Delta-Connected Multilevel Inverter Using Coupled Transformers
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Solution Overview
Problem
Delta-connected cascaded H-bridge multilevel inverters require a greater number of H-bridges than star-connected configurations to achieve the same line-to-line grid voltage, leading to increased size and cost, as well as higher switching and conduction losses, which negatively impact efficiency.
Innovation Solution
The introduction of a delta-connected cascaded multilevel inverter topology that uses three coupled transformers instead of inductors to synthesize line-line voltage levels, allowing for the same number of voltage levels as star-connected configurations with the same number of switches, thereby reducing the number of required H-bridges and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If delta-connected cascaded H-bridge topology is used, then individual phase control and STATCOM application capability are improved, but the number of H-bridges required increases to 3 times compared to star connection
Solution Approach 1:
The patent introduces a current transformer as an intermediary component in the delta-connected topology. The current transformer couples the H-bridge output to the grid, enabling individual phase control and STATCOM functionality while reducing the number of H-bridges required. The transformer acts as a mediator that allows the system to achieve the desired control capabilities with fewer power semiconductor devices.
2Reliability
If delta connection is used to achieve line-to-line grid voltage, then the topology is suitable for STATCOM applications, but the number of bridges must be 3 times larger than star connection
Solution Approach 1:
The current transformer serves as an intermediary that enables the delta-connected topology to achieve STATCOM application suitability with fewer bridges. By introducing the transformer, the system can handle negative sequence reactive power and provide individual phase control without requiring 3 times as many H-bridges as conventional delta connections.
3Stress or pressure
If more H-bridges are cascaded in series to achieve line-to-line grid voltage in delta connection, then the voltage level is sufficient, but the size of the converter increases
Solution Approach 1:
The current transformer acts as an intermediary that enables voltage transformation, allowing the converter to achieve sufficient line-to-line grid voltage with fewer H-bridges. This reduces the overall converter size while maintaining the required voltage output level for grid connection.
4Power
If delta-connected topology with more H-bridges is used, then the voltage synthesis is achieved, but switching and conduction losses increase, negatively impacting efficiency
Solution Approach 1:
The current transformer serves as an intermediary that enables voltage synthesis with fewer H-bridges. By reducing the number of power semiconductor devices required, the transformer indirectly reduces both switching losses (fewer devices to switch) and conduction losses (fewer devices in the current path), thereby improving overall system efficiency while maintaining the required power output.
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 configuration maintains the same line-line voltage levels as star-connected topologies while using fewer semiconductor devices, reducing costs and improving efficiency by minimizing switching and conduction losses, and allows for sinusoidal power waveform generation in high voltage, high power AC systems.
Implementation Method 1
The introduction of a delta-connected cascaded multilevel inverter topology that uses three coupled transformers instead of inductors to synthesize line-line voltage levels
Data Source
AI summary
The cascaded multilevel inverter utilizes a delta polyphase circuit and transformers in each leg using cross-phase connection windings. Transformers corresponding to a number of phases of the inverter use an in-phase connection winding and a cross-phase connection winding to respective other legs, so that the respective transformers having the in-phase connection windings are connected in series with a DC power supply.