Cascaded H-Bridge Harmonic Injection for Smaller DC-Link Capacitors
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Solution Overview
Problem
Existing cascaded H-bridge power conversion apparatuses suffer from high-order voltage harmonics on the floating direct current side, which require large capacitors to filter, resulting in low power density and large volume.
Innovation Solution
A method for controlling a three-phase three-wire cascaded H-bridge power conversion apparatus that involves calculating specific current components and generating injection voltages with triple and quintuple frequencies to transfer and cancel double and quadruple frequency current components from the floating direct current side to the low-voltage direct current side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large capacitors are used to filter high-order voltage harmonics on the floating direct current side, then harmonic characteristics are improved, but power density decreases and volume increases
Solution Approach 1:
The patent extracts the harmful double frequency current component from the floating direct current side by calculating it separately and transferring it to the low-voltage direct current side through the dual active bridge converter, where it can be eliminated without requiring large filtering capacitors on the floating side
Solution Approach 2:
The dual active bridge converter acts as an intermediary device that receives the floating direct current side power and selectively transfers the double frequency current component to the low-voltage direct current side, enabling harmonic elimination without large capacitors
2Object-affected harmful factors
If capacitors are arranged in each stage to filter harmonics, then voltage harmonics are reduced, but device complexity increases
Solution Approach 1:
The patent merges the harmonic filtering function into the existing dual active bridge converter structure, which already performs power conversion. The converter is controlled to transfer double frequency current components to the low-voltage side, combining two functions into one device and eliminating the need for separate capacitors in each stage
Data Source
AI summary
A harmonic suppression method and apparatus for a three-phase three-wire cascaded power conversion apparatus is disclosed. The method can include: calculating a first current output from a full-bridge rectifier module to a floating direct current side, the first current being composed of a first current direct current component and a first current double frequency component; and generating a first injection voltage with a triple frequency, so as to inject the first injection voltage into the floating direct current side and transfer at least a portion of the first current double frequency component to a low-voltage direct current side, where total current on the floating direct current side is composed of the first current and a second current after the first injection voltage is injected, the second current is composed of a second current double frequency component and a second current quadruple frequency component, and the amplitude and the phase angle of the first injection voltage are configured so that the first and second current double frequency components are at least partially canceled. The method reduces the demand for capacitance on the floating direct current side of the power conversion apparatus, resulting in a significant increase in power density and high power conversion efficiency.