Modular Multilevel Converter Analog Cell for Voltage Smoothing
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Solution Overview
Problem
Conventional modular multilevel converters require large arm inductances to achieve high output voltage quality, which limits switching frequency and regulator velocity, and results in increased switching losses.
Innovation Solution
Incorporating an analog cell with a passive device, such as a capacitor, connected in parallel to other submodules, allowing for higher switching frequencies in the analog cell while maintaining low switching frequencies in other submodules, thereby smoothing voltage transitions and minimizing arm inductances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If arm inductance is increased to improve output voltage quality, then output voltage quality is improved, but switching frequency and regulator velocity are reduced
Solution Approach 1:
The converter is divided into multiple submodules connected in series, with one submodule designated as an analog cell and others as digital cells. This segmentation allows different switching frequencies to be applied to different parts of the system, enabling high-frequency operation in the analog cell for voltage smoothing while maintaining lower switching frequencies in digital cells, thus resolving the contradiction between voltage quality and switching frequency.
Solution Approach 2:
Different submodules are assigned different functions and operating characteristics. The analog cell operates at high switching frequency specifically for smoothing voltage transitions, while other submodules operate at lower frequencies. This local differentiation of quality and function allows the system to achieve high output voltage quality without requiring all components to operate at high frequencies, thereby maintaining overall system efficiency.
2Manufacturing precision
If arm inductance is increased to smooth output voltage, then output voltage quality is improved, but switching losses increase
Solution Approach 1:
By segmenting the converter into analog and digital submodules, the system can concentrate high-frequency switching operations in the analog cell where they are most effective for voltage smoothing. Other submodules operate at lower frequencies, reducing their switching losses. This segmentation allows voltage quality improvement without proportionally increasing overall switching losses.
Solution Approach 2:
The system changes the operating parameters of different submodules - specifically the switching frequency - to optimize performance. The analog cell operates at high frequency for effective voltage smoothing, while digital cells operate at lower frequencies to minimize switching losses. This parameter differentiation resolves the contradiction between voltage quality and energy efficiency.
3Manufacturing precision
If switching frequency is increased to improve voltage smoothing, then output voltage quality is improved, but device complexity increases
Solution Approach 1:
The control system is segmented into different control strategies for analog and digital submodules. The analog cell uses continuous high-frequency switching for voltage smoothing, while digital cells use lower-frequency pulse-width modulation. This segmentation of control approaches simplifies the overall control architecture compared to uniformly high-frequency operation of all submodules.
Solution Approach 2:
The system employs dynamic switching frequency allocation where the analog cell operates at high frequency for voltage smoothing while digital cells operate at lower frequencies. This dynamic differentiation of operating parameters allows effective voltage control without requiring uniformly complex high-frequency control across all submodules, thereby reducing overall device complexity.
Data Source
AI summary
A current converter circuit in a modular multilevel topology includes an AC voltage terminal with a first phase terminal and a further voltage terminal with a plus and a minus terminal. The current converter circuit includes two arms, wherein the first arm connects the first phase terminal and the first terminal and the second arm the second phase terminal and the minus terminal. Each arm includes at least two submodules connected in series, wherein one of the at least two submodules is implemented as analog cell including a passive device as well as an electric circuit. The passive device is connected in parallel to the electric circuit and connected in series with respect to the other one of the at least two submodules.