Cascaded H-Bridge DC Supply for Transformer-Lite Subway Stations
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Solution Overview
Problem
The existing alternating current power supply system for subway stations is inefficient due to the need for numerous bulky and heavy power frequency transformers, resulting in high no-load loss and reactive power consumption, which increases investment costs and environmental emissions.
Innovation Solution
A direct current power supply system using a cascaded H-bridge medium-voltage converter with a common DC bus and power factor correction technology replaces traditional transformers, eliminating the need for SVG devices and reducing no-load loss and material usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power frequency transformers are used to step down voltage in the alternating current power supply system, then the power supply can be distributed to subway stations, but the transformers become bulky and heavy, increasing installation and maintenance difficulty
Solution Approach 1:
The patent changes the operating parameters from traditional power frequency (50/60Hz) to medium voltage frequency (kHz range), enabling the use of lightweight medium voltage transformers instead of bulky power frequency transformers. This parameter change fundamentally alters the transformer characteristics, achieving both power supply capability and weight reduction.
Solution Approach 2:
The patent replaces the mechanical power frequency transformation system with an electronic medium voltage transformation system using IGBT-based converters. This substitution eliminates the need for large iron and copper components, significantly reducing transformer weight while maintaining power supply function.
2Power
If power frequency transformers are used in the power supply system, then voltage can be stepped down for distribution, but the no-load loss increases significantly, consuming energy even when not in use
Solution Approach 1:
By changing from power frequency to medium voltage frequency operation, the patent enables transformers to operate at higher frequencies where core losses are significantly reduced. The medium voltage transformers can be switched off or operated at minimal load when not needed, eliminating continuous no-load energy consumption.
Solution Approach 2:
The patent implements periodic switching of medium voltage transformers based on actual power demand. Unlike power frequency transformers that must remain continuously energized, medium voltage transformers can be switched on and off periodically, eliminating no-load losses during periods of low or zero demand.
3Power
If power frequency transformers are deployed in subway stations, then power distribution is achieved, but reactive power consumption increases, requiring additional SVG compensation devices and increasing investment cost
Solution Approach 1:
The patent replaces the passive power frequency transformation system with an active medium voltage conversion system using IGBT converters. These electronic converters provide inherent power factor correction capabilities, eliminating the need for separate SVG compensation devices and reducing reactive power consumption.
Solution Approach 2:
The medium voltage converter performs multiple functions simultaneously: voltage transformation, power factor correction, and reactive power compensation. This multi-functionality eliminates the need for separate SVG devices, reducing both reactive power consumption and investment costs.
4Power
If a large number of power frequency transformers are installed in subway stations, then power supply coverage is improved, but the system complexity and investment cost increase due to the need for SVG devices and extensive transformer infrastructure
Solution Approach 1:
The patent merges the functions of power frequency transformers and SVG compensation devices into a single medium voltage converter system. This integration eliminates the need for separate SVG devices and reduces the overall number of components, simplifying the power supply system while maintaining full functionality.
Solution Approach 2:
By changing to medium voltage frequency operation, the patent enables a more compact and integrated system architecture. The medium voltage converters can be directly connected to the traction system, eliminating the need for extensive power frequency transformer infrastructure and reducing system complexity.
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 solution significantly reduces energy consumption, emissions, and investment costs by minimizing transformer-related losses and eliminating the need for SVG devices, achieving substantial power savings and cost reductions.
Implementation Method 1
the cascaded modular medium-voltage converter can use a power factor correction (PFC) technology to compensate the reactive power in the station
Data Source
AI summary
The present invention discloses a direct current power supply system for urban rail transit cascaded direct-hanging stations, belonging to the field of power electronic technologies. The power supply system includes a 110 kV high-voltage power grid, a 35 kV medium-voltage power grid, a cascaded H-bridge medium-voltage direct-hanging converter, a 650V-800V common direct current bus, a standby power supply and direct current electric loads. The cascaded H-bridge medium-voltage direct-hanging converter is formed by 3n modules in cascade, and each module is formed by an H-bridge converter and an isolated DC/DC converter connected in series. The present invention can replace an alternating current load power supply system based on a power frequency transformer, improve the efficiency and power density of the load power supply system of a subway station, reduce the no-load loss and extra cost introduced by the power frequency transformer, and achieve the purposes of energy saving, emission reduction and cost saving.