Multilevel Converter Sub-Module Switching Distribution Control

Solution Overview

Problem

Multilevel converter systems face inefficiencies in voltage balancing, leading to excessive switching in one sub-module, heat loss, and reduced lifespan due to unoptimized switching and capacitance requirements.

Innovation Solution

A method for controlling multilevel converters by detecting modulation states and current directions, grouping sub-modules, and adjusting their states to evenly distribute switchings, thereby optimizing switching and capacitance usage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If voltage balancing is performed by selecting sub-modules with highest or lowest voltage according to arm current, then voltage distribution among sub-modules is equalized, but switching operations concentrate on specific sub-modules leading to excessive heat loss and reduced lifespan

Engineering Contradiction:

Improvevoltage distribution uniformityVSAvoidheat loss from concentrated switching

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The control method uses feedback from detecting the number of switching operations for each sub-module and dynamically adjusts selection criteria. When a sub-module reaches a predetermined switching count, the controller modifies its selection logic to avoid further switching on that module, thereby distributing switching operations evenly and reducing heat loss while maintaining voltage balance through continuous monitoring and adjustment

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention changes the selection parameter from purely voltage-based (highest/lowest voltage) to a composite parameter that includes both voltage level and switching operation count. This parameter change allows the system to select sub-modules based on both voltage balance requirements and switching distribution requirements, thereby reducing concentrated switching and heat loss while maintaining voltage uniformity

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If sorting operation compares voltage values for all sub-modules to arrange them in order, then voltage balance is achieved, but computational complexity and control difficulty increase

Engineering Contradiction:

Improvevoltage balanceVSAvoidcontrol algorithm complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The control method segments the sub-module selection process into two independent stages: first detecting the number of switching operations for each sub-module, then using this count information to guide voltage-based selection. This segmentation avoids the need for complete sorting of all sub-modules by voltage, reducing computational complexity while maintaining voltage balance through the two-stage approach

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention performs preliminary detection of switching operation counts for all sub-modules before conducting voltage-based selection. This preliminary action provides pre-computed information that simplifies the subsequent selection process, eliminating the need for complex real-time sorting operations and reducing overall control algorithm complexity

Inventive Principle:

Principle #10Preliminary action

3Stability of the object's composition

If sub-modules are selected based on charging and discharging requirements, then voltage balance is maintained, but switching operations become unbalanced across sub-modules requiring more capacitance

Engineering Contradiction:

Improvevoltage balanceVSAvoidcapacitance requirement

Core Design Contradiction:

Stability of the object's compositionVSQuantity of substance

Solution Approach 1:

The control method uses feedback from detecting the number of switching operations for each sub-module and dynamically adjusts selection criteria. When a sub-module reaches a predetermined switching count, the controller modifies its selection logic to avoid further switching on that module, thereby distributing switching operations evenly and reducing heat loss while maintaining voltage balance through continuous monitoring and adjustment

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention changes the selection parameter from purely voltage-based (highest/lowest voltage) to a composite parameter that includes both voltage level and switching operation count. This parameter change allows the system to select sub-modules based on both voltage balance requirements and switching distribution requirements, thereby reducing concentrated switching and heat loss while maintaining voltage uniformity

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9455618B2Method for controlling multilevel converter

Publication Date: 2016.09.27 LSIS CO LTD

AI summary

The present disclosure provides a method for controlling a multilevel converter, the method including, detecting modulation state values and current directions of sub-modules, and designating, by one sub-module, an average number of switching for each period of an output waveform, wherein the step of designating the average number of switching includes, grouping the sub-modules according to being in ON state or in OFF state, comparing the number of sub-modules in previous ON state and the number of sub-modules in OFF state to obtain a difference therebetween, and changing a state as much as the difference, comparing a sub-module of ON state in charged state and in discharged state with a sub-module of OFF state, and changing the compared states of sub-modules of ON state and OFF state.