Multilevel Converter Voltage Balancing via Distributed Control
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Solution Overview
Problem
Existing multilevel converters require complex control mechanisms and direct connections for each sub-module, leading to increased production costs and complexity, while also facing challenges in balancing capacitor voltages without knowing the direction of current flow.
Innovation Solution
The multilevel converter design groups sub-modules into multi-modules, where one switch of each sub-module is off during charging and discharging phases, with a control device monitoring capacitor voltages and implementing blocking periods to balance voltages, reducing the need for direct central device connections and simplifying control by using interposed control devices within multi-modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the central device controls all sub modules directly, then precise control is achieved, but the device complexity and production costs increase
Solution Approach 1:
The control system is segmented into a central device and distributed control devices, where each control device manages a specific multi module. This segmentation reduces the complexity of the central device while maintaining precise control through localized control intelligence.
Solution Approach 2:
Distributed control devices act as intermediaries between the central device and the sub modules. These intermediaries receive control signals from the central device and execute the control operations locally, reducing the direct control burden on the central device while maintaining precise control over the sub modules.
2Stability of the object's composition
If capacitor voltages are balanced by controlling all sub modules individually, then voltage balance is achieved, but the control complexity and number of control lines increase
Solution Approach 1:
The voltage balancing control is segmented and distributed to local control devices associated with each multi module. Each control device independently monitors and balances the capacitor voltages within its assigned multi module, eliminating the need for complex centralized control of all sub modules and reducing the number of control lines required.
3Ease of operation
If blocking periods are applied to balance capacitor voltages, then voltage balancing is simplified and does not require current direction measurement, but the switching complexity increases
Solution Approach 1:
The system uses self-service voltage balancing through blocking periods, where the control device automatically balances capacitor voltages by selectively blocking charge transfer to or from specific capacitors. This self-balancing mechanism eliminates the need for complex current direction measurement and switching operations, as the blocking periods inherently regulate voltage without requiring active switching control.
Data Source
AI summary
A multilevel converter has a central device for controlling operations and a plurality of series-connected sub modules that each has a first switch, a second switch, and a capacitor. At least two of the sub modules form a multi module, wherein, in charging phases and in discharging phases of the multi module, one of the switches of each sub module is switched off and the other switch of each sub module is switched on. The multi module has a control device that is connected to the central device and undertakes control of the sub modules of the multi module on the basis of control signals from the central device. The control device is configured such that it monitors the capacitor voltages of the sub modules and, in the event of an imbalance in the capacitor voltages, brings about balancing.