Variable Voltage Source for DC Rail Power Storage
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Solution Overview
Problem
Conventional power storage devices for DC electric railroads face challenges in safely and controllably managing load and voltage variations in overhead lines, leading to increased facility size and safety concerns due to the need for multiple converters and enhanced insulation.
Innovation Solution
A power storage device comprising a power storage element, a variable voltage source, an interconnection reactor, and a control circuit that adjusts voltage differences to manage load and voltage variations, reducing the size of the facility and enhancing safety by using a small-size variable voltage source and controlling current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a step-up/down chopper circuit is used for voltage conversion between storage battery and overhead line, then the converter can interconnect with the feeding line, but unlimited current flows to the overhead line when overhead line voltage lowers, requiring high current rating and increasing converter size
Solution Approach 1:
The patent introduces a series converter as an intermediary device between the storage battery converter and the overhead line. This series converter bears the voltage difference and controls current flow, preventing unlimited current from flowing to the overhead line when voltage drops, thereby allowing the main converter to operate at lower current ratings and reducing its size
Solution Approach 2:
The patent divides the voltage conversion function into two separate converters working in series: a main converter for power conversion and a series converter for voltage adjustment and current control. This segmentation allows each converter to be optimized for its specific function, with the series converter handling voltage variations and the main converter focusing on power conversion at reduced current ratings
2Reliability
If storage battery voltage is set lower than minimum overhead line voltage to prevent unlimited current, then current control is improved, but converter requires high current rating increasing facility size
Solution Approach 1:
The series converter acts as an intermediary that allows the storage battery voltage to be set higher than the minimum overhead line voltage while still preventing unlimited current flow. The series converter controls the voltage difference and current flow, enabling both reliable current control and reduced converter capacity
3Stability of the object's composition
If multiple converters are installed to manage load and voltage variations, then power supply stability is improved, but facility complexity and size increase
Solution Approach 1:
The patent segments the power conversion system into two specialized converters with distinct functions: the main converter for bidirectional power flow and the series converter for voltage control and current regulation. This functional segmentation achieves power supply stability while maintaining clear system architecture and control logic
Solution Approach 2:
The series converter performs multiple functions simultaneously: it controls voltage differences, regulates current flow, and enables bidirectional power flow. This multi-functionality reduces the need for additional specialized devices, managing complexity while achieving stable power supply
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
The solution enables stable power supply and reduced facility size while improving controllability and safety, effectively managing load and voltage variations in DC electric railroads.
Implementation Method 1
generating a second DC voltage equal to a difference between output voltages of the DC electric line and the power storage element
Implementation Method 2
insertion of a converter in series with a converter... each of the converters can be reduced in size because the converter for series compensation bears the load
Data Source
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AI summary
A power storage device in an embodiment includes a power storage element, a variable voltage source, an interconnection reactor, a current detector, and a control circuit. The power storage element is connected to a DC electric line having a first electrode and a second electrode and capable of being charged from and discharging to the DC electric line. The variable voltage source is connected in series between the first electrode of the DC electric line and a positive electrode of the power storage element and capable of generating a DC voltage in a range of differences between output voltages of the DC electric line and the power storage element. The interconnection reactor is connected between the first electrode of the DC electric line and the variable voltage source. The current detector detects a current flowing through the interconnection reactor. The control circuit controls the variable voltage source using the current detected by the current detector to adjust a difference between output voltages of a whole circuit and the charging element.