the overall system becomes more effective at meeting harmonic requirements without requiring additional passive filter components, achieving a different kind of simplicity in meeting performance specifications.
Data Source
AI summary
Methods and apparatuses for selective harmonic current mitigation pulse width modulation (SHCM-PWM) are provided. Low switching frequencies can be utilized for grid connected cascaded H-bridge multilevel rectifiers to meet harmonic requirements within an extended harmonic spectrum. Instead of using voltage references to calculate switching angles for rectifiers as in conventional selective harmonic elimination-PWM (SHE-PWM) and selective harmonic mitigation-PWM (SHM-PWM), current references can be used to compensate for current harmonics and meet current harmonic requirements and total demand distortion (TDD) within the entire harmonic spectrum.