Multilevel Voltage Source Converter Auxiliary Waveform Synthesis
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Solution Overview
Problem
Existing multilevel voltage source converters for HVDC power transmission and reactive power compensation face challenges such as high losses, electromagnetic interference, complex design, and expensive equipment due to the need for complex gate drives and large passive components, as well as high harmonic distortion and costly fibre-optic communication requirements.
Innovation Solution
A multilevel voltage source converter with an auxiliary converter acting as a waveform synthesizer to modify the DC voltage, allowing for synchronized switching of semiconductor switches and reducing harmonic distortion, which minimizes switching losses and fibre-optic communication needs, using chain-link or diode-clamped multilevel converters to produce near-perfect sine-waves with minimal harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If series strings of IGBT devices are switched at high voltage to control harmonic currents, then reactive power control capability is improved, but switching losses and electromagnetic interference increase significantly
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitor banks to specific voltage levels before switching operations. The capacitor banks are charged to voltages that match the expected switching requirements, allowing IGBT devices to switch at lower voltage stress while maintaining the ability to synthesize required voltage waveforms. This reduces switching losses and electromagnetic interference while preserving reactive power control capability.
Solution Approach 2:
The patent introduces capacitor banks as intermediary energy storage elements between the DC source and the IGBT switching network. These capacitors act as buffers that can be pre-charged to appropriate voltage levels, mediating the voltage stress on IGBT devices during switching operations. This intermediary approach enables controlled voltage synthesis without requiring all IGBTs to switch simultaneously at full voltage, thereby reducing switching losses and EMI.
2Measurement precision
If multiple fibre-optic communication channels are used for controlling individual cells, then control precision is improved, but system complexity and cost increase
Solution Approach 1:
The patent applies universality by designing a unified control architecture where a single fibre-optic communication channel controls multiple capacitor banks and IGBT cells. The control system uses universal control algorithms that can manage the entire converter assembly through one communication interface, eliminating the need for individual communication channels for each cell. This reduces system complexity while maintaining control precision through coordinated control of the modular components.
3Reliability
If large DC link capacitors and DC side reactors are installed in each cell, then reliability is improved, but equipment size, weight, and cost increase significantly
Solution Approach 1:
The patent applies merging by consolidating the energy storage function into shared DC link capacitors located at the DC input side, rather than requiring large capacitors in each individual cell. The capacitor banks are shared resources that serve multiple IGBT cells simultaneously. This combining approach maintains the necessary energy storage capacity for reliable operation while dramatically reducing the total amount of capacitive and inductive material required, thereby reducing weight, size, and cost.
Data Source
AI summary
A multilevel voltage source converter for high voltage DC power transmission and reactive power compensation. The voltage source converter includes at least one phase element including a plurality of semiconductor switches to interconnect a DC voltage and an AC voltage. The voltage source converter also includes at least one auxiliary converter to act as a waveform synthesizer to modify the DC voltage presented to the DC side of the phase element.