UX-CELL Multilevel Converter Topology for Low-Harmonic Output
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Solution Overview
Problem
Conventional multilevel converters require a large number of switches and DC sources to achieve a sufficient number of voltage levels, leading to bulkiness and high manufacturing costs, and they generate negative harmonics that affect voltage and current in electric grids.
Innovation Solution
A multilevel power converter with a reduced number of components, utilizing a UX-CELL topology that includes a single DC source and capacitor, and controlled by a Model Predictive Control (MPC) method to produce multiple voltage levels without transformers, achieving up to twenty-three voltage levels with only twelve unipolar devices and four diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional multilevel converter topologies (Neutral Point Diode Clamped, Flying Capacitor, Cascaded H-Bridge) are used to reduce harmonics, then harmonic reduction is achieved, but the device becomes bulky and complex when the number of levels exceeds three due to large number of active and passive components
Solution Approach 1:
The converter is divided into modular units (first cell, second cell, intermediate cells) where each cell contains a limited number of switches and DC sources. This segmentation allows the system to achieve high voltage levels through series connection of multiple cells rather than using a single complex circuit with many components.
Solution Approach 2:
Multiple cells are combined in series to achieve the desired voltage levels. The intermediate cells connect the first and second cells, creating a unified multilevel converter structure that reduces total component count compared to conventional topologies while maintaining the ability to generate multiple voltage levels.
2Object-generated harmful factors
If the number of voltage levels is increased to reduce harmonics further, then harmonic reduction improves, but the number of switches and DC sources must be increased proportionally
Solution Approach 1:
Each cell in the converter serves multiple functions: it contributes to voltage level generation, harmonic reduction, and can be independently controlled. The intermediate cells particularly serve dual purposes by connecting the first and second cells while also contributing voltage levels, thereby reducing the total number of components needed.
Solution Approach 2:
The converter architecture transitions from a single-plane conventional topology to a multi-cell series connection structure. This dimensional change allows voltage levels to be accumulated through series connection of cells rather than adding more parallel branches, reducing the overall component count while achieving higher voltage levels.
3Device complexity
If conventional two-level or three-level inverters are used for renewable energy injection, then simplicity is maintained, but negative harmonics are generated that adversely affect voltage and current in distributed networks
Solution Approach 1:
The converter is segmented into multiple cells that can independently contribute to the output waveform. This segmentation enables the generation of a multilevel output with closer approximation to a perfect sine wave, thereby reducing negative harmonics while maintaining relatively simple individual cell structures.
Solution Approach 2:
The converter changes the voltage level parameters by providing multiple discrete voltage levels (five or seven levels) instead of conventional two or three levels. This parameter change in voltage level multiplication allows for better waveform synthesis with reduced harmonics while keeping the per-cell complexity manageable.
Data Source
AI summary
A multilevel power converter is provided. A first cell comprises a first switch and a second switch connectable to a load via a first terminal and connected in series on opposite poles of a DC source. A second cell comprises a third switch and a fourth switch connectable to the load via a second terminal and connected in series on opposite poles of a DC capacitor. An intermediate cell connects the first and second cells and comprises a fifth switch connected to positive poles of the source and the capacitor, a sixth switch connected to negative poles of the source and the capacitor, a seventh switch connected to the positive pole of the source and to the negative pole of the capacitor, and an eighth switch connected to the negative pole of the source and to the positive pole of the capacitor.