Multi-Level Power Converter Using Cascaded NPC and Capacitive Stages
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Solution Overview
Problem
Existing multi-level power converters face challenges in achieving high voltage levels without increasing the number of semiconductor switches, while maintaining cost-effectiveness, reliability, and minimizing spurious inductances and voltage constraints on switches.
Innovation Solution
A multi-level converter design that combines NPC-type cells and capacitive cells, with each arm comprising two stages connected in cascade, where the first stage consists of multiple elementary stages of rank one to n, and the second stage includes a floating capacitor cell, using identical energy storage devices and inductances to manage voltage and reduce switch stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the number of semiconductor switches is increased to achieve high voltage levels, then the voltage level is improved, but the cost and device complexity increase significantly
Solution Approach 1:
The converter is divided into multiple modular stages (first stage with elementary stages E11 to E1n, second stage with floating capacitor cell), where each stage contributes to the overall voltage multiplication. This segmentation allows achieving high voltage levels through cascaded modular units rather than using a single complex high-voltage switch configuration.
Solution Approach 2:
Elementary stages are nested in cascade configuration, with each elementary stage containing pairs of nested elementary base cells. The capacitive cells are nested between the NPC-type cells, creating a compact multi-level structure that achieves high voltage multiplication factor (n+1) while maintaining modularity and reducing overall system complexity.
2Device complexity
If the number of semiconductor switches is reduced to lower cost and complexity, then device complexity is improved, but the ability to achieve high voltage levels deteriorates
Solution Approach 1:
Capacitive cells act as intermediary energy storage elements between the NPC-type cells, enabling voltage multiplication without requiring additional semiconductor switches. The capacitors store and transfer energy between stages, allowing the system to achieve high voltage levels through passive energy storage rather than active switching multiplication.
Solution Approach 2:
The invention changes the operating parameters by using identical energy storage devices with standardized voltage ratings across all capacitive cells. By configuring these standard capacitors in series within each capacitive cell and cascading multiple capacitive cells, the system achieves higher overall voltage levels while maintaining standardized component parameters, reducing complexity and cost.
3Reliability
If floating capacitor cells are used to reduce switch stress, then reliability is improved, but spurious inductances and voltage constraints increase
Solution Approach 1:
The invention applies different cell configurations to different positions in the cascade: NPC-type cells are used in the first stage where they benefit from direct connection to the voltage source, while capacitive cells are used in the second stage where they provide floating voltage references. Each cell type is optimally positioned to minimize its negative effects and maximize its benefits.
Solution Approach 2:
The capacitive cells are configured with identical energy storage devices having the same voltage withstand capability, creating equipotential relationships between corresponding nodes in the cascade. This symmetry helps balance the voltage distribution and minimize spurious inductances by ensuring uniform electrical characteristics across all capacitive cells.
4Stress or pressure
If non-standard capacitor voltage ratings are used to achieve higher voltage levels, then voltage level is improved, but cost and manufacturing complexity increase
Solution Approach 1:
The invention maintains standardized capacitor parameters by using identical energy storage devices with the same voltage withstand capability (Uc) throughout the system. The high voltage capability is achieved not by using higher-voltage-rated capacitors, but by cascading multiple standardized capacitors in series within each capacitive cell and using the multiplication effect of the multi-stage configuration to achieve overall voltage levels above 13.8 kV.
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
Enables operation at higher voltage levels up to 13.8 kV, reduces costs and improves reliability, limits spurious inductances, and maintains standard capacitor voltage withstand, enhancing the overall efficiency and performance of the converter.
Implementation Method 1
a capacitive cell comprises two energy storage devices arranged in series, these energy storage devices having one and the same energy storage capacity
Data Source
AI summary
This is a multi-level converter comprising one or more arms (B) to each be connected between a voltage source (VDC) and a current source (I). Each arm comprises two stages (E1, E2) in cascade, the first to be connected to the voltage source (VDC), the second to be connected to the current source (I). The first stage (Et1) comprises several elementary stages (E1n, . . . , E12, E11) of rank one to n in cascade, the elementary stage (E11) of rank one being connected to the second stage (Et2) and the elementary stage (E1n) of rank n having to be connected to the voltage source (VDC). Each elementary stage (E1n) comprises a pair of identical cells of NPC type (Cen1, Cen2) in series, the connection being direct in the elementary stage of rank 1, the connection being made via n−1 capacitive cells ((Can(1), . . . , Can(n−1)) for each elementary stage of rank greater than one, the second stage (Et2) comprising a floating capacitor cell (Ce10).