Multilevel Voltage Source Converter Submodule Design
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Solution Overview
Problem
Existing power electronic converters face challenges in reducing harmonic distortion and switching stress, which limits their efficiency and increases costs due to high semiconductor losses and insulation requirements.
Innovation Solution
A power electronic converter design featuring phase legs with series-connected variable voltage sources and submodules, each comprising power electronic switches in parallel with capacitors, and an auxiliary reactor with switchable auxiliary power electronic switches, reducing switching stress and insulation demands by allowing for multilevel output and soft switching techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional voltage source converters are used to reduce harmonic distortion, then output quality improves, but switching stress on semiconductors increases leading to higher losses
Solution Approach 1:
The voltage source is divided into multiple submodules (first and second submodules) connected in series, each capable of independent voltage level control. This segmentation allows the converter to achieve multilevel output voltage, reducing harmonic distortion while distributing switching stress across multiple devices, thereby lowering individual semiconductor losses.
Solution Approach 2:
The invention changes the voltage level parameter by providing multiple discrete voltage levels (multilevel output) instead of a single bipolar level. This parameter change reduces the voltage stress on individual switches and allows for softer switching transitions, decreasing switching losses while maintaining effective harmonic reduction.
2Object-generated harmful factors
If multilevel converter topologies are implemented to reduce harmonic distortion, then output quality improves, but device complexity and cost increase
Solution Approach 1:
The converter is segmented into modular submodules that can be independently controlled. Each submodule contains standard components (switches, capacitors, reactors), and the modular structure simplifies the control strategy compared to traditional multilevel topologies, reducing overall system complexity while achieving multilevel output for harmonic reduction.
Solution Approach 2:
The auxiliary reactor serves multiple functions: it enables soft switching for the main power switches, provides voltage clamping during transitions, and assists in achieving multilevel output. This multi-functionality reduces the need for additional dedicated components, thereby reducing device complexity and cost.
3Strength
If higher blocking voltage devices are used to handle voltage stress, then voltage capability improves, but device cost and availability decrease
Solution Approach 1:
The high voltage capability is achieved by segmenting the voltage blocking requirement across multiple submodules connected in series. Each submodule uses switches with lower blocking voltage ratings, but the series connection of submodules achieves the required total blocking voltage. This segmentation makes the system easier to manufacture with readily available semiconductor devices.
Solution Approach 2:
The invention changes the voltage distribution parameter by using multiple voltage levels instead of a single high voltage level. This allows the use of lower-voltage-rated switches in each submodule, improving device availability and ease of manufacture while maintaining the required overall voltage capability through series connection of submodules.
4Speed
If fast switching is used to improve converter response, then dynamic performance improves, but insulation stress on connected equipment increases
Solution Approach 1:
The invention changes the voltage transition parameter by providing multiple intermediate voltage levels between the minimum and maximum voltage states. This results in slower voltage slopes (dv/dt) during switching transitions compared to conventional two-level converters, reducing insulation stress on connected equipment while maintaining acceptable dynamic response through coordinated switching of multiple submodules.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design reduces semiconductor switching stress, lowers losses, enables the use of high-blocking-voltage devices, decreases the number of submodules needed, and reduces insulation stress on connected equipment, thereby lowering overall costs and improving efficiency.
Implementation Method 1
Each submodule comprises an auxiliary reactor. A first terminal of the auxiliary reactor is connected to the inner connection point of the two power electronic switches and a second terminal of the auxiliary reactor is connected via at least one auxiliary power electronic switch to a terminal of the at least one capacitor.
Data Source
Figure 1~2
Figure 3
AI summary
In a device for converting a DC voltage into an AC voltage of variable amplitude and frequency and vice versa at least one phase leg comprises a first and a second variable voltage source connected in series between two DC terminals (12, 13), where each of the voltage sources comprises at least a first and a second submodule in series-connection. Each submodule comprises a series-connection of two power electronic switches (1) connected in parallel with at least one capacitor (8; 10) and is connected via the inner (4) and one of the two outer (5, 6) connection points of its two power electronic switches (1) to either a neighbouring submodule or to one the two DC terminals. In addition, each submodule comprises an auxiliary reactor (7) whose first terminal is connected to the inner connection point (4) of the two power electronic switches (1) and whose second terminal is connected via at least one auxiliary power electronic switch (11) to a terminal (5, 6, 9) of the at least one capacitor (8; 10).