Rail Vehicle Rectifier System Voltage Stability
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Solution Overview
Problem
Power converter systems for rail vehicles face challenges in maintaining a constant auxiliary voltage supply due to significant fluctuations in overhead line DC voltage, particularly when the DC voltage drops, making it difficult to provide the required 650 VAC for delta-star transformers, and existing solutions like additional DC/DC converters are costly and reduce efficiency.
Innovation Solution
A power converter system that includes at least two DC voltage lines, line power converters, a polyphase delta-star transformer, auxiliary converters, and a switching unit that can operate in both AC and DC modes, allowing for the connection of unused mains converters to generate phase voltages independently, thereby compensating for DC voltage fluctuations and ensuring a stable auxiliary voltage supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a DC/DC converter is provided between the overhead line and the DC power lines to maintain stable auxiliary voltage, then the auxiliary voltage stability is improved, but the system cost increases and efficiency decreases
Solution Approach 1:
The patent applies multi-functionality by enabling the auxiliary converters to operate in two different modes: 2.5-phase operation during normal AC supply conditions and three-phase operation during DC supply conditions or voltage fluctuations. This allows the same hardware to serve multiple functions without requiring additional DC/DC converters, thereby maintaining auxiliary voltage stability while avoiding the efficiency losses and costs associated with extra conversion stages
2Stability of the object's composition
If the auxiliary converter is designed for constant low output voltage with varying input voltage over the whole possible range, then the auxiliary voltage stability is improved, but the number of semiconductor components increases and device complexity increases
Solution Approach 1:
The patent implements dynamics by allowing the auxiliary converter configuration to change dynamically between 2.5-phase and three-phase operation modes based on the input voltage conditions. The converter adapts its topology and control strategy according to whether the input is AC or DC, and whether the DC voltage is within acceptable ranges, thereby maintaining stability without requiring oversized components designed for the worst-case scenario
3Device complexity
If two-phase operation of the auxiliary converter is used to save on auxiliary converter components, then the device complexity is reduced, but the maximum modulation index is limited to 0.577 which cannot achieve the required output voltage when intermediate circuit voltage drops to 1000 VDC
Solution Approach 1:
The patent resolves this contradiction by making the auxiliary converter dynamic - it operates in 2.5-phase mode during normal conditions to reduce complexity, but can switch to three-phase operation when higher output voltage is required and the intermediate circuit voltage drops, thereby achieving both simplicity and sufficient power capability as needed
4Power
If an auxiliary transformer with tap changers is used to provide constant power regardless of mains voltage, then the power stability is improved, but the device weight increases and manufacturing cost increases
Solution Approach 1:
The patent replaces the mechanical tap changer system with an electronic control approach. Instead of physically changing transformer turns ratios through mechanical switches, the system uses power electronic converters to synthesize the required output voltage through pulse width modulation and configurable operating modes, thereby achieving power stability without the weight and complexity of tap changers
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 system provides a stable auxiliary voltage supply across varying DC input voltages, reducing the need for expensive tap changers and high-power semiconductor components, while maintaining efficiency and reliability by utilizing existing converters for multi-phase control.
Implementation Method 1
a plurality of line power converters for converting an input AC voltage to a DC supply voltage on the DC voltage lines
Implementation Method 2
a polyphase delta-star transformer to generate an auxiliary supply voltage; several auxiliary power converters for providing phase voltages for the supply transformer
Data Source
Figure 1
Figure 2
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AI summary
The invention relates to a rectifier system (1) for a vehicle, in particular a railway vehicle that can be operated in a plurality of power supply systems, comprising: at least two DC voltage conductors (5, 6, 7) for providing DC voltage potentials, a plurality of grid rectifiers (8) for converting an input-side AC voltage into a DC voltage supply on the DC voltage conductors; a supply transformer (21), in particular a multiphase delta-star transformer, for generating an auxiliary supply voltage; a plurality of auxiliary rectifiers (20) for providing phase voltages for the supply transformer, a switching unit (11, 13) designed to apply an applied AC voltage to the grid rectifier (8) in a first operating mode and to apply an applied DC supply voltage to the DC voltage conductors (5, 6, 7) in a second operation mode; and a selector switch (22) for connecting at least one of the grid rectifiers (8) to the supply transformer (21) in the second operating mode, in order to apply to the supply transformer (21) a phase voltage generated in the at least one grid rectifier (8) from the DC supply voltage. The invention further relates to operating such a rectifier system (1).