Multilevel Voltage Source Converter Topology
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Solution Overview
Problem
Conventional voltage source converters experience high losses, electromagnetic interference, and complex designs due to high switching frequencies and the need for harmonic filtering, especially when converting between AC and DC power in power transmission networks.
Innovation Solution
A voltage source converter configuration that includes a multilevel converter block in one limb portion and a switching block in the other, allowing for reduced switching frequency and eliminating the need for harmonic filtering, using a multilevel converter block to control AC and DC waveforms and enabling high-quality power transfer with reduced component count and size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high switching frequency is used in conventional voltage source converters, then power conversion capability is improved, but switching losses and electromagnetic interference increase
Solution Approach 1:
The converter is divided into multiple converter cells connected in series, with each cell contributing a portion of the total voltage. This segmentation allows lower switching frequencies in each cell while achieving the required power conversion capability at the system level, thereby reducing switching losses and electromagnetic interference.
Solution Approach 2:
The patent transitions from conventional two-level converter topology to multilevel converter topology, adding voltage levels as a new dimension. This enables the converter to operate at lower switching frequencies while maintaining power conversion capability, as the voltage steps are smaller and more gradual across multiple levels.
2Power
If high switching frequency is used in conventional voltage source converters, then power conversion capability is improved, but electromagnetic interference increases
Solution Approach 1:
By segmenting the converter into multiple cells with incremental voltage contributions, the rate of change of voltage (dv/dt) in each cell is reduced. This segmentation effectively lowers electromagnetic interference while preserving the overall power conversion capability of the system.
Solution Approach 2:
The multilevel topology introduces additional voltage levels, creating a more gradual voltage transition profile. This dimensional change in the voltage waveform reduces high-frequency harmonics and electromagnetic interference while maintaining the required power conversion performance.
3Loss of energy
If multilevel converter arrangement is used, then switching losses are reduced, but device complexity and equipment size increase
Solution Approach 1:
The patent uses identical or standardized converter cell designs that can be replicated and connected in series. This copying approach reduces design complexity by allowing the use of modular, proven cell architectures rather than designing a completely new complex system, while still achieving reduced switching losses through the multilevel configuration.
4Stress or pressure
If high number of converter cells are used, then voltage rating requirements are met, but equipment size and weight increase
Solution Approach 1:
The converter voltage rating is achieved through segmentation into multiple series-connected cells, where each cell operates at a lower voltage level. This segmentation allows the use of smaller, lighter components in each cell compared to a single high-voltage converter, reducing overall equipment weight while meeting the required voltage rating.
Data Source
Figure 1a~1b
Figure 1c
Figure 2~3a
AI summary
A voltage source converter (30) comprises: first and second DC terminals (32,34) for connection to a DC electrical network (44); and a converter limb (36) directly connected between the first and second DC terminals (32,34), the converter limb (36) including: an AC terminal (42) for connection to an AC electrical network (46); a first limb portion (38) directly connected between the first DC terminal (32) and the AC terminal (42); and a second limb portion (40) directly connected between the second DC terminal (34) and the AC terminal (42), wherein only one of the first and second limb portions (38,40) includes a multilevel converter block (52), the other of the first and second limb portions (38,40) includes a switching block (48), the switching block (48) is switchable to selectively permit current flow in at least one direction in the corresponding limb portion (38) and inhibit current flow in at least one direction in the corresponding limb portion (38), and at least one of the first and second limb portions (38,40) is controllable to control the configuration of an AC voltage waveform at the AC terminal (42).