Modular Multi-Level Power Converter Energy Fluctuation Control

Solution Overview

Problem

Modular multilevel power converters require large capacitances in bridge modules, leading to significant construction volume, weight, and cost due to energy fluctuations, and existing control methods do not efficiently minimize these fluctuations.

Innovation Solution

A method that uses two-point control and modulation AC voltage with a higher frequency than the output frequency to control the switching times of power semiconductors, generating a circulating current to minimize energy variation, allowing for asymmetric dimensioning of power semiconductors and reducing necessary capacitances by a factor of 20 to 200.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If large capacitances are used in bridge modules to handle energy fluctuations, then the converter can operate reliably, but the construction volume, weight, and cost increase significantly

Engineering Contradiction:

Improveconverter operation reliabilityVSAvoidconverter weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent changes the operating parameters by introducing a circulating current that actively compensates for energy fluctuations. By controlling the switching times of power semiconductors to generate this circulating current, the system maintains capacitor voltages within permissible ranges without requiring oversized capacitors, thus reducing converter weight while maintaining reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a control mechanism that monitors capacitor voltages and adjusts the switching times of power semiconductors accordingly. This feedback control generates a circulating current that compensates for energy fluctuations in real-time, allowing the system to maintain reliable operation with smaller capacitances

Inventive Principle:

Principle #23Feedback

2Reliability

If large capacitances are used in bridge modules to handle energy fluctuations, then the converter can operate reliably, but the construction volume increases

Engineering Contradiction:

Improveconverter operation reliabilityVSAvoidconverter volume

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The patent changes the operating parameters by introducing a circulating current that actively compensates for energy fluctuations. By controlling the switching times of power semiconductors to generate this circulating current, the system maintains capacitor voltages within permissible ranges without requiring oversized capacitors, thus reducing converter volume while maintaining reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a control mechanism that monitors capacitor voltages and adjusts the switching times of power semiconductors accordingly. This feedback control generates a circulating current that compensates for energy fluctuations in real-time, allowing the system to maintain reliable operation with smaller capacitances

Inventive Principle:

Principle #23Feedback

3Device complexity

If traditional switching control is used, then the converter structure is simple, but energy fluctuations cause large capacitance requirements

Engineering Contradiction:

Improveconverter structure complexityVSAvoidcapacitance quantity

Core Design Contradiction:

Device complexityVSQuantity of substance

Solution Approach 1:

The patent implements a control mechanism that monitors capacitor voltages and adjusts the switching times of power semiconductors accordingly. This feedback control generates a circulating current that compensates for energy fluctuations in real-time, allowing the system to maintain reliable operation with smaller capacitances

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces a periodic circulating current with modulation frequency higher than the output frequency. This periodic action equalizes energy distribution among bridge modules and compensates for energy fluctuations, reducing the capacitance requirements while adding a controlled layer of complexity to the switching pattern

Inventive Principle:

Principle #19Periodic action

Data Source

PatentEP3353885B1Method for operating a modular multi-level power converter, modular multi-level power converter, and computer program

Publication Date: 2021.04.28 GOTTFRIED WILHELM LEIBNIZ UNIV HANNOVER

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AI summary

The invention relates to a method for operating a modular multi-level power converter having a plurality of power converter branches in each of which series circuits of bridge modules are arranged, wherein the bridge modules each have a bridge circuit in the form of a half-bridge or a full-bridge of power semiconductors and at least one capacitor which can be connected via the bridge circuit, wherein the method provides an output AC voltage at an output frequency on an output side of the power converter, wherein the desired temporal amplitude profile of the output AC voltage of the power converter is synthesized with a modulation frequency by means of a modulation AC voltage produced by the bridge modules of one or more power converter branches, which modulation frequency is higher than the output frequency, wherein the modulation AC voltage alternately exceeds and falls below the output AC voltage in time with the modulation frequency, and an energy controller assigned to a power converter branch in each case controls the switching times of the power semiconductors of the bridge modules in this power converter branch with the control objective of minimizing the energy variation of the power converter branch. The invention also relates to a modular multi-level power converter designed in this manner and to a computer program having program code means set up to carry out a method of the type mentioned above.