Cascade Power Cells with High-Frequency Transformers
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Solution Overview
Problem
Existing power transmission systems for medium-voltage environments face challenges with high costs and large transformer sizes due to the need for serial connections of power semiconductor switches and expensive high-voltage components, as well as increased stress on motor windings from high-amplitude voltage pulses.
Innovation Solution
A method using low-voltage single-phase power cells connected in a cascade configuration with high-frequency transformers to achieve a multistep voltage pattern, reducing component requirements and costs, and enabling efficient galvanic isolation while maintaining a compact transformer design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If power semiconductor switches are connected in series to achieve medium-voltage operation, then voltage endurance is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent divides the medium-voltage power conversion system into multiple low-voltage power cells (e.g., four 1700V IGBT modules per phase) connected in series. Each power cell operates at a lower voltage level, allowing the use of commercially available, cost-effective low-voltage components while achieving the required medium-voltage output through series connection. This segmentation resolves the contradiction by enabling voltage endurance without requiring complex custom high-voltage components.
Solution Approach 2:
The patent introduces a neutral point clamp (NPC) circuit configuration as an intermediary structure that enables series connection of low-voltage power cells. The neutral point clamping diodes and capacitors create intermediate voltage levels, allowing the series-connected IGBT modules to share voltage stress and operate within their rated voltage limits. This intermediary structure achieves medium-voltage operation while maintaining compatibility with standard low-voltage power semiconductor components.
2Strength
If NPC circuit with high-voltage power components is used, then voltage endurance is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive, custom-manufactured high-voltage power semiconductor components with multiple cheaper, commercially available low-voltage IGBT modules. By using standard 1700V IGBTs in series configuration rather than single 6500V or higher voltage modules, the system achieves equivalent voltage endurance while significantly reducing component cost and improving availability of replacement parts.
3Ease of manufacture
If low-voltage frequency converter with transformers is used, then cost is reduced, but voltage pulses increase stress on motor windings
Solution Approach 1:
The patent changes the voltage waveform parameters by generating a multistep voltage pattern with multiple discrete voltage levels (e.g., ±1700V, ±3400V, ±5100V) instead of simple bipolar switching. This multistep pattern reduces the rate of change of voltage (dv/dt) and minimizes voltage reflections on long motor cables, thereby reducing stress on motor windings while maintaining cost-effectiveness through the use of standard low-voltage IGBT modules.
4Ease of manufacture
If cascade circuit with low-voltage power cells is used, then component cost is reduced, but transformer size and cost increase
Solution Approach 1:
The patent extracts the voltage transformation function from traditional large, 50/60Hz power transformers and replaces it with high-frequency (e.g., 20kHz) transformers integrated into each power cell. By operating at high frequency, the transformers can be made much smaller while providing the same voltage transformation ratio. This extraction and reimplementation of the transformation function at high frequency reduces overall transformer size and cost while maintaining the cascade circuit's cost advantages.
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 approach reduces the number and size of components needed for voltage filtering, lowers costs, and minimizes stress on motor windings by using low-voltage power cells and high-frequency transformers, resulting in a more economical and reliable power transmission system.
Implementation Method 1
high-frequency transformers to achieve a multistep voltage pattern, reducing component requirements and costs, and enabling efficient galvanic isolation
Data Source
AI summary
Method and apparatus for controlling an apparatus transmitting power between two electricity networks or between an electricity network and a polyphase electric machine (M/G), which electricity networks can be polyphase alternating-current networks or one of them can be a single-phase direct-current network, and which apparatus comprises low-voltage power cells (C), which comprise a single-phase output connection (OUT). The power cells also comprise a single-phase input connector (IN), the power cells are arranged into groups (G1 - GN, GP1 - GPN1, GS1 - GSN2, G1"'- GN"') such that at least one power cell per each phase of the electricity network or of the electric machine belongs to each group, and the input terminals (IN) of all the power cells belonging to the same group are connected to a common transformer, which transformer comprises its own separate winding that is galvanically isolated from the others for the power cell connected to it. The controllable power semiconductor switches connected to the input connectors (IN) of all the power cells supplying power to the same transformer are controlled essentially cophasally with a 50% pulse ratio.