Multilevel Converter Switching Stage for Wind Turbines

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Solution Overview

Problem

Existing multilevel energy conversion circuits for wind generators face challenges in minimizing conduction losses while maintaining a compact, cost-effective design, often resulting in overvoltages and complex electromechanical designs due to the need for numerous semiconductors and capacitors.

Innovation Solution

A switching stage with a reduced number and size of capacitors, fixed switch voltages, and lower overvoltages is integrated into the energy conversion circuit, utilizing a bus with multiple capacitors and switches to achieve n output voltage levels for DC/AC and AC/DC conversions, simplifying design and control while reducing semiconductor stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the number of voltage levels is increased to reduce conduction losses and improve current quality, then the handled power and current quality increase, but the converter size and cost increase due to more capacitors and semiconductors

Engineering Contradiction:

Improveconduction lossesVSAvoidconverter size

Core Design Contradiction:

Loss of energyVSVolume of stationary object

Solution Approach 1:

The converter is divided into multiple identical cells, each contributing to the overall voltage levels. This modular segmentation allows the system to achieve high voltage levels without proportionally increasing the size of individual components, as each cell uses a standardized set of capacitors and semiconductors.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each cell in the converter is designed to be universal and interchangeable, performing the same function while contributing to the cumulative voltage output. This multi-functionality allows the same component design to be replicated across multiple cells, optimizing the balance between voltage level achievement and component utilization efficiency.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Power

If more capacitors and semiconductors are added to achieve higher voltage levels, then the output voltage and power increase, but the device complexity and manufacturing cost increase

Engineering Contradiction:

Improveoutput powerVSAvoidconverter complexity

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The converter architecture segments the power handling function across multiple identical cells, where each cell processes a portion of the total power. This segmentation maintains manageable complexity within each cell while achieving high total power output through parallel operation of multiple cells.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Multiple identical cells are merged in parallel to achieve the desired power level and voltage output. The merging of standardized cells simplifies the overall system design compared to using a single complex high-power converter, as each cell can be independently optimized and manufactured.

Inventive Principle:

Principle #5Merging (Combining)

3Power

If series-connected cells are used to increase voltage levels, then the available voltage levels increase, but the control complexity over voltage distribution among semiconductors increases

Engineering Contradiction:

Improvevoltage levelsVSAvoidvoltage distribution control

Core Design Contradiction:

PowerVSEase of operation

Solution Approach 1:

The voltage distribution control problem is segmented by assigning independent control to each cell. This allows voltage balancing to be handled at the cell level rather than requiring complex system-wide control, simplifying the overall voltage distribution management while maintaining high voltage levels through series connection of controlled cells.

Inventive Principle:

Principle #1Segmentation

4Reliability

If additional voltage limiting circuits and semiconductors are added to mitigate overvoltages, then semiconductor reliability improves, but the converter size and cost increase

Engineering Contradiction:

Improvesemiconductor reliabilityVSAvoidconverter size

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The capacitor bridges are designed to inherently limit overvoltages during semiconductor switching by providing pre-configured charge storage and discharge paths. This beforehand cushioning effect protects semiconductors from voltage spikes without requiring additional active protection circuits, maintaining reliability while avoiding extra volume from protective components.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS9660553B2Switching stage, energy conversion circuit, and conversion stage for wind turbines comprising the energy conversion circuit

Publication Date: 2017.05.23 INGETEAM POWER TECH

AI summary

The present invention relates to an energy conversion circuit comprising a switching stage with a positive DC voltage terminal (1), a negative DC voltage terminal (3), m−1 intermediate DC voltage terminals (2) m DC bus capacitors (5); and p linked cells consisting of m+1 switches (9) and at least one capacitor (10), connecting cell 1 to the positive DC voltage terminal (1), negative DC voltage terminals (3) and intermediate DC voltage terminals (2); and a multilevel converter, the output of which is connected to the AC voltage terminal (4), with a positive voltage terminal (12) and a negative voltage terminal (14) of the multilevel converter and m−1 intermediate voltage terminals of the multilevel converter (13), which are connected to the positive output terminal of the switching stage (6), to the negative output terminal of the switching stage (8), and to the m−1 intermediate output terminals of the switching stage (7), respectively.